| 0/0 |
2026/05/31 00:55 |
flow |
assessment-security |
1h09m
Results: map[DenialOfService:false Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the vulnerability:
**Root Cause Analysis:**
The warning `WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))` in
`__getblk_slow()` is triggered when a filesystem attempts to read a block using
a size that is not aligned to the underlying block device's logical block size.
In the provided syzkaller reproducer, this is caused by a data race involving
the Network Block Device (NBD). The reproducer concurrently executes an NBD
ioctl (`NBD_DO_IT`) and a `mount` system call for the UDF filesystem on the same
NBD device.
1. Initially, the NBD device has a default logical block size of 512 bytes.
2. The `mount` system call starts and `udf_fill_super()` initializes its block
size to the device's current logical block size (512 bytes).
3. Concurrently, the `NBD_DO_IT` ioctl executes `nbd_start_device()`, which
synchronously updates the device's logical block size to 1024 bytes (the default
NBD block size).
4. When the UDF filesystem proceeds to read the Volume Recognition Sequence
(VRS) via `sb_bread()`, it requests a 512-byte block.
5. `__getblk_slow()` checks if the requested size (512) is aligned to the *new*
logical block size (1024). Since it is not, the warning is triggered.
**Security Impact:**
- **Exploitable:** No. The `WARN_ON_ONCE` simply prints a warning to the kernel
log and returns `NULL`. The UDF filesystem code (`udf_read_tagged`,
`udf_check_anchor_block`, etc.) properly handles the `NULL` return value from
the buffer cache and fails gracefully. There is no memory corruption,
out-of-bounds access, or use-after-free.
- **Denial of Service:** No. In production builds (where `panic_on_warn` is
disabled), the kernel will not crash or hang. The mount operation will simply
fail.
- **Unprivileged / User Namespace Access:** No. The NBD ioctls (`NBD_DO_IT`,
`NBD_SET_BLKSIZE`, etc.) strictly require `CAP_SYS_ADMIN` in the initial user
namespace (`capable(CAP_SYS_ADMIN)`). Unprivileged users or users within a user
namespace cannot configure NBD devices to trigger this race. Other software
block devices like `loop` safely prevent block size changes while the device is
exclusively claimed (mounted) via `bd_prepare_to_claim()`.
- **Peripheral Trigger:** Yes. A malicious USB mass storage device could
theoretically trigger this by simulating a media change and altering its
reported sector size in its `READ CAPACITY` response while the kernel is
concurrently probing/mounting it (via `sd_revalidate_disk` updating the queue
limits). However, the impact remains limited to a harmless warning.
- **VM Host/Guest Trigger:** No. Virtio block devices (`virtio-blk`) read their
block size during the initial probe and do not support the host dynamically
changing the logical block size afterward (`virtblk_update_capacity` only
updates the total capacity, not the block size).
**Conclusion:**
This is a harmless race condition resulting in a kernel warning. It requires
root privileges to trigger via NBD and does not pose a security risk (no memory
corruption, privilege escalation, or denial of service). Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/31 00:55 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
static long syz_open_dev(volatile long a0, volatile long a1, volatile long a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
unsigned long nb = a1;
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(nb % 10);
nb /= 10;
}
return open(buf, a2 & ~O_CREAT, 0);
}
}
uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// openat$dir arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 31 00} (length 0x8)
// }
// flags: open_flags = 0x40042 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd_dir
memcpy((void*)0x200000001a00, "./file1\000", 8);
syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000001a00ul, /*flags=O_NOATIME|O_CREAT|O_RDWR*/0x40042, /*mode=*/0);
// syz_open_dev$ndb arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6e 62 64 23 00} (length 0xa)
// }
// id: proc = 0x0 (8 bytes)
// flags: open_flags = 0x80000 (8 bytes)
// ]
// returns fd_nbd
memcpy((void*)0x2000000000c0, "/dev/nbd#\000", 10);
res = -1;
res = syz_open_dev(/*dev=*/0x2000000000c0, /*id=*/0, /*flags=O_CLOEXEC*/0x80000);
if (res != -1)
r[0] = res;
// socket arguments: [
// domain: socket_domain = 0x2 (8 bytes)
// type: socket_type = 0x1 (8 bytes)
// proto: int32 = 0x0 (4 bytes)
// ]
// returns sock
res = syscall(__NR_socket, /*domain=AF_INET*/2ul, /*type=SOCK_STREAM*/1ul, /*proto=*/0);
if (res != -1)
r[1] = res;
// syz_open_dev$ndb arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6e 62 64 23 00} (length 0xa)
// }
// id: proc = 0x0 (8 bytes)
// flags: open_flags = 0x0 (8 bytes)
// ]
// returns fd_nbd
memcpy((void*)0x200000000000, "/dev/nbd#\000", 10);
res = -1;
res = syz_open_dev(/*dev=*/0x200000000000, /*id=*/0, /*flags=*/0);
if (res != -1)
r[2] = res;
// ioctl$NBD_SET_SOCK arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab00 (4 bytes)
// arg: sock_nbd_client (resource)
// ]
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xab00, /*arg=*/r[1]);
// ioctl$NBD_DO_IT arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab03 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0);
// mount arguments: [
// src: ptr[in, blockdev_filename] {
// union blockdev_filename {
// nbd: nbd_filename {
// prefix: buffer: {2f 64 65 76 2f 6e 62 64} (length 0x8)
// id: proc = 0x0 (1 bytes)
// z: const = 0x0 (1 bytes)
// }
// }
// }
// dst: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 31 00} (length 0x8)
// }
// type: ptr[in, buffer] {
// buffer: {75 64 66 00} (length 0x4)
// }
// flags: mount_flags = 0x2008087 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000000000, "/dev/nbd", 8);
*(uint8_t*)0x200000000008 = 0x30;
*(uint8_t*)0x200000000009 = 0;
memcpy((void*)0x200000004a00, "./file1\000", 8);
memcpy((void*)0x200000000080, "udf\000", 4);
syscall(__NR_mount, /*src=*/0x200000000000ul, /*dst=*/0x200000004a00ul, /*type=*/0x200000000080ul, /*flags=MS_LAZYTIME|MS_SILENT|MS_RDONLY|MS_NOSUID|MS_NODEV|0x80*/0x2008087ul, /*data=*/0ul);
return 0;
}
]
|
| 2/1 |
2026/05/31 00:55 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/d5c734f95e45056235abda1a957b354a26ab9ce7]
|
| 3/1 |
2026/05/31 00:57 |
action |
kernel-builder |
28m
Results: map[KernelObj:/app/workdir/cache/build/05f71715270433d91e10c23901ae8cfc5913daf5]
|
| 4/1 |
2026/05/31 01:26 |
action |
codesearch-prepare |
25m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/31 01:51 |
agent |
expert |
12m
Model:
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Instruction: You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by grepping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completely wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control transfers, that also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidential Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 __getblk_slow fs/buffer.c:1125 [inline]
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 bdev_getblk+0x580/0x660 fs/buffer.c:1461
Modules linked in:
CPU: 0 UID: 0 PID: 5719 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:__getblk_slow fs/buffer.c:1125 [inline]
RIP: 0010:bdev_getblk+0x580/0x660 fs/buffer.c:1461
Code: 26 fb ff ff e8 61 2d 78 ff 48 c7 c7 60 05 9a 8b 48 c7 c6 55 e0 a0 8d 4c 89 fa 4c 89 e9 e8 58 0f e0 fe eb bd e8 41 2d 78 ff 90 <0f> 0b 90 48 b8 00 00 00 00 00 fc ff df 41 80 3c 07 00 74 08 48 89
RSP: 0018:ffffc9000d18f6b0 EFLAGS: 00010293
RAX: ffffffff824790bf RBX: ffff888032185098 RCX: ffff888033aaa440
RDX: 0000000000000000 RSI: 0000000000000200 RDI: 0000000000000000
RBP: 0000000000000200 R08: 0000000000000000 R09: ffffffff8217593d
R10: 0000000000000406 R11: 0000000000000000 R12: ffff8880321859f0
R13: ffff888032185080 R14: 0000000000000200 R15: 1ffff11006430a13
FS: 00007f265a53c6c0(0000) GS:ffff88808d20c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000559033e08008 CR3: 00000000515c2000 CR4: 0000000000352ef0
Call Trace:
<TASK>
__bread_gfp+0x89/0x3c0 fs/buffer.c:1515
sb_bread include/linux/buffer_head.h:346 [inline]
udf_read_tagged+0xad/0xe00 fs/udf/misc.c:199
udf_check_anchor_block+0x99/0x550 fs/udf/super.c:1912
udf_scan_anchors fs/udf/super.c:1952 [inline]
udf_load_vrs+0x6e3/0xf20 fs/udf/super.c:2033
udf_fill_super+0x5ad/0x17a0 fs/udf/super.c:2201
get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1692
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
do_mount fs/namespace.c:4136 [inline]
__do_sys_mount fs/namespace.c:4347 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4324
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f265978ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f265a53c038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f26599c6090 RCX: 00007f265978ebe9
RDX: 0000200000000080 RSI: 0000200000004a00 RDI: 0000200000000000
RBP: 00007f2659811e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000002008087 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f26599c6128 R14: 00007f26599c6090 R15: 00007ffe80675be8
</TASK>
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
static long syz_open_dev(volatile long a0, volatile long a1, volatile long a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
unsigned long nb = a1;
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(nb % 10);
nb /= 10;
}
return open(buf, a2 & ~O_CREAT, 0);
}
}
uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// openat$dir arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 31 00} (length 0x8)
// }
// flags: open_flags = 0x40042 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd_dir
memcpy((void*)0x200000001a00, "./file1\000", 8);
syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000001a00ul, /*flags=O_NOATIME|O_CREAT|O_RDWR*/0x40042, /*mode=*/0);
// syz_open_dev$ndb arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6e 62 64 23 00} (length 0xa)
// }
// id: proc = 0x0 (8 bytes)
// flags: open_flags = 0x80000 (8 bytes)
// ]
// returns fd_nbd
memcpy((void*)0x2000000000c0, "/dev/nbd#\000", 10);
res = -1;
res = syz_open_dev(/*dev=*/0x2000000000c0, /*id=*/0, /*flags=O_CLOEXEC*/0x80000);
if (res != -1)
r[0] = res;
// socket arguments: [
// domain: socket_domain = 0x2 (8 bytes)
// type: socket_type = 0x1 (8 bytes)
// proto: int32 = 0x0 (4 bytes)
// ]
// returns sock
res = syscall(__NR_socket, /*domain=AF_INET*/2ul, /*type=SOCK_STREAM*/1ul, /*proto=*/0);
if (res != -1)
r[1] = res;
// syz_open_dev$ndb arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6e 62 64 23 00} (length 0xa)
// }
// id: proc = 0x0 (8 bytes)
// flags: open_flags = 0x0 (8 bytes)
// ]
// returns fd_nbd
memcpy((void*)0x200000000000, "/dev/nbd#\000", 10);
res = -1;
res = syz_open_dev(/*dev=*/0x200000000000, /*id=*/0, /*flags=*/0);
if (res != -1)
r[2] = res;
// ioctl$NBD_SET_SOCK arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab00 (4 bytes)
// arg: sock_nbd_client (resource)
// ]
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xab00, /*arg=*/r[1]);
// ioctl$NBD_DO_IT arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab03 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0);
// mount arguments: [
// src: ptr[in, blockdev_filename] {
// union blockdev_filename {
// nbd: nbd_filename {
// prefix: buffer: {2f 64 65 76 2f 6e 62 64} (length 0x8)
// id: proc = 0x0 (1 bytes)
// z: const = 0x0 (1 bytes)
// }
// }
// }
// dst: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 31 00} (length 0x8)
// }
// type: ptr[in, buffer] {
// buffer: {75 64 66 00} (length 0x4)
// }
// flags: mount_flags = 0x2008087 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000000000, "/dev/nbd", 8);
*(uint8_t*)0x200000000008 = 0x30;
*(uint8_t*)0x200000000009 = 0;
memcpy((void*)0x200000004a00, "./file1\000", 8);
memcpy((void*)0x200000000080, "udf\000", 4);
syscall(__NR_mount, /*src=*/0x200000000000ul, /*dst=*/0x200000004a00ul, /*type=*/0x200000000080ul, /*flags=MS_LAZYTIME|MS_SILENT|MS_RDONLY|MS_NOSUID|MS_NODEV|0x80*/0x2008087ul, /*data=*/0ul);
return 0;
}
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the vulnerability:
**Root Cause Analysis:**
The warning `WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))` in `__getblk_slow()` is triggered when a filesystem attempts to read a block using a size that is not aligned to the underlying block device's logical block size.
In the provided syzkaller reproducer, this is caused by a data race involving the Network Block Device (NBD). The reproducer concurrently executes an NBD ioctl (`NBD_DO_IT`) and a `mount` system call for the UDF filesystem on the same NBD device.
1. Initially, the NBD device has a default logical block size of 512 bytes.
2. The `mount` system call starts and `udf_fill_super()` initializes its block size to the device's current logical block size (512 bytes).
3. Concurrently, the `NBD_DO_IT` ioctl executes `nbd_start_device()`, which synchronously updates the device's logical block size to 1024 bytes (the default NBD block size).
4. When the UDF filesystem proceeds to read the Volume Recognition Sequence (VRS) via `sb_bread()`, it requests a 512-byte block.
5. `__getblk_slow()` checks if the requested size (512) is aligned to the *new* logical block size (1024). Since it is not, the warning is triggered.
**Security Impact:**
- **Exploitable:** No. The `WARN_ON_ONCE` simply prints a warning to the kernel log and returns `NULL`. The UDF filesystem code (`udf_read_tagged`, `udf_check_anchor_block`, etc.) properly handles the `NULL` return value from the buffer cache and fails gracefully. There is no memory corruption, out-of-bounds access, or use-after-free.
- **Denial of Service:** No. In production builds (where `panic_on_warn` is disabled), the kernel will not crash or hang. The mount operation will simply fail.
- **Unprivileged / User Namespace Access:** No. The NBD ioctls (`NBD_DO_IT`, `NBD_SET_BLKSIZE`, etc.) strictly require `CAP_SYS_ADMIN` in the initial user namespace (`capable(CAP_SYS_ADMIN)`). Unprivileged users or users within a user namespace cannot configure NBD devices to trigger this race. Other software block devices like `loop` safely prevent block size changes while the device is exclusively claimed (mounted) via `bd_prepare_to_claim()`.
- **Peripheral Trigger:** Yes. A malicious USB mass storage device could theoretically trigger this by simulating a media change and altering its reported sector size in its `READ CAPACITY` response while the kernel is concurrently probing/mounting it (via `sd_revalidate_disk` updating the queue limits). However, the impact remains limited to a harmless warning.
- **VM Host/Guest Trigger:** No. Virtio block devices (`virtio-blk`) read their block size during the initial probe and do not support the host dynamically changing the logical block size afterward (`virtblk_update_capacity` only updates the total capacity, not the block size).
**Conclusion:**
This is a harmless race condition resulting in a kernel warning. It requires root privileges to trigger via NBD and does not pose a security risk (no memory corruption, privilege escalation, or denial of service).
|
| 6/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 9648
output: 34
thoughts: 253
Thoughts: **Investigating a Potential Block Allocation Issue**
Okay, here's what I'm seeing: there's a WARNING flagged in `__getblk_slow` located in `fs/buffer.c` at line 1125. The specific call originates from `bdev_getblk`. My initial instinct is to dig into the call trace to understand the context and why this is being triggered.
The trace looks like this: `__bread_gfp` then `sb_bread`, which is an inline function, then `udf_read_tagged`, then `udf_check_anchor_block`, which calls an inline `udf_scan_anchors`, and ultimately leads to `udf_load_vrs` and finally `udf_fill_super`. It seems to be related to the UDF filesystem, and specifically, to reading the volume descriptor sequence.
My next move is to head directly to `fs/buffer.c:1125` to see what's actually happening in `__getblk_slow`. From there, I can start to understand the conditions that are causing this warning and determine whether it's a known issue or a potential bug in the UDF implementation. I'll need to understand the arguments passed to this function, and then reconstruct the calling context from `udf_fill_super`. This trace certainly helps to narrow down the search.
|
| 7/2 |
2026/05/31 01:51 |
tool |
read-file |
0m
Args: map[File:fs/buffer.c FirstLine:1115 LineCount:20]
Results: map[Contents:1115: /* Create a folio with the proper size buffers */
1116: return grow_dev_folio(bdev, block, pos / PAGE_SIZE, size, gfp);
1117: }
1118:
1119: static struct buffer_head *
1120: __getblk_slow(struct block_device *bdev, sector_t block,
1121: unsigned size, gfp_t gfp)
1122: {
1123: bool blocking = gfpflags_allow_blocking(gfp);
1124:
1125: if (WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))) {
1126: printk(KERN_ERR "getblk(): block size %d not aligned to logical block size %d\n",
1127: size, bdev_logical_block_size(bdev));
1128: return NULL;
1129: }
1130:
1131: for (;;) {
1132: struct buffer_head *bh;
1133:
1134: if (!grow_buffers(bdev, block, size, gfp))
]
|
| 8/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 10569
output: 36
thoughts: 107
Thoughts: **Analyzing a Disk Alignment Warning**
Okay, so I've just encountered this `WARN_ON_ONCE` message: `WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))`. My expert intuition is immediately screaming "alignment problem!" It seems that the variable `size` isn't properly aligned to the logical block size of the block device, represented by `bdev`.
Digging a bit deeper, this warning originates from `bdev_getblk`, and that function's call stack reveals it's coming from `__bread_gfp`. Now I need to figure out where that's happening, so I'm jumping right to `udf_read_tagged` in `fs/udf/misc.c:199`. I suspect a sector or block size mismatch in the UDF filesystem code is the culprit. Time to trace the data flow and see *why* this misalignment is happening during a read operation and how the block size is being determined, perhaps there's an issue in how the data is being read or interpreted from disk.
|
| 9/2 |
2026/05/31 01:51 |
tool |
read-file |
0m
Args: map[File:fs/udf/misc.c FirstLine:185 LineCount:30]
Results: map[Contents: 185: * July 1, 1997 - Andrew E. Mileski
186: * Written, tested, and released.
187: */
188: struct buffer_head *udf_read_tagged(struct super_block *sb, uint32_t block,
189: uint32_t location, uint16_t *ident)
190: {
191: struct tag *tag_p;
192: struct buffer_head *bh = NULL;
193: u8 checksum;
194:
195: /* Read the block */
196: if (block == 0xFFFFFFFF)
197: return NULL;
198:
199: bh = sb_bread(sb, block);
200: if (!bh) {
201: udf_err(sb, "read failed, block=%u, location=%u\n",
202: block, location);
203: return NULL;
204: }
205:
206: tag_p = (struct tag *)(bh->b_data);
207:
208: *ident = le16_to_cpu(tag_p->tagIdent);
209:
210: if (location != le32_to_cpu(tag_p->tagLocation)) {
211: udf_debug("location mismatch block %u, tag %u != %u\n",
212: block, le32_to_cpu(tag_p->tagLocation), location);
213: goto error_out;
214: }
]
|
| 10/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 11425
output: 37
thoughts: 98
Thoughts: **Investigating a UDF Block Size Discrepancy**
Okay, so `sb_bread(sb, block)` is throwing a warning, and I need to figure out why. This function reads a block, specifically of size `sb->s_blocksize`. The warning is indicating that `sb->s_blocksize` isn't aligned to `bdev_logical_block_size(bdev)`, which, as an expert in this field, I know can cause performance issues and data corruption if not handled correctly.
Now, the crucial piece of the puzzle here is that `sb->s_blocksize` is actually set during the mount process. So, I need to trace back how this value is being determined. Let me take a look at `udf_fill_super` in `fs/udf/super.c`, specifically around line 2201. That's likely where the block size is being initialized or calculated for UDF filesystems, and that's where I need to start my investigation. This will give me the context I need to understand why there's a possible misalignment.
|
| 11/2 |
2026/05/31 01:51 |
tool |
read-file |
0m
Args: map[File:fs/udf/super.c FirstLine:2180 LineCount:40]
Results: map[Contents:2180: rwlock_init(&sbi->s_cred_lock);
2181:
2182: if (uopt->session == 0xFFFFFFFF)
2183: sbi->s_session = udf_get_last_session(sb);
2184: else
2185: sbi->s_session = uopt->session;
2186:
2187: udf_debug("Multi-session=%d\n", sbi->s_session);
2188:
2189: /* Fill in the rest of the superblock */
2190: sb->s_op = &udf_sb_ops;
2191: sb->s_export_op = &udf_export_ops;
2192:
2193: sb->s_magic = UDF_SUPER_MAGIC;
2194: sb->s_time_gran = 1000;
2195:
2196: if (uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)) {
2197: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2198: } else {
2199: uopt->blocksize = bdev_logical_block_size(sb->s_bdev);
2200: while (uopt->blocksize <= 4096) {
2201: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2202: if (ret < 0) {
2203: if (!silent && ret != -EACCES) {
2204: pr_notice("Scanning with blocksize %u failed\n",
2205: uopt->blocksize);
2206: }
2207: brelse(sbi->s_lvid_bh);
2208: sbi->s_lvid_bh = NULL;
2209: /*
2210: * EACCES is special - we want to propagate to
2211: * upper layers that we cannot handle RW mount.
2212: */
2213: if (ret == -EACCES)
2214: break;
2215: } else
2216: break;
2217:
2218: uopt->blocksize <<= 1;
2219: }
]
|
| 12/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 12450
output: 37
thoughts: 74
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing:
**Analyzing Block Size Initialization in UDF Filesystem Code**
Alright, so I'm looking at this bit of UDF code and it's grabbing `uopt->blocksize`, and then it appears to be multiplying it by 2 within a loop. Hmm, that seems straightforward enough at first glance. But hang on... something's nagging at me.
Where is this `uopt->blocksize` actually *coming* from? I seem to recall that the block size, specifically `sb->s_blocksize`, might get initialized somewhere else in this process. Let me just quickly confirm where that's happening. And I think `udf_load_vrs` is the likely candidate. So, yeah, I should probably check that routine to see exactly how and when `sb->s_blocksize` is being set. That's the key to understanding this multiplication and how the overall block size is managed in the UDF filesystem. Let's dig into `udf_load_vrs` now.
|
| 13/2 |
2026/05/31 01:51 |
tool |
read-file |
0m
Args: map[File:fs/udf/super.c FirstLine:2020 LineCount:30]
Results: map[Contents:2020: }
2021: if (nsr == -1)
2022: udf_debug("Failed to read sector at offset %d. "
2023: "Assuming open disc. Skipping validity "
2024: "check\n", VSD_FIRST_SECTOR_OFFSET);
2025: if (!sbi->s_last_block)
2026: sbi->s_last_block = udf_get_last_block(sb);
2027: } else {
2028: udf_debug("Validity check skipped because of novrs option\n");
2029: }
2030:
2031: /* Look for anchor block and load Volume Descriptor Sequence */
2032: sbi->s_anchor = uopt->anchor;
2033: ret = udf_scan_anchors(sb, &sbi->s_last_block, fileset);
2034: if (ret < 0) {
2035: if (!silent && ret == -EAGAIN)
2036: udf_warn(sb, "No anchor found\n");
2037: return ret;
2038: }
2039: return 0;
2040: }
2041:
2042: static void udf_finalize_lvid(struct logicalVolIntegrityDesc *lvid)
2043: {
2044: struct timespec64 ts;
2045:
2046: ktime_get_real_ts64(&ts);
2047: udf_time_to_disk_stamp(&lvid->recordingDateAndTime, ts);
2048: lvid->descTag.descCRC = cpu_to_le16(
2049: crc_itu_t(0, (char *)lvid + sizeof(struct tag),
]
|
| 14/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 13302
output: 37
thoughts: 15
Thoughts: Here's my thought process, as if I were thinking it:
**Digging into Block Size Initialization**
Okay, hold on a second. I'm deep in this code, but I've hit a point where I need to take a step back and understand the lifecycle of a key variable. Specifically, I'm trying to trace the initialization of `sb->s_blocksize`. I understand its function in the broader file system context, but I need to know *exactly* where that specific member of the superblock structure is assigned its value. It's crucial for the correct operation, so I need to understand where the size comes from to make sure the right value is being set. Now, I have to find the setting and the code!
|
| 15/2 |
2026/05/31 01:51 |
tool |
read-file |
0m
Args: map[File:fs/udf/super.c FirstLine:1980 LineCount:30]
Results: map[Contents:1980: continue;
1981: ret = udf_check_anchor_block(sb, last[i] - 256, fileset);
1982: if (ret != -EAGAIN) {
1983: if (!ret)
1984: *lastblock = last[i];
1985: return ret;
1986: }
1987: }
1988:
1989: /* Finally try block 512 in case media is open */
1990: return udf_check_anchor_block(sb, sbi->s_session + 512, fileset);
1991: }
1992:
1993: /*
1994: * Check Volume Structure Descriptor, find Anchor block and load Volume
1995: * Descriptor Sequence.
1996: *
1997: * Returns < 0 on error, 0 on success. -EAGAIN is special meaning anchor
1998: * block was not found.
1999: */
2000: static int udf_load_vrs(struct super_block *sb, struct udf_options *uopt,
2001: int silent, struct kernel_lb_addr *fileset)
2002: {
2003: struct udf_sb_info *sbi = UDF_SB(sb);
2004: int nsr = 0;
2005: int ret;
2006:
2007: if (!sb_set_blocksize(sb, uopt->blocksize)) {
2008: if (!silent)
2009: udf_warn(sb, "Bad block size\n");
]
|
| 16/2 |
2026/05/31 01:51 |
llm |
expert |
0m
Model:
Tokens:
input: 13975
output: 23
thoughts: 162
Thoughts: **Analyzing UDF Block Size Initialization**
Okay, so I'm tracing the UDF filesystem initialization and I see that `sb_set_blocksize(sb, uopt->blocksize)` gets called right at the start of `udf_load_vrs`. My initial thought is to figure out where `uopt->blocksize` is coming from. Hmm, it looks like it’s initialized with `bdev_logical_block_size(sb->s_bdev)` and then *multiplied by two*. That seems a bit odd; shouldn’t it be naturally aligned with the block device’s logical block size if it's based on it?
But hang on… I need to consider a potential user override. What happens if the `uopt->flags` field has the `UDF_FLAG_BLOCKSIZE_SET` bit set? Then the user explicitly sets the blocksize. I have to verify where this flag gets set and how the user's input impacts the final `blocksize`. Right, I need to dig into `udf_parse_options` to understand how the user-provided options are being handled.
|
| 17/2 |
2026/05/31 01:52 |
tool |
grepper |
0m
Args: map[Expression:UDF_FLAG_BLOCKSIZE_SET]
Results: map[Output:fs/udf/super.c=383=static int udf_show_options(struct seq_file *seq, struct dentry *root)
--
fs/udf/super.c-389- seq_puts(seq, ",nostrict");
fs/udf/super.c:390: if (UDF_QUERY_FLAG(sb, UDF_FLAG_BLOCKSIZE_SET))
fs/udf/super.c-391- seq_printf(seq, ",bs=%lu", sb->s_blocksize);
--
fs/udf/super.c=518=static int udf_parse_param(struct fs_context *fc, struct fs_parameter *param)
--
fs/udf/super.c-539- uopt->blocksize = n;
fs/udf/super.c:540: uopt->flags |= (1 << UDF_FLAG_BLOCKSIZE_SET);
fs/udf/super.c-541- break;
--
fs/udf/super.c=2151=static int udf_fill_super(struct super_block *sb, struct fs_context *fc)
--
fs/udf/super.c-2195-
fs/udf/super.c:2196: if (uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)) {
fs/udf/super.c-2197- ret = udf_load_vrs(sb, uopt, silent, &fileset);
--
fs/udf/udf_sb.h-32-#define UDF_FLAG_LASTBLOCK_SET 16
fs/udf/udf_sb.h:33:#define UDF_FLAG_BLOCKSIZE_SET 17
fs/udf/udf_sb.h-34-#define UDF_FLAG_INCONSISTENT 18
]
|
| 18/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 14876
output: 38
thoughts: 43
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing:
**Examining the Block Size Setting in UDF Filesystems**
Right, so `bs=` is the mount option we're focusing on, and it directly sets `uopt->blocksize`, and then sets `UDF_FLAG_BLOCKSIZE_SET`, which makes sense. I need to understand how this is handled in the overall filesystem setup. My next step is to drill down into what `sb_set_blocksize` is doing. I'm really keen on how that function interacts with the Super Block. I know this is key for defining the storage allocation and addressing in the UDF format, and I need to see how the blocksize affects this.
|
| 19/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:sb_set_blocksize]
Results: map[SourceCode: 220: int sb_set_blocksize(struct super_block *sb, int size)
221: {
222: if (!(sb->s_type->fs_flags & FS_LBS) && size > PAGE_SIZE)
223: return 0;
224: if (set_blocksize(sb->s_bdev_file, size))
225: return 0;
226: /* If we get here, we know size is validated */
227: sb->s_blocksize = size;
228: sb->s_blocksize_bits = blksize_bits(size);
229: return sb->s_blocksize;
230: }
SourceFile:block/bdev.c]
|
| 20/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 15337
output: 34
thoughts: 20
Thoughts: Here's my thought process, as if I were examining this code:
**Analyzing `set_blocksize`**
Okay, so we're looking at `set_blocksize`. The name implies it's responsible for setting the block size. My first instinct, given my experience, is to immediately check for input validation. A poorly validated block size could lead to some nasty bugs down the line - corrupted data, performance issues, or even security vulnerabilities if it's not handled correctly. So, the key here is to see how the code validates the size. I'm going to look closely at the implementation details, making sure it handles edge cases and potential errors gracefully. I'll be looking for things like size limits, data type checks, and perhaps even checking if the block size is a power of 2, if the system needs it that way. Let's see how they've handled this.
|
| 21/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:set_blocksize]
Results: map[SourceCode: 178: int set_blocksize(struct file *file, int size)
179: {
180: struct inode *inode = file->f_mapping->host;
181: struct block_device *bdev = I_BDEV(inode);
182: int ret;
183:
184: ret = bdev_validate_blocksize(bdev, size);
185: if (ret)
186: return ret;
187:
188: if (!file->private_data)
189: return -EINVAL;
190:
191: /* Don't change the size if it is same as current */
192: if (inode->i_blkbits != blksize_bits(size)) {
193: /*
194: * Flush and truncate the pagecache before we reconfigure the
195: * mapping geometry because folio sizes are variable now. If a
196: * reader has already allocated a folio whose size is smaller
197: * than the new min_order but invokes readahead after the new
198: * min_order becomes visible, readahead will think there are
199: * "zero" blocks per folio and crash. Take the inode and
200: * invalidation locks to avoid racing with
201: * read/write/fallocate.
202: */
203: inode_lock(inode);
204: filemap_invalidate_lock(inode->i_mapping);
205:
206: sync_blockdev(bdev);
207: kill_bdev(bdev);
208:
209: inode->i_blkbits = blksize_bits(size);
210: mapping_set_folio_min_order(inode->i_mapping, get_order(size));
211: kill_bdev(bdev);
212: filemap_invalidate_unlock(inode->i_mapping);
213: inode_unlock(inode);
214: }
215: return 0;
216: }
SourceFile:block/bdev.c]
|
| 22/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 16199
output: 37
thoughts: 18
Thoughts: Here's my thought process, as if I were considering this code:
**Analyzing Block Size Validation**
Okay, so I'm looking at this `set_blocksize` function, and it seems like the key function call in it is `bdev_validate_blocksize`. That's the core of the validation logic. I need to understand what that function does and, more importantly, *why* it's being called here. What are the potential vulnerabilities or issues that we are trying to mitigate by validating the block size? Are we trying to prevent a user from setting an invalid block size or are we trying to validate what an underlying device presents? Are there dependencies and how does this validate if the user, underlying device or the filesystem is responsible for the validation? Are we simply checking that blocksize isn't zero or negative?
The implications are important because a bad block size could lead to all sorts of problems—performance bottlenecks, data corruption, or even system instability. So, understanding the validation process is critical for ensuring the reliability of the storage subsystem. I need to dig deeper into the specifics of `bdev_validate_blocksize` and its interactions with the rest of the storage stack.
|
| 23/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:bdev_validate_blocksize]
Results: map[SourceCode: 155: /**
156: * bdev_validate_blocksize - check that this block size is acceptable
157: * @bdev: blockdevice to check
158: * @block_size: block size to check
159: *
160: * For block device users that do not use buffer heads or the block device
161: * page cache, make sure that this block size can be used with the device.
162: *
163: * Return: On success zero is returned, negative error code on failure.
164: */
165: int bdev_validate_blocksize(struct block_device *bdev, int block_size)
166: {
167: if (blk_validate_block_size(block_size))
168: return -EINVAL;
169:
170: /* Size cannot be smaller than the size supported by the device */
171: if (block_size < bdev_logical_block_size(bdev))
172: return -EINVAL;
173:
174: return 0;
175: }
SourceFile:block/bdev.c]
|
| 24/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 16851
output: 37
thoughts: 74
Thoughts: Okay, let me break this down.
**Block Size Validation - My Internal Audit**
Alright, so I'm looking at this `bdev_validate_blocksize` function, and my immediate concern is around block size validation. The code checks if the proposed `block_size` is *less than* the logical block size of the block device (`bdev_logical_block_size(bdev)`). That seems reasonable, a basic sanity check, right? However, hold on a second...it doesn't appear to be explicitly verifying if the `block_size` is *aligned* to the logical block size. That's a potential oversight, a critical detail often overlooked in low-level block device interactions. Misalignment can lead to performance degradation, data corruption, or even more serious issues depending on the hardware and filesystem.
Now I'm mentally scanning for the missing piece. Does the `blk_validate_block_size` function pick up the slack? It *might*, but I need to confirm that. I need to refresh my memory on the interactions of these functions and whether the necessary alignment check is being handled elsewhere in the code. I can't just assume; I need to drill down and verify.
|
| 25/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:blk_validate_block_size]
Results: map[SourceCode: 284: /* blk_validate_limits() validates bsize, so drivers don't usually need to */
285: static inline int blk_validate_block_size(unsigned long bsize)
286: {
287: if (bsize < 512 || bsize > BLK_MAX_BLOCK_SIZE || !is_power_of_2(bsize))
288: return -EINVAL;
289:
290: return 0;
291: }
SourceFile:include/linux/blkdev.h]
|
| 26/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 17388
output: 40
thoughts: 138
Thoughts: Okay, here's my take on those thoughts, framed as my own reasoning:
**Analyzing Block Size Validation**
Right, `blk_validate_block_size`... that's the one that checks if a block size is a power of 2, good. Now, if I'm understanding this correctly, the core logic hinges on a few conditions. If `block_size` *is* a power of 2, *and* it's greater than or equal to the logical block size of the block device (`bdev`), *and* that `bdev_logical_block_size(bdev)` is *also* a power of 2, then `block_size` *absolutely has to be* aligned to `bdev_logical_block_size(bdev)`. That makes sense, keeps things clean and predictable. But hang on a second... is `bdev_logical_block_size(bdev)` *always* a power of 2? I should double-check that assumption because it's pretty fundamental to the whole process. Best to verify the underlying function. Let's dig into `bdev_logical_block_size`.
|
| 27/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/blkdev.h Name:bdev_logical_block_size]
Results: map[SourceCode:1367: static inline unsigned int bdev_logical_block_size(struct block_device *bdev)
1368: {
1369: return queue_logical_block_size(bdev_get_queue(bdev));
1370: }
SourceFile:include/linux/blkdev.h]
|
| 28/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 17916
output: 39
thoughts: 13
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Initial Assessment: Logical Block Size Check**
Right, let's dive into this. The initial thought, "Let's check `queue_logical_block_size`," immediately flags a specific area of concern. It implies we're about to investigate the reported logical block size of a storage queue. This likely stems from a problem manifesting in an I/O subsystem, or perhaps a performance bottleneck analysis. There’s something requiring validation or diagnostics. Perhaps an unexpected value, or one that conflicts with an expectation based on other configuration parameters. Is it a suspected misreporting by the storage device, or a mismatch in how the host operating system interprets or exposes it? The context is key, of course, and depends on where this check is initiated, the level of abstraction, and, ideally, any correlated observations. There has to be a reason, and I'm eager to find out what it is!
|
| 29/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/blkdev.h Name:queue_logical_block_size]
Results: map[SourceCode:1362: static inline unsigned queue_logical_block_size(const struct request_queue *q)
1363: {
1364: return q->limits.logical_block_size;
1365: }
SourceFile:include/linux/blkdev.h]
|
| 30/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 18272
output: 37
thoughts: 238
Thoughts: **Alignment and Block Sizes**
Okay, let's think this through. If `block_size` is a power of 2, and it's also greater than or equal to `bdev_logical_block_size(bdev)`, which *also* happens to be a power of 2, then `block_size` *has* to be a multiple of `bdev_logical_block_size(bdev)`. That makes sense. Therefore, the `IS_ALIGNED(block_size, bdev_logical_block_size(bdev))` check *should* evaluate to true.
Now, let's recall what `IS_ALIGNED` actually *does*. It's defined as `!(x & (a - 1))`. So, if `block_size` (our `x`) is, say, 1024, and `bdev_logical_block_size` (our `a`) is 512, then we'd be looking at `1024 & (512 - 1)`, which is `1024 & 511`. And that *does* indeed equal 0, indicating alignment. Good.
But what if… what if `bdev_logical_block_size` *isn't* a power of 2? Is that even possible? I need to verify that this is always the case. Let me check the code… I need to look at `blk_validate_limits` to be sure.
|
| 31/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/blkdev.h Name:blk_validate_limits]
Results: map[SourceCode: 299: /*
300: * Check that the limits in lim are valid, initialize defaults for unset
301: * values, and cap values based on others where needed.
302: */
303: int blk_validate_limits(struct queue_limits *lim)
304: {
305: unsigned int max_hw_sectors;
306: unsigned int logical_block_sectors;
307: unsigned long seg_size;
308: int err;
309:
310: /*
311: * Unless otherwise specified, default to 512 byte logical blocks and a
312: * physical block size equal to the logical block size.
313: */
314: if (!lim->logical_block_size)
315: lim->logical_block_size = SECTOR_SIZE;
316: else if (blk_validate_block_size(lim->logical_block_size)) {
317: pr_warn("Invalid logical block size (%d)\n", lim->logical_block_size);
318: return -EINVAL;
319: }
320: if (lim->physical_block_size < lim->logical_block_size) {
321: lim->physical_block_size = lim->logical_block_size;
322: } else if (!is_power_of_2(lim->physical_block_size)) {
323: pr_warn("Invalid physical block size (%d)\n", lim->physical_block_size);
324: return -EINVAL;
325: }
326:
327: /*
328: * The minimum I/O size defaults to the physical block size unless
329: * explicitly overridden.
330: */
331: if (lim->io_min < lim->physical_block_size)
332: lim->io_min = lim->physical_block_size;
333:
334: /*
335: * The optimal I/O size may not be aligned to physical block size
336: * (because it may be limited by dma engines which have no clue about
337: * block size of the disks attached to them), so we round it down here.
338: */
339: lim->io_opt = round_down(lim->io_opt, lim->physical_block_size);
340:
341: /*
342: * max_hw_sectors has a somewhat weird default for historical reason,
343: * but driver really should set their own instead of relying on this
344: * value.
345: *
346: * The block layer relies on the fact that every driver can
347: * handle at lest a page worth of data per I/O, and needs the value
348: * aligned to the logical block size.
349: */
350: if (!lim->max_hw_sectors)
351: lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
352: if (WARN_ON_ONCE(lim->max_hw_sectors < PAGE_SECTORS))
353: return -EINVAL;
354: logical_block_sectors = lim->logical_block_size >> SECTOR_SHIFT;
355: if (WARN_ON_ONCE(logical_block_sectors > lim->max_hw_sectors))
356: return -EINVAL;
357: lim->max_hw_sectors = round_down(lim->max_hw_sectors,
358: logical_block_sectors);
359:
360: /*
361: * The actual max_sectors value is a complex beast and also takes the
362: * max_dev_sectors value (set by SCSI ULPs) and a user configurable
363: * value into account. The ->max_sectors value is always calculated
364: * from these, so directly setting it won't have any effect.
365: */
366: max_hw_sectors = min_not_zero(lim->max_hw_sectors,
367: lim->max_dev_sectors);
368: if (lim->max_user_sectors) {
369: if (lim->max_user_sectors < BLK_MIN_SEGMENT_SIZE / SECTOR_SIZE)
370: return -EINVAL;
371: lim->max_sectors = min(max_hw_sectors, lim->max_user_sectors);
372: } else if (lim->io_opt > (BLK_DEF_MAX_SECTORS_CAP << SECTOR_SHIFT)) {
373: lim->max_sectors =
374: min(max_hw_sectors, lim->io_opt >> SECTOR_SHIFT);
375: } else if (lim->io_min > (BLK_DEF_MAX_SECTORS_CAP << SECTOR_SHIFT)) {
376: lim->max_sectors =
377: min(max_hw_sectors, lim->io_min >> SECTOR_SHIFT);
378: } else {
379: lim->max_sectors = min(max_hw_sectors, BLK_DEF_MAX_SECTORS_CAP);
380: }
381: lim->max_sectors = round_down(lim->max_sectors,
382: logical_block_sectors);
383:
384: /*
385: * Random default for the maximum number of segments. Driver should not
386: * rely on this and set their own.
387: */
388: if (!lim->max_segments)
389: lim->max_segments = BLK_MAX_SEGMENTS;
390:
391: if (lim->max_hw_wzeroes_unmap_sectors &&
392: lim->max_hw_wzeroes_unmap_sectors != lim->max_write_zeroes_sectors)
393: return -EINVAL;
394: lim->max_wzeroes_unmap_sectors = min(lim->max_hw_wzeroes_unmap_sectors,
395: lim->max_user_wzeroes_unmap_sectors);
396:
397: lim->max_discard_sectors =
398: min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors);
399:
400: /*
401: * When discard is not supported, discard_granularity should be reported
402: * as 0 to userspace.
403: */
404: if (lim->max_discard_sectors)
405: lim->discard_granularity =
406: max(lim->discard_granularity, lim->physical_block_size);
407: else
408: lim->discard_granularity = 0;
409:
410: if (!lim->max_discard_segments)
411: lim->max_discard_segments = 1;
412:
413: /*
414: * By default there is no limit on the segment boundary alignment,
415: * but if there is one it can't be smaller than the page size as
416: * that would break all the normal I/O patterns.
417: */
418: if (!lim->seg_boundary_mask)
419: lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
420: if (WARN_ON_ONCE(lim->seg_boundary_mask < BLK_MIN_SEGMENT_SIZE - 1))
421: return -EINVAL;
422:
423: /*
424: * Stacking device may have both virtual boundary and max segment
425: * size limit, so allow this setting now, and long-term the two
426: * might need to move out of stacking limits since we have immutable
427: * bvec and lower layer bio splitting is supposed to handle the two
428: * correctly.
429: */
430: if (lim->virt_boundary_mask) {
431: if (!lim->max_segment_size)
432: lim->max_segment_size = UINT_MAX;
433: } else {
434: /*
435: * The maximum segment size has an odd historic 64k default that
436: * drivers probably should override. Just like the I/O size we
437: * require drivers to at least handle a full page per segment.
438: */
439: if (!lim->max_segment_size)
440: lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
441: if (WARN_ON_ONCE(lim->max_segment_size < BLK_MIN_SEGMENT_SIZE))
442: return -EINVAL;
443: }
444:
445: /* setup min segment size for building new segment in fast path */
446: if (lim->seg_boundary_mask > lim->max_segment_size - 1)
447: seg_size = lim->max_segment_size;
448: else
449: seg_size = lim->seg_boundary_mask + 1;
450: lim->min_segment_size = min_t(unsigned int, seg_size, PAGE_SIZE);
451:
452: /*
453: * We require drivers to at least do logical block aligned I/O, but
454: * historically could not check for that due to the separate calls
455: * to set the limits. Once the transition is finished the check
456: * below should be narrowed down to check the logical block size.
457: */
458: if (!lim->dma_alignment)
459: lim->dma_alignment = SECTOR_SIZE - 1;
460: if (WARN_ON_ONCE(lim->dma_alignment > PAGE_SIZE))
461: return -EINVAL;
462:
463: if (lim->alignment_offset) {
464: lim->alignment_offset &= (lim->physical_block_size - 1);
465: lim->flags &= ~BLK_FLAG_MISALIGNED;
466: }
467:
468: if (!(lim->features & BLK_FEAT_WRITE_CACHE))
469: lim->features &= ~BLK_FEAT_FUA;
470:
471: blk_validate_atomic_write_limits(lim);
472:
473: err = blk_validate_integrity_limits(lim);
474: if (err)
475: return err;
476: return blk_validate_zoned_limits(lim);
477: }
SourceFile:block/blk-settings.c]
|
| 32/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 21926
output: 21
thoughts: 589
Thoughts: **Debugging a Block Size Alignment Warning**
Okay, so I'm diving into this warning message. It's flagging an alignment issue in `blk_validate_limits` specifically with `blk_validate_block_size`. I know that `logical_block_size` is always a power of 2, constrained between 512 and `BLK_MAX_BLOCK_SIZE`, which is usually `PAGE_SIZE` or maybe up to 64KB. Now, if the `logical_block_size` *and* `block_size` are both powers of two, and `block_size` is greater than or equal to `logical_block_size`, then `block_size` *has* to be a multiple of `logical_block_size`. Therefore, `IS_ALIGNED(block_size, logical_block_size)` should *always* be true. So, why the heck is the warning triggering?
Let me double-check that warning message again: `WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))`. Right, `size` is getting passed to `__getblk_slow`. Where does `size` come from? Ah, tracing back, `__bread_gfp` calls `bdev_getblk`, and it passes in `size`. `sb_bread` calls `__bread_gfp`, passing in `sb->s_blocksize` as the `size` argument. So, `size` is essentially `sb->s_blocksize`.
Okay, so, `sb->s_blocksize` is the block size of the superblock. How could *that* not be aligned to `bdev_logical_block_size(bdev)`? That's really strange, it should just work...
Hold on... I'm missing something, there is a possibility that the block size could have changed. What if the `bdev_logical_block_size(bdev)` changed *after* `sb_set_blocksize` was called? That's a nasty race condition to consider. The reproducer mentions NBD! Ah-ha! NBD! This is a clue. The code snippet shows `ioctl` calls with `NBD_SET_SOCK` and `NBD_DO_IT`. NBD block size can be changed by the NBD server or by ioctl! That's the key. Let me go look up what `NBD_SET_BLKSIZE` does...
|
| 33/2 |
2026/05/31 01:52 |
tool |
grepper |
0m
Args: map[Expression:NBD_SET_BLKSIZE]
Results: map[Output:drivers/block/nbd.c=1582=static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
--
drivers/block/nbd.c-1595- return nbd_add_socket(nbd, arg, false);
drivers/block/nbd.c:1596: case NBD_SET_BLKSIZE:
drivers/block/nbd.c-1597- return nbd_set_size(nbd, config->bytesize, arg);
--
include/uapi/linux/nbd.h-23-#define NBD_SET_SOCK _IO( 0xab, 0 )
include/uapi/linux/nbd.h:24:#define NBD_SET_BLKSIZE _IO( 0xab, 1 )
include/uapi/linux/nbd.h-25-#define NBD_SET_SIZE _IO( 0xab, 2 )
]
|
| 34/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 23337
output: 38
thoughts: 75
Thoughts: **Analyzing the Reproducer and Block Size Configuration**
Okay, hold on a second. I need to re-evaluate what's happening in this reproducer. My initial understanding was off. The reproducer isn't directly calling `NBD_SET_BLKSIZE`, that's a key detail I missed. It's actually using `NBD_SET_SOCK` and then `NBD_DO_IT`. Right, that makes more sense in the context of how the NBD protocol is meant to work, since `NBD_DO_IT` connects to the server. And if it's connecting to the server, then *that* connection is where the block size could be negotiated or, more likely, determined! The server is the one that might communicate the block size. I'm going to dig into the `nbd_set_size` function, because I'm betting that's where the connection with the server is established and the actual block size gets sorted out. I should have considered that earlier.
|
| 35/2 |
2026/05/31 01:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_set_size]
Results: map[SourceCode: 334: static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
335: {
336: struct queue_limits lim;
337: int error;
338:
339: if (!blksize)
340: blksize = 1u << NBD_DEF_BLKSIZE_BITS;
341:
342: if (blk_validate_block_size(blksize))
343: return -EINVAL;
344:
345: if (bytesize < 0)
346: return -EINVAL;
347:
348: nbd->config->bytesize = bytesize;
349: nbd->config->blksize_bits = __ffs(blksize);
350:
351: if (!nbd->pid)
352: return 0;
353:
354: lim = queue_limits_start_update(nbd->disk->queue);
355: if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
356: lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
357: else
358: lim.max_hw_discard_sectors = 0;
359: if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
360: lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
361: } else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
362: lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
363: } else {
364: lim.features |= BLK_FEAT_WRITE_CACHE;
365: lim.features &= ~BLK_FEAT_FUA;
366: }
367: if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
368: lim.features |= BLK_FEAT_ROTATIONAL;
369: if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
370: lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;
371:
372: lim.logical_block_size = blksize;
373: lim.physical_block_size = blksize;
374: error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
375: if (error)
376: return error;
377:
378: if (max_part)
379: set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
380: if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
381: kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
382: return 0;
383: }
SourceFile:drivers/block/nbd.c]
|
| 36/2 |
2026/05/31 01:52 |
llm |
expert |
0m
Model:
Tokens:
input: 24569
output: 37
thoughts: 824
Thoughts: **Analyzing a Potential Filesystem Vulnerability**
Okay, so I'm digging into this code, and it's got me thinking. The `nbd_set_size` function seems to update queue limits, and crucially, it includes the `logical_block_size`. That's the key. If this function is called while a filesystem is mounted, the `bdev_logical_block_size(bdev)` could change unexpectedly.
But hold on, `nbd_set_size` calls `queue_limits_commit_update_frozen`. So, the queue gets frozen during the update. Does this mean the filesystem can't read during the brief freeze? No, it's just a temporary pause on the queue.
Okay, let's play this out: if `bdev_logical_block_size` changes, the filesystem's `sb->s_blocksize` might become misaligned! For example, if the superblock reports `s_blocksize` as 1024, but the underlying block device now reports a `bdev_logical_block_size` of 4096.
Let's do the math: `IS_ALIGNED(1024, 4096)` becomes `!(1024 & 4095)`. That's `!(1024)`, which is false. Boom! The warning gets triggered, that's the bug.
Is this a UDF-specific thing? No, any filesystem that uses `sb_bread` is potentially vulnerable if its underlying block device can change its logical block size, and that blocksize changes during a file system operation.
Now, a critical question: can a block device *actually* change its logical block size while it's mounted? Let's check how `nbd_set_size` can be called while mounted.
Looking at this reproducer, it mounts something like `/dev/nbd0` and then calls `NBD_DO_IT`, to connect the NBD device and run the protocol. The sequence seems to be:
```c
// fd_nbd = open("/dev/nbd#")
// sock = socket()
// fd_nbd2 = open("/dev/nbd#")
// ioctl(fd_nbd, NBD_SET_SOCK, sock)
// ioctl(fd_nbd2, NBD_DO_IT, 0)
// mount("/dev/nbd0", "./file1", "udf", ...)
```
Here's the problem: `NBD_DO_IT` seems to block until the NBD device is disconnected. But the reproducer calls mount concurrently?
No, wait, the reproducer is *single-threaded*! Looking at the system calls:
```c
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xab00, /*arg=*/r[1]);
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0);
syscall(__NR_mount, /*src=*/0x200000000000ul, /*dst=*/0x200000004a00ul, /*type=*/0x200000000080ul, /*flags=MS_LAZYTIME|MS_SILENT|MS_RDONLY|MS_NOSUID|MS_NODEV|0x80*/0x2008087ul, /*data=*/0ul);
```
If `NBD_DO_IT` is blocking, then mount wouldn't happen immediately! I see the issue, if `NBD_DO_IT` returns immediately because the socket isn't ready or it fails, the mount will succeed.
But, hang on, there's no `NBD_SET_BLKSIZE` or `NBD_SET_SIZE` called! Only `NBD_SET_SOCK`.
Wait a minute, what if the block size gets changed within `udf_fill_super` itself, before we even start the read? Okay, let's revisit that function. I need to understand if the superblock initialization messes with the block size.
|
| 37/2 |
2026/05/31 01:53 |
tool |
read-file |
0m
Args: map[File:fs/udf/super.c FirstLine:2195 LineCount:30]
Results: map[Contents:2195:
2196: if (uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)) {
2197: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2198: } else {
2199: uopt->blocksize = bdev_logical_block_size(sb->s_bdev);
2200: while (uopt->blocksize <= 4096) {
2201: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2202: if (ret < 0) {
2203: if (!silent && ret != -EACCES) {
2204: pr_notice("Scanning with blocksize %u failed\n",
2205: uopt->blocksize);
2206: }
2207: brelse(sbi->s_lvid_bh);
2208: sbi->s_lvid_bh = NULL;
2209: /*
2210: * EACCES is special - we want to propagate to
2211: * upper layers that we cannot handle RW mount.
2212: */
2213: if (ret == -EACCES)
2214: break;
2215: } else
2216: break;
2217:
2218: uopt->blocksize <<= 1;
2219: }
2220: }
2221: if (ret < 0) {
2222: if (ret == -EAGAIN) {
2223: udf_warn(sb, "No partition found (1)\n");
2224: ret = -EINVAL;
]
|
| 38/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 26847
output: 34
thoughts: 501
Thoughts: **Analyzing `udf_fill_super` and Block Size Handling**
Okay, so `udf_fill_super` is playing around with block sizes, interesting. It kicks things off with the device's *logical* block size using `bdev_logical_block_size` and sets that to `uopt->blocksize`. Then it dives into `udf_load_vrs`, and crucially, calls `sb_set_blocksize(sb, uopt->blocksize)`. If that fails, it doubles `uopt->blocksize` and tries again.
Aha, so `sb_set_blocksize` is updating `sb->s_blocksize` to the *larger* block size in each attempt. This means `udf_load_vrs` is actually reading blocks with the *updated* block size after a failure. But what's going on under the hood with that `sb_set_blocksize`? It's calling `set_blocksize(sb->s_bdev_file, size)`.
Okay, does `set_blocksize` *change* `bdev_logical_block_size(bdev)`? No, it doesn't. That one's fixed, it's just the device's reported logical block size. `set_blocksize` is changing something else: the `inode->i_blkbits` of the block device's inode. That makes sense. It's not the *physical* block size, it's the *filesystem's* view of the block size.
So, even if `uopt->blocksize` is larger than the *device's* logical block size, as long as it's a multiple (which it always will be since the doubling), `IS_ALIGNED(uopt->blocksize, bdev_logical_block_size(bdev))` should still be true. But what about that edge case I was worried about? What if the device's `bdev_logical_block_size(bdev)` *isn't* a power of 2? Ah, right. `blk_validate_limits` enforces that it *is* a power of 2, so that's handled. Good.
Okay, let's circle back. What if `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)` is set? That's the user-specified block size via the `bs=` mount option. Okay, so now the user can specify a blocksize, let's say `bs=512`, and the device has `bdev_logical_block_size(bdev)` as 1024. Then `sb_set_blocksize` is called with 512. Let me re-examine `sb_set_blocksize` and consider this case more carefully...
|
| 39/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:set_blocksize]
Results: map[SourceCode: 178: int set_blocksize(struct file *file, int size)
179: {
180: struct inode *inode = file->f_mapping->host;
181: struct block_device *bdev = I_BDEV(inode);
182: int ret;
183:
184: ret = bdev_validate_blocksize(bdev, size);
185: if (ret)
186: return ret;
187:
188: if (!file->private_data)
189: return -EINVAL;
190:
191: /* Don't change the size if it is same as current */
192: if (inode->i_blkbits != blksize_bits(size)) {
193: /*
194: * Flush and truncate the pagecache before we reconfigure the
195: * mapping geometry because folio sizes are variable now. If a
196: * reader has already allocated a folio whose size is smaller
197: * than the new min_order but invokes readahead after the new
198: * min_order becomes visible, readahead will think there are
199: * "zero" blocks per folio and crash. Take the inode and
200: * invalidation locks to avoid racing with
201: * read/write/fallocate.
202: */
203: inode_lock(inode);
204: filemap_invalidate_lock(inode->i_mapping);
205:
206: sync_blockdev(bdev);
207: kill_bdev(bdev);
208:
209: inode->i_blkbits = blksize_bits(size);
210: mapping_set_folio_min_order(inode->i_mapping, get_order(size));
211: kill_bdev(bdev);
212: filemap_invalidate_unlock(inode->i_mapping);
213: inode_unlock(inode);
214: }
215: return 0;
216: }
SourceFile:block/bdev.c]
|
| 40/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 28615
output: 37
thoughts: 22
Thoughts: Here's my summary, as though I'm thinking through this process:
**Validating Block Size in `set_blocksize`**
Okay, so I'm looking at `set_blocksize`. The first thing that jumps out is the call to `bdev_validate_blocksize(bdev, size)`. Right, so this is where the *real* validation happens. `set_blocksize` itself is just the entry point, but it delegates the heavy lifting of verifying the proposed block size against the characteristics of the block device (`bdev`) to this dedicated function. I'd expect `bdev_validate_blocksize` to check things like: does the `size` even make sense? Is it a power of two? Does it fall within the acceptable ranges for this particular block device? Does the device *support* this block size? It's the gatekeeper, ensuring we don't end up with an invalid or unsupported configuration further down the line. I need to dig into the implementation of `bdev_validate_blocksize` next to see exactly what checks are being performed. That's where the critical logic resides.
|
| 41/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:bdev_validate_blocksize]
Results: map[SourceCode: 155: /**
156: * bdev_validate_blocksize - check that this block size is acceptable
157: * @bdev: blockdevice to check
158: * @block_size: block size to check
159: *
160: * For block device users that do not use buffer heads or the block device
161: * page cache, make sure that this block size can be used with the device.
162: *
163: * Return: On success zero is returned, negative error code on failure.
164: */
165: int bdev_validate_blocksize(struct block_device *bdev, int block_size)
166: {
167: if (blk_validate_block_size(block_size))
168: return -EINVAL;
169:
170: /* Size cannot be smaller than the size supported by the device */
171: if (block_size < bdev_logical_block_size(bdev))
172: return -EINVAL;
173:
174: return 0;
175: }
SourceFile:block/bdev.c]
|
| 42/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 29264
output: 39
thoughts: 219
Thoughts: **Analyzing Block Size Validation**
Okay, so I'm diving into this block size validation routine. It looks like `bdev_validate_blocksize` kicks things off, and the first thing it does is ensure the requested `block_size` isn't smaller than the device's logical block size, right? That makes sense; you can't read or write less than the smallest unit. Then `blk_validate_block_size` gets involved, and this one makes sure the size is a power of 2. So, combining those two constraints: the `size` *has* to be a power of 2, AND it has to be greater than or equal to the device's logical block size, which is itself, also, a power of 2.
Given that, it's immediately clear to me that `size` absolutely *must* be a multiple of `bdev_logical_block_size(bdev)`. That has to be true. Which is what that `IS_ALIGNED` macro is really doing... checking that the `size` is a multiple of the logical block size. It's a fundamental constraint for any block-based storage.
But hold on, am I missing something? Are there any odd corner cases? Am I assuming that the logical block size is *always* a power of 2? Hmm, gotta verify. Let me double-check how `blk_validate_block_size` handles things. Just to be completely certain.
|
| 43/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/blkdev.h Name:blk_validate_block_size]
Results: map[SourceCode: 284: /* blk_validate_limits() validates bsize, so drivers don't usually need to */
285: static inline int blk_validate_block_size(unsigned long bsize)
286: {
287: if (bsize < 512 || bsize > BLK_MAX_BLOCK_SIZE || !is_power_of_2(bsize))
288: return -EINVAL;
289:
290: return 0;
291: }
SourceFile:include/linux/blkdev.h]
|
| 44/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 30006
output: 36
thoughts: 252
Thoughts: **My Concerns Regarding Block Size Changes**
Okay, first things first, I see the code is checking if the block size (`bsize`) isn't a power of 2: `!is_power_of_2(bsize)`. That makes sense. However, I have a nagging concern. What happens if the `bdev_logical_block_size(bdev)` changes *after* `sb_set_blocksize` has been called? That would be a serious problem!
I'm thinking now about how that could happen, and it strikes me: `nbd_set_size` is called concurrently, and it *can* modify the `logical_block_size`. So, I need to check whether `nbd_set_size` can be invoked while the device is mounted.
Right, I need to check where `nbd_set_size` is called from. Ah, it comes from `__nbd_ioctl`, specifically when handling `NBD_SET_BLKSIZE` or `NBD_SET_SIZE` ioctls. The critical question here is whether `__nbd_ioctl` is properly protected against concurrent mounts. I need to know if the mount itself is exclusive.
To address that, let me think about how the block device is opened when mounting. `blkdev_get_by_path` will open it exclusively if `FMODE_EXCL` is passed, but does the mount call use that flag? No, it uses `bdev_file_open_by_path`, which might use `FMODE_EXCL` if it is the first mount on the device.
But hang on, this is worse than I thought! `nbd_ioctl` *doesn't* appear to check if the device is exclusively opened! This is a potential race condition! I need to dig into the `nbd_ioctl` code. Now.
|
| 45/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_ioctl]
Results: map[SourceCode:1629: static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
1630: unsigned int cmd, unsigned long arg)
1631: {
1632: struct nbd_device *nbd = bdev->bd_disk->private_data;
1633: struct nbd_config *config = nbd->config;
1634: int error = -EINVAL;
1635:
1636: if (!capable(CAP_SYS_ADMIN))
1637: return -EPERM;
1638:
1639: /* The block layer will pass back some non-nbd ioctls in case we have
1640: * special handling for them, but we don't so just return an error.
1641: */
1642: if (_IOC_TYPE(cmd) != 0xab)
1643: return -EINVAL;
1644:
1645: mutex_lock(&nbd->config_lock);
1646:
1647: /* Don't allow ioctl operations on a nbd device that was created with
1648: * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
1649: */
1650: if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
1651: (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
1652: error = __nbd_ioctl(bdev, nbd, cmd, arg);
1653: else
1654: dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
1655: mutex_unlock(&nbd->config_lock);
1656: return error;
1657: }
SourceFile:drivers/block/nbd.c]
|
| 46/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 31228
output: 23
thoughts: 373
Thoughts: **Analyzing the NBD Reproducer**
Okay, first things first, I see that the `nbd_ioctl` call requires `CAP_SYS_ADMIN`, which is expected. But the reproducer is running as root, so that's not a blocker. I need to understand the data flow. The reproducer calls `NBD_DO_IT`, which means it’s connecting to the NBD server.
Now, does the server have the ability to send the block size? I need to check the `nbd.c` code, specifically around `nbd_size_set` or similar functions. Ah, right, NBD block size can indeed be negotiated during `NBD_DO_IT`... or can it? Let me think... No, that's wrong. `NBD_DO_IT` just launches the threads; the block size negotiation is actually done in userspace *before* the call to `NBD_DO_IT`.
Hold on... I need to double-check the reproducer. It’s critical I understand this. Wait, `NBD_SET_BLKSIZE` is *not* called in the reproducer! Let's examine the C code more closely:
```c
// ioctl$NBD_SET_SOCK arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab00 (4 bytes)
// arg: sock_nbd_client (resource)
// ]
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xab00, /*arg=*/r[1]);
// ioctl$NBD_DO_IT arguments: [
// fd: fd_nbd (resource)
// cmd: const = 0xab03 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0);
```
Okay, I see it. `NBD_SET_BLKSIZE` is definitely *not* being called. So the block size isn't being explicitly set. It's using the default. Which means the next logical question is: what is the *default* block size for NBD? That's the key.
|
| 47/2 |
2026/05/31 01:53 |
tool |
grepper |
0m
Args: map[Expression:NBD_DEF_BLKSIZE_BITS]
Results: map[Output:drivers/block/nbd.c=160=static struct dentry *nbd_dbg_dir;
--
drivers/block/nbd.c-164-
drivers/block/nbd.c:165:#define NBD_DEF_BLKSIZE_BITS 10
drivers/block/nbd.c-166-
--
drivers/block/nbd.c=334=static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
--
drivers/block/nbd.c-339- if (!blksize)
drivers/block/nbd.c:340: blksize = 1u << NBD_DEF_BLKSIZE_BITS;
drivers/block/nbd.c-341-
--
drivers/block/nbd.c=1659=static int nbd_alloc_and_init_config(struct nbd_device *nbd)
--
drivers/block/nbd.c-1677- init_waitqueue_head(&config->conn_wait);
drivers/block/nbd.c:1678: config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
drivers/block/nbd.c-1679- atomic_set(&config->live_connections, 0);
]
|
| 48/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 32469
output: 42
thoughts: 231
Thoughts: **Investigating a Potential Block Size Misalignment**
Okay, so I'm digging into this UDF filesystem code and something's not quite right. The default block size, as I understand it, is `1 << 10`, which equals 1024. That should mean the logical block size returned by `bdev_logical_block_size(bdev)` should also be 1024, right? And indeed, `udf_fill_super` sets `uopt->blocksize = 1024`. Then, it calls `udf_load_vrs`, which, as expected, calls `sb_set_blocksize(sb, 1024)`.
Now, `udf_load_vrs` goes on to read blocks, as it should. The thing is, if `bdev_logical_block_size(bdev)` is 1024, and the superblock's `sb->s_blocksize` is also 1024, then the alignment check `IS_ALIGNED(1024, 1024)` should be *true*, and this warning should not be triggering. That's the crux of my investigation.
Why is this warning being generated? What am I missing here?
The only reasonable scenario that comes to mind is that `bdev_logical_block_size(bdev)` is NOT 1024. Could it be 512? I need to check how the block device is being initialized, where that value is actually coming from. Let me go check `nbd_alloc_and_init_config`.
|
| 49/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_alloc_and_init_config]
Results: map[SourceCode:1659: static int nbd_alloc_and_init_config(struct nbd_device *nbd)
1660: {
1661: struct nbd_config *config;
1662:
1663: if (WARN_ON(nbd->config))
1664: return -EINVAL;
1665:
1666: if (!try_module_get(THIS_MODULE))
1667: return -ENODEV;
1668:
1669: config = kzalloc(sizeof(struct nbd_config), GFP_NOFS);
1670: if (!config) {
1671: module_put(THIS_MODULE);
1672: return -ENOMEM;
1673: }
1674:
1675: atomic_set(&config->recv_threads, 0);
1676: init_waitqueue_head(&config->recv_wq);
1677: init_waitqueue_head(&config->conn_wait);
1678: config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
1679: atomic_set(&config->live_connections, 0);
1680:
1681: nbd->config = config;
1682: /*
1683: * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
1684: * its pair is the barrier in nbd_get_config_unlocked().
1685: * So nbd_get_config_unlocked() won't see nbd->config as null after
1686: * refcount_inc_not_zero() succeed.
1687: */
1688: smp_mb__before_atomic();
1689: refcount_set(&nbd->config_refs, 1);
1690:
1691: return 0;
1692: }
SourceFile:drivers/block/nbd.c]
|
| 50/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 33651
output: 38
thoughts: 38
Thoughts: Okay, let's see...
**Analyzing `config->blksize_bits` and its Impact**
Hmm, so `config->blksize_bits` is set to 10. That's a block size of 1024 bytes, right? But the real question is, does this setting *actually* influence the queue limits? I need to make sure this isn't just a configuration setting that's not being used correctly. It's a common oversight, and I've seen it before, so I should double-check.
Let's not jump to conclusions. I need to trace this back to the source. The critical piece here is probably how the NBD disk is added. So, let me look into the `nbd_add_disk` function. That's where I'll probably find how the block size is translated into queue parameters, or where I can confirm if there's no actual link between the config parameter and the final disk setup. Let's see if this influences queue depth or any related parameters.
|
| 51/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_add_disk]
Results: map[SourceCode: SourceFile:]
|
| 52/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 33971
output: 21
thoughts: 15
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Investigating Block Device Allocation**
Okay, so we've hit an issue. Time to dig in. My gut tells me this feels like a potential problem in the block device allocation routines. I need to understand how we're assigning the physical backing store to the NBD (Network Block Device) layer. My immediate thought is to start with a look at `nbd_alloc_disk`, or something functionally similar within our codebase. It could be a custom implementation, but the core logic of allocating the device representation is likely centralized somewhere. I need to trace the path of disk allocation. I'll need to figure out where we're falling down on assignment of resources.
|
| 53/2 |
2026/05/31 01:53 |
tool |
grepper |
0m
Args: map[Expression:blk_mq_alloc_disk]
Results: map[Output:arch/um/drivers/ubd_kern.c=829=static int ubd_add(int n, char **error_out)
--
arch/um/drivers/ubd_kern.c-874-
arch/um/drivers/ubd_kern.c:875: disk = blk_mq_alloc_disk(&ubd_dev->tag_set, &lim, ubd_dev);
arch/um/drivers/ubd_kern.c-876- if (IS_ERR(disk)) {
--
block/blk-mq.c=4438=EXPORT_SYMBOL(blk_mq_destroy_queue);
block/blk-mq.c-4439-
block/blk-mq.c:4440:struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set,
block/blk-mq.c-4441- struct queue_limits *lim, void *queuedata,
--
block/blk-mq.c-4459-}
block/blk-mq.c:4460:EXPORT_SYMBOL(__blk_mq_alloc_disk);
block/blk-mq.c-4461-
block/blk-mq.c:4462:struct gendisk *blk_mq_alloc_disk_for_queue(struct request_queue *q,
block/blk-mq.c-4463- struct lock_class_key *lkclass)
--
block/blk-mq.c-4473-}
block/blk-mq.c:4474:EXPORT_SYMBOL(blk_mq_alloc_disk_for_queue);
block/blk-mq.c-4475-
--
drivers/block/amiflop.c=1778=static int fd_alloc_disk(int drive, int system)
--
drivers/block/amiflop.c-1785-
drivers/block/amiflop.c:1786: disk = blk_mq_alloc_disk(&unit[drive].tag_set, &lim, NULL);
drivers/block/amiflop.c-1787- if (IS_ERR(disk))
--
drivers/block/aoe/aoeblk.c=324=static const struct blk_mq_ops aoeblk_mq_ops = {
--
drivers/block/aoe/aoeblk.c-327-
drivers/block/aoe/aoeblk.c:328:/* blk_mq_alloc_disk and add_disk can sleep */
drivers/block/aoe/aoeblk.c-329-void
drivers/block/aoe/aoeblk.c=330=aoeblk_gdalloc(void *vp)
--
drivers/block/aoe/aoeblk.c-377-
drivers/block/aoe/aoeblk.c:378: gd = blk_mq_alloc_disk(set, &lim, d);
drivers/block/aoe/aoeblk.c-379- if (IS_ERR(gd)) {
--
drivers/block/ataflop.c=1994=static int ataflop_alloc_disk(unsigned int drive, unsigned int type)
--
drivers/block/ataflop.c-2000-
drivers/block/ataflop.c:2001: disk = blk_mq_alloc_disk(&unit[drive].tag_set, &lim, NULL);
drivers/block/ataflop.c-2002- if (IS_ERR(disk))
--
drivers/block/floppy.c=4516=static int floppy_alloc_disk(unsigned int drive, unsigned int type)
--
drivers/block/floppy.c-4523-
drivers/block/floppy.c:4524: disk = blk_mq_alloc_disk(&tag_sets[drive], &lim, NULL);
drivers/block/floppy.c-4525- if (IS_ERR(disk))
--
drivers/block/loop.c=1993=static int loop_add(int i)
--
drivers/block/loop.c-2042-
drivers/block/loop.c:2043: disk = lo->lo_disk = blk_mq_alloc_disk(&lo->tag_set, &lim, lo);
drivers/block/loop.c-2044- if (IS_ERR(disk)) {
--
drivers/block/mtip32xx/mtip32xx.c=3399=static int mtip_block_initialize(struct driver_data *dd)
--
drivers/block/mtip32xx/mtip32xx.c-3435-
drivers/block/mtip32xx/mtip32xx.c:3436: dd->disk = blk_mq_alloc_disk(&dd->tags, &lim, dd);
drivers/block/mtip32xx/mtip32xx.c-3437- if (IS_ERR(dd->disk)) {
--
drivers/block/nbd.c=1896=static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
--
drivers/block/nbd.c-1942-
drivers/block/nbd.c:1943: disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
drivers/block/nbd.c-1944- if (IS_ERR(disk)) {
--
drivers/block/null_blk/main.c=1946=static int null_add_dev(struct nullb_device *dev)
--
drivers/block/null_blk/main.c-1997-
drivers/block/null_blk/main.c:1998: nullb->disk = blk_mq_alloc_disk(nullb->tag_set, &lim, nullb);
drivers/block/null_blk/main.c-1999- if (IS_ERR(nullb->disk)) {
--
drivers/block/ps3disk.c=379=static int ps3disk_probe(struct ps3_system_bus_device *_dev)
--
drivers/block/ps3disk.c-440-
drivers/block/ps3disk.c:441: gendisk = blk_mq_alloc_disk(&priv->tag_set, &lim, dev);
drivers/block/ps3disk.c-442- if (IS_ERR(gendisk)) {
drivers/block/ps3disk.c:443: dev_err(&dev->sbd.core, "%s:%u: blk_mq_alloc_disk failed\n",
drivers/block/ps3disk.c-444- __func__, __LINE__);
--
drivers/block/rbd.c=4949=static int rbd_init_disk(struct rbd_device *rbd_dev)
--
drivers/block/rbd.c-4982-
drivers/block/rbd.c:4983: disk = blk_mq_alloc_disk(&rbd_dev->tag_set, &lim, rbd_dev);
drivers/block/rbd.c-4984- if (IS_ERR(disk)) {
--
drivers/block/rnbd/rnbd-clt.c=1361=static int rnbd_client_setup_device(struct rnbd_clt_dev *dev,
--
drivers/block/rnbd/rnbd-clt.c-1392-
drivers/block/rnbd/rnbd-clt.c:1393: dev->gd = blk_mq_alloc_disk(&dev->sess->tag_set, &lim, dev);
drivers/block/rnbd/rnbd-clt.c-1394- if (IS_ERR(dev->gd))
--
drivers/block/sunvdc.c=785=static int probe_disk(struct vdc_port *port)
--
drivers/block/sunvdc.c-835-
drivers/block/sunvdc.c:836: g = blk_mq_alloc_disk(&port->tag_set, &lim, port);
drivers/block/sunvdc.c-837- if (IS_ERR(g)) {
--
drivers/block/swim.c=788=static int swim_floppy_init(struct swim_priv *swd)
--
drivers/block/swim.c-825- swd->unit[drive].disk =
drivers/block/swim.c:826: blk_mq_alloc_disk(&swd->unit[drive].tag_set, &lim,
drivers/block/swim.c-827- &swd->unit[drive]);
--
drivers/block/swim3.c=1190=static int swim3_attach(struct macio_dev *mdev,
--
drivers/block/swim3.c-1215-
drivers/block/swim3.c:1216: disk = blk_mq_alloc_disk(&fs->tag_set, &lim, fs);
drivers/block/swim3.c-1217- if (IS_ERR(disk)) {
--
drivers/block/ublk_drv.c=2855=static int ublk_ctrl_start_dev(struct ublk_device *ub,
--
drivers/block/ublk_drv.c-2932-
drivers/block/ublk_drv.c:2933: disk = blk_mq_alloc_disk(&ub->tag_set, &lim, NULL);
drivers/block/ublk_drv.c-2934- if (IS_ERR(disk)) {
--
drivers/block/virtio_blk.c=1430=static int virtblk_probe(struct virtio_device *vdev)
--
drivers/block/virtio_blk.c-1501-
drivers/block/virtio_blk.c:1502: vblk->disk = blk_mq_alloc_disk(&vblk->tag_set, &lim, vblk);
drivers/block/virtio_blk.c-1503- if (IS_ERR(vblk->disk)) {
--
drivers/block/xen-blkfront.c=1072=static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
--
drivers/block/xen-blkfront.c-1141- blkif_set_queue_limits(info, &lim);
drivers/block/xen-blkfront.c:1142: gd = blk_mq_alloc_disk(&info->tag_set, &lim, info);
drivers/block/xen-blkfront.c-1143- if (IS_ERR(gd)) {
--
drivers/block/z2ram.c=316=static int z2ram_register_disk(int minor)
--
drivers/block/z2ram.c-320-
drivers/block/z2ram.c:321: disk = blk_mq_alloc_disk(&tag_set, NULL, NULL);
drivers/block/z2ram.c-322- if (IS_ERR(disk))
--
drivers/block/zloop.c=883=static int zloop_ctl_add(struct zloop_options *opts)
--
drivers/block/zloop.c-992-
drivers/block/zloop.c:993: zlo->disk = blk_mq_alloc_disk(&zlo->tag_set, &lim, zlo);
drivers/block/zloop.c-994- if (IS_ERR(zlo->disk)) {
drivers/block/zloop.c:995: pr_err("blk_mq_alloc_disk failed (err=%d)\n", ret);
drivers/block/zloop.c-996- ret = PTR_ERR(zlo->disk);
--
drivers/cdrom/gdrom.c=739=static int probe_gdrom(struct platform_device *devptr)
--
drivers/cdrom/gdrom.c-783-
drivers/cdrom/gdrom.c:784: gd.disk = blk_mq_alloc_disk(&gd.tag_set, &lim, NULL);
drivers/cdrom/gdrom.c-785- if (IS_ERR(gd.disk)) {
--
drivers/memstick/core/ms_block.c=2078=static int msb_init_disk(struct memstick_dev *card)
--
drivers/memstick/core/ms_block.c-2100-
drivers/memstick/core/ms_block.c:2101: msb->disk = blk_mq_alloc_disk(&msb->tag_set, &lim, card);
drivers/memstick/core/ms_block.c-2102- if (IS_ERR(msb->disk)) {
--
drivers/memstick/core/mspro_block.c=1101=static int mspro_block_init_disk(struct memstick_dev *card)
--
drivers/memstick/core/mspro_block.c-1143-
drivers/memstick/core/mspro_block.c:1144: msb->disk = blk_mq_alloc_disk(&msb->tag_set, &lim, card);
drivers/memstick/core/mspro_block.c-1145- if (IS_ERR(msb->disk)) {
--
drivers/mmc/core/queue.c=346=static struct gendisk *mmc_alloc_disk(struct mmc_queue *mq,
--
drivers/mmc/core/queue.c-383-
drivers/mmc/core/queue.c:384: disk = blk_mq_alloc_disk(&mq->tag_set, &lim, mq);
drivers/mmc/core/queue.c-385- if (IS_ERR(disk))
--
drivers/mtd/mtd_blkdevs.c=276=int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
--
drivers/mtd/mtd_blkdevs.c-342- /* Create gendisk */
drivers/mtd/mtd_blkdevs.c:343: gd = blk_mq_alloc_disk(new->tag_set, &lim, new);
drivers/mtd/mtd_blkdevs.c-344- if (IS_ERR(gd)) {
--
drivers/mtd/ubi/block.c=349=int ubiblock_create(struct ubi_volume_info *vi)
--
drivers/mtd/ubi/block.c-399- /* Initialize the gendisk of this ubiblock device */
drivers/mtd/ubi/block.c:400: gd = blk_mq_alloc_disk(&dev->tag_set, &lim, dev);
drivers/mtd/ubi/block.c-401- if (IS_ERR(gd)) {
--
drivers/nvme/host/core.c=4099=static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
--
drivers/nvme/host/core.c-4116-
drivers/nvme/host/core.c:4117: disk = blk_mq_alloc_disk(ctrl->tagset, &lim, ns);
drivers/nvme/host/core.c-4118- if (IS_ERR(disk))
--
drivers/s390/block/dasd_genhd.c=35=int dasd_gendisk_alloc(struct dasd_block *block)
--
drivers/s390/block/dasd_genhd.c-63-
drivers/s390/block/dasd_genhd.c:64: gdp = blk_mq_alloc_disk(&block->tag_set, &lim, block);
drivers/s390/block/dasd_genhd.c-65- if (IS_ERR(gdp)) {
--
drivers/s390/block/scm_blk.c=436=int scm_blk_dev_setup(struct scm_blk_dev *bdev, struct scm_device *scmdev)
--
drivers/s390/block/scm_blk.c-469-
drivers/s390/block/scm_blk.c:470: bdev->gendisk = blk_mq_alloc_disk(&bdev->tag_set, &lim, scmdev);
drivers/s390/block/scm_blk.c-471- if (IS_ERR(bdev->gendisk)) {
--
drivers/scsi/sd.c=3910=static int sd_probe(struct device *dev)
--
drivers/scsi/sd.c-3939-
drivers/scsi/sd.c:3940: gd = blk_mq_alloc_disk_for_queue(sdp->request_queue,
drivers/scsi/sd.c-3941- &sd_bio_compl_lkclass);
--
drivers/scsi/sr.c=611=static int sr_probe(struct device *dev)
--
drivers/scsi/sr.c-627-
drivers/scsi/sr.c:628: disk = blk_mq_alloc_disk_for_queue(sdev->request_queue,
drivers/scsi/sr.c-629- &sr_bio_compl_lkclass);
--
include/linux/blk-mq.h=696=enum {
--
include/linux/blk-mq.h-705-
include/linux/blk-mq.h:706:struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set,
include/linux/blk-mq.h-707- struct queue_limits *lim, void *queuedata,
include/linux/blk-mq.h-708- struct lock_class_key *lkclass);
include/linux/blk-mq.h:709:#define blk_mq_alloc_disk(set, lim, queuedata) \
include/linux/blk-mq.h-710-({ \
--
include/linux/blk-mq.h-712- \
include/linux/blk-mq.h:713: __blk_mq_alloc_disk(set, lim, queuedata, &__key); \
include/linux/blk-mq.h-714-})
include/linux/blk-mq.h:715:struct gendisk *blk_mq_alloc_disk_for_queue(struct request_queue *q,
include/linux/blk-mq.h-716- struct lock_class_key *lkclass);
--
rust/kernel/block/mq/gen_disk.rs=91= pub fn build<T: Operations>(
--
rust/kernel/block/mq/gen_disk.rs-106- let gendisk = from_err_ptr(unsafe {
rust/kernel/block/mq/gen_disk.rs:107: bindings::__blk_mq_alloc_disk(
rust/kernel/block/mq/gen_disk.rs-108- tagset.raw_tag_set(),
]
|
| 54/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 39010
output: 38
thoughts: 30
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deeply familiar with block device drivers and the Linux kernel:
**Dissecting the NBD Device Addition**
Alright, I'm diving into the `nbd_dev_add` function. The first thing that jumps out is its call to `blk_mq_alloc_disk`. This immediately signals that the Network Block Device (NBD) driver is, at its core, utilizing the blk-mq (block multi-queue) framework for its I/O operations. Given that blk-mq is the modern, preferred method, it is no surprise and makes sense that the driver takes this approach. I need to understand how the NBD device is actually being integrated into the blk-mq system. I should begin my investigation with `nbd_dev_add` itself, since that's where the initial connection to the block layer is made. This allocation of the `disk` structure is critical as it represents the fundamental representation of the device within the kernel's block I/O subsystem. Let's see how that happens.
|
| 55/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_dev_add]
Results: map[SourceCode:1896: static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
1897: {
1898: struct queue_limits lim = {
1899: .max_hw_sectors = 65536,
1900: .io_opt = 256 << SECTOR_SHIFT,
1901: .max_segments = USHRT_MAX,
1902: .max_segment_size = UINT_MAX,
1903: };
1904: struct nbd_device *nbd;
1905: struct gendisk *disk;
1906: int err = -ENOMEM;
1907:
1908: nbd = kzalloc(sizeof(struct nbd_device), GFP_KERNEL);
1909: if (!nbd)
1910: goto out;
1911:
1912: nbd->tag_set.ops = &nbd_mq_ops;
1913: nbd->tag_set.nr_hw_queues = 1;
1914: nbd->tag_set.queue_depth = 128;
1915: nbd->tag_set.numa_node = NUMA_NO_NODE;
1916: nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
1917: nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
1918: nbd->tag_set.driver_data = nbd;
1919: INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
1920: nbd->backend = NULL;
1921:
1922: err = blk_mq_alloc_tag_set(&nbd->tag_set);
1923: if (err)
1924: goto out_free_nbd;
1925:
1926: mutex_lock(&nbd_index_mutex);
1927: if (index >= 0) {
1928: err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
1929: GFP_KERNEL);
1930: if (err == -ENOSPC)
1931: err = -EEXIST;
1932: } else {
1933: err = idr_alloc(&nbd_index_idr, nbd, 0,
1934: (MINORMASK >> part_shift) + 1, GFP_KERNEL);
1935: if (err >= 0)
1936: index = err;
1937: }
1938: nbd->index = index;
1939: mutex_unlock(&nbd_index_mutex);
1940: if (err < 0)
1941: goto out_free_tags;
1942:
1943: disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
1944: if (IS_ERR(disk)) {
1945: err = PTR_ERR(disk);
1946: goto out_free_idr;
1947: }
1948: nbd->disk = disk;
1949:
1950: nbd->recv_workq = alloc_workqueue("nbd%d-recv",
1951: WQ_MEM_RECLAIM | WQ_HIGHPRI |
1952: WQ_UNBOUND, 0, nbd->index);
1953: if (!nbd->recv_workq) {
1954: dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
1955: err = -ENOMEM;
1956: goto out_err_disk;
1957: }
1958:
1959: mutex_init(&nbd->config_lock);
1960: refcount_set(&nbd->config_refs, 0);
1961: /*
1962: * Start out with a zero references to keep other threads from using
1963: * this device until it is fully initialized.
1964: */
1965: refcount_set(&nbd->refs, 0);
1966: INIT_LIST_HEAD(&nbd->list);
1967: disk->major = NBD_MAJOR;
1968: disk->first_minor = index << part_shift;
1969: disk->minors = 1 << part_shift;
1970: disk->fops = &nbd_fops;
1971: disk->private_data = nbd;
1972: sprintf(disk->disk_name, "nbd%d", index);
1973: err = add_disk(disk);
1974: if (err)
1975: goto out_free_work;
1976:
1977: /*
1978: * Now publish the device.
1979: */
1980: refcount_set(&nbd->refs, refs);
1981: nbd_total_devices++;
1982: return nbd;
1983:
1984: out_free_work:
1985: destroy_workqueue(nbd->recv_workq);
1986: out_err_disk:
1987: put_disk(disk);
1988: out_free_idr:
1989: mutex_lock(&nbd_index_mutex);
1990: idr_remove(&nbd_index_idr, index);
1991: mutex_unlock(&nbd_index_mutex);
1992: out_free_tags:
1993: blk_mq_free_tag_set(&nbd->tag_set);
1994: out_free_nbd:
1995: kfree(nbd);
1996: out:
1997: return ERR_PTR(err);
1998: }
SourceFile:drivers/block/nbd.c]
|
| 56/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 40998
output: 40
thoughts: 204
Thoughts: **Analyzing the Block Size Confusion**
Okay, hold on a second. It just hit me: `lim` *doesn't* actually define the `logical_block_size`! That's a key detail I missed initially. So, if I'm understanding this correctly, `blk_validate_limits` is going to default `lim->logical_block_size` to `SECTOR_SIZE`, which means it's setting it to 512 bytes. Right, so that means `bdev_logical_block_size(bdev)` is *initially* 512!
But hang on, there's `nbd_set_size`, and that's the part that's throwing me. It looks like `nbd_set_size` sets it to `1 << NBD_DEF_BLKSIZE_BITS`, which would be 1024 bytes, but *only* if `blksize` is zero. So when is `nbd_set_size` even *called*?
Ah, got it. It looks like `nbd_set_size` is called inside `__nbd_ioctl` *only* for `NBD_SET_BLKSIZE`. But the reproducer code doesn't explicitly make an `NBD_SET_BLKSIZE` call, does it? No, it doesn't.
Now, does something in the `NBD_DO_IT` path call `nbd_set_size`? Let me check `nbd_start_device_ioctl`...
|
| 57/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_start_device_ioctl]
Results: map[SourceCode:1532: static int nbd_start_device_ioctl(struct nbd_device *nbd)
1533: {
1534: struct nbd_config *config = nbd->config;
1535: int ret;
1536:
1537: ret = nbd_start_device(nbd);
1538: if (ret)
1539: return ret;
1540:
1541: if (max_part)
1542: set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
1543: mutex_unlock(&nbd->config_lock);
1544: ret = wait_event_interruptible(config->recv_wq,
1545: atomic_read(&config->recv_threads) == 0);
1546: if (ret) {
1547: sock_shutdown(nbd);
1548: nbd_clear_que(nbd);
1549: }
1550:
1551: flush_workqueue(nbd->recv_workq);
1552: mutex_lock(&nbd->config_lock);
1553: nbd_bdev_reset(nbd);
1554: /* user requested, ignore socket errors */
1555: if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
1556: ret = 0;
1557: if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
1558: ret = -ETIMEDOUT;
1559: return ret;
1560: }
SourceFile:drivers/block/nbd.c]
|
| 58/2 |
2026/05/31 01:53 |
llm |
expert |
0m
Model:
Tokens:
input: 42061
output: 38
thoughts: 12
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:
**Diving into `nbd_start_device`**
Alright, so the task at hand involves examining `nbd_start_device`. That function name alone tells me we're likely dealing with the initialization or activation of an NBD (Network Block Device) within the kernel. My immediate mental checklist starts:
* **Device Structure:** I need to quickly refresh my understanding of the `nbd_device` struct. What fields are critical for the startup process? Things like the backing file descriptor, the connection state, any associated security parameters, and, of course, the access capabilities (read-only, write-enabled, etc.).
* **Resource Allocation/Check:** What resources does this function likely need to manage? Memory allocation for buffers, interrupt handling setup (if applicable), potential registration with the block layer. I'll be looking for things like mutexes or semaphores protecting critical sections. Are any limits, such as concurrent NBD devices, checked?
* **Error Handling:** It is very important to get a handle on the error handling within this function, especially within a kernel context. What are the potential failure scenarios? Is there proper cleanup of allocated resources? Are appropriate error codes being returned to the calling function? And also, can the kernel be brought down by this function?
* **Security Context:** Given that this involves network access and potentially remote data, the security aspects are always top of mind. Authentication, authorization, and perhaps even encryption if this is supported. Is there any obvious attack surface in the logic?
* **Concurrency:** Does `nbd_start_device` need to be thread-safe? Or is there any assumption of single-threaded operation? I'll be looking for synchronization primitives like mutexes or spinlocks protecting access to shared data structures. This is extremely important, as concurrency issues can lead to some tricky bugs.
Ultimately, I want to understand how this function transitions an NBD from an inactive to an active state, and where the potential bottlenecks or vulnerabilities might reside. Time to dig in and start tracing the code.
|
| 59/2 |
2026/05/31 01:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_start_device]
Results: map[SourceCode:1460: static int nbd_start_device(struct nbd_device *nbd)
1461: {
1462: struct nbd_config *config = nbd->config;
1463: int num_connections = config->num_connections;
1464: int error = 0, i;
1465:
1466: if (nbd->pid)
1467: return -EBUSY;
1468: if (!config->socks)
1469: return -EINVAL;
1470: if (num_connections > 1 &&
1471: !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1472: dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1473: return -EINVAL;
1474: }
1475:
1476: retry:
1477: mutex_unlock(&nbd->config_lock);
1478: blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1479: mutex_lock(&nbd->config_lock);
1480:
1481: /* if another code path updated nr_hw_queues, retry until succeed */
1482: if (num_connections != config->num_connections) {
1483: num_connections = config->num_connections;
1484: goto retry;
1485: }
1486:
1487: nbd->pid = task_pid_nr(current);
1488:
1489: nbd_parse_flags(nbd);
1490:
1491: error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1492: if (error) {
1493: dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1494: return error;
1495: }
1496: set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1497:
1498: nbd_dev_dbg_init(nbd);
1499: for (i = 0; i < num_connections; i++) {
1500: struct recv_thread_args *args;
1501:
1502: args = kzalloc(sizeof(*args), GFP_KERNEL);
1503: if (!args) {
1504: sock_shutdown(nbd);
1505: /*
1506: * If num_connections is m (2 < m),
1507: * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1508: * But NO.(n + 1) failed. We still have n recv threads.
1509: * So, add flush_workqueue here to prevent recv threads
1510: * dropping the last config_refs and trying to destroy
1511: * the workqueue from inside the workqueue.
1512: */
1513: if (i)
1514: flush_workqueue(nbd->recv_workq);
1515: return -ENOMEM;
1516: }
1517: sk_set_memalloc(config->socks[i]->sock->sk);
1518: if (nbd->tag_set.timeout)
1519: config->socks[i]->sock->sk->sk_sndtimeo =
1520: nbd->tag_set.timeout;
1521: atomic_inc(&config->recv_threads);
1522: refcount_inc(&nbd->config_refs);
1523: INIT_WORK(&args->work, recv_work);
1524: args->nbd = nbd;
1525: args->nsock = config->socks[i];
1526: args->index = i;
1527: queue_work(nbd->recv_workq, &args->work);
1528: }
1529: return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1530: }
SourceFile:drivers/block/nbd.c]
|
| 60/2 |
2026/05/31 01:54 |
llm |
expert |
1m
Model:
Tokens:
input: 43757
output: 39
thoughts: 1091
Thoughts: **Analyzing the NBD Driver's Block Size and Mount Behavior**
Okay, let's break this down. It seems we're looking at a potential race condition or misunderstanding in the Network Block Device (NBD) driver. The key line here is the block size initialization. `nbd_start_device` calls `nbd_set_size`, which, in turn, calculates the block size. It appears the `logical_block_size` gets set to 1024, derived from `NBD_DEF_BLKSIZE_BITS` and the bitshift operation.
So, `NBD_DO_IT` starts this process. But it blocks. The question is when does it do so? It appears the `nbd_set_size` is called BEFORE the device blocks. If `logical_block_size` really is 1024 as it should be, then `udf_fill_super` is later called and sets `uopt->blocksize` to 1024 too, and everything is aligned.
The real puzzle is why the warning is triggered.
Now, let's analyze the reproducer provided. It uses `ioctl` (NBD_DO_IT) followed by `mount`. Crucially, `NBD_DO_IT` is called on a different file descriptor (`fd_nbd2`) than the socket setup (`NBD_SET_SOCK` on `fd_nbd`). The core question becomes: how does the mount call succeed if `NBD_DO_IT` blocks? It seems that `NBD_DO_IT` *might* fail, and thus return immediately.
Let's trace the failure path within `NBD_DO_IT`. It calls `nbd_start_device_ioctl` which then calls `nbd_start_device`. In that function there are checks for errors: `EBUSY` and `EINVAL`. But `config->socks` is not NULL, so that path is ruled out.
Okay, let's go back to the idea that `nbd_start_device_ioctl` blocks with `wait_event_interruptible`. If the reproducer is single-threaded, how can it ever reach the `mount` call if the ioctl blocks? Then I remember that `wait_event_interruptible` *can* be interrupted by a signal! Syzkaller is notorious for sending signals to kill or interrupt threads, and therefore, an interrupt is likely. If interrupted, the function returns an error such as `-ERESTARTSYS`.
If it is interrupted, `sock_shutdown` and `nbd_clear_que` are called! Then `nbd_bdev_reset(nbd)`! This all seems to point to a scenario where a signal interrupts the `NBD_DO_IT` ioctl, causing a reset, which might explain the warning.
|
| 61/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_bdev_reset]
Results: map[SourceCode:1364: static void nbd_bdev_reset(struct nbd_device *nbd)
1365: {
1366: if (disk_openers(nbd->disk) > 1)
1367: return;
1368: set_capacity(nbd->disk, 0);
1369: }
SourceFile:drivers/block/nbd.c]
|
| 62/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 45632
output: 35
thoughts: 180
Thoughts: **Analyzing the Implications of nbd_bdev_reset**
Okay, so `nbd_bdev_reset` simply sets the capacity to zero. My initial thought is, does it also reset `logical_block_size`? No, it doesn't seem like it does. Now, let's consider a failure scenario. What if `NBD_DO_IT` fails *before* the `nbd_set_size` call? If it fails, the function returns immediately. The critical point is that if it fails early, `logical_block_size` isn't touched.
But hold on, let's explore a more intricate case. What if `NBD_DO_IT` isn't blocked? What if the condition `atomic_read(&config->recv_threads) == 0` is already true? I need to understand what happens in that context. Remember `nbd_start_device` queues `recv_work` on `nbd->recv_workq`. Then the `recv_work` thread runs `recv_work()`. I think I need to look closer at the execution path of the `recv_work` function to understand what is happening here.
|
| 63/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:recv_work]
Results: map[SourceCode: 967: static void recv_work(struct work_struct *work)
968: {
969: struct recv_thread_args *args = container_of(work,
970: struct recv_thread_args,
971: work);
972: struct nbd_device *nbd = args->nbd;
973: struct nbd_config *config = nbd->config;
974: struct request_queue *q = nbd->disk->queue;
975: struct nbd_sock *nsock = args->nsock;
976: struct nbd_cmd *cmd;
977: struct request *rq;
978:
979: while (1) {
980: struct nbd_reply reply;
981:
982: if (nbd_read_reply(nbd, nsock->sock, &reply))
983: break;
984:
985: /*
986: * Grab .q_usage_counter so request pool won't go away, then no
987: * request use-after-free is possible during nbd_handle_reply().
988: * If queue is frozen, there won't be any inflight requests, we
989: * needn't to handle the incoming garbage message.
990: */
991: if (!percpu_ref_tryget(&q->q_usage_counter)) {
992: dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
993: __func__);
994: break;
995: }
996:
997: cmd = nbd_handle_reply(nbd, args->index, &reply);
998: if (IS_ERR(cmd)) {
999: percpu_ref_put(&q->q_usage_counter);
1000: break;
1001: }
1002:
1003: rq = blk_mq_rq_from_pdu(cmd);
1004: if (likely(!blk_should_fake_timeout(rq->q))) {
1005: bool complete;
1006:
1007: mutex_lock(&cmd->lock);
1008: complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1009: &cmd->flags);
1010: mutex_unlock(&cmd->lock);
1011: if (complete)
1012: blk_mq_complete_request(rq);
1013: }
1014: percpu_ref_put(&q->q_usage_counter);
1015: }
1016:
1017: mutex_lock(&nsock->tx_lock);
1018: nbd_mark_nsock_dead(nbd, nsock, 1);
1019: mutex_unlock(&nsock->tx_lock);
1020:
1021: nbd_config_put(nbd);
1022: atomic_dec(&config->recv_threads);
1023: wake_up(&config->recv_wq);
1024: kfree(args);
1025: }
SourceFile:drivers/block/nbd.c]
|
| 64/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 47036
output: 38
thoughts: 1678
Thoughts: **Analyzing the UDF Mount Issue**
Okay, let's break this down. `recv_work` kicks off and calls `nbd_read_reply`. If that fails – which it *will* with the reproducer's setup of a new, unconnected socket – then the loop breaks. `recv_work` exits quickly, after decrementing the receive thread count and waking up the work queue. The socket is new and unconnected, so the `nbd_read_reply` fails immediately. `nbd_start_device_ioctl` gets to run and returns fast, which makes `NBD_DO_IT` return quickly too. That sets `logical_block_size` to 1024.
Now, if `logical_block_size` is 1024, `udf_fill_super` sets `uopt->blocksize = 1024` and then `sb_set_blocksize(sb, 1024)` is called. That means `IS_ALIGNED(1024, 1024)` is true, so the warning shouldn't trigger.
The key here is that the reproducer *doesn't* call `NBD_SET_BLKSIZE`. So mount options are all default. Looking at the reproducer code, the `data` pointer is NULL, so no specific options are passed to the mount call. `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)` is definitely false. So, `uopt->blocksize` will be initialized to `bdev_logical_block_size(sb->s_bdev)`. But why does it start to read blocks with a different value?
Let's assume `bdev_logical_block_size` is 512. If `NBD_DO_IT` was never called, then `logical_block_size` would be 512. But because `NBD_DO_IT` runs, `logical_block_size` is set to 1024. The reproducer is single-threaded, so `NBD_DO_IT` returns before mount is called. So, the `logical_block_size` is 1024 when the mount occurs.
If `udf_load_vrs` fails to load correctly, then `udf_fill_super` will double the blocksize via `uopt->blocksize <<= 1;`. Then `udf_load_vrs(sb, uopt, silent, &fileset)` is called again. Crucially, that calls `sb_set_blocksize(sb, uopt->blocksize)`. If that fails, then `sb->s_blocksize` will become 2048. So, now `IS_ALIGNED(2048, 1024)` will still be true. It's the same pattern if `uopt->blocksize` becomes 4096.
The loop condition in `udf_fill_super` is `while (uopt->blocksize <= 4096)`, so it will stop there. The block size is always a multiple of 1024. I don't understand why `IS_ALIGNED(size, bdev_logical_block_size(bdev))` would be false in this situation.
If `NBD_DO_IT` failed *before* `nbd_set_size` was called, then `logical_block_size` starts at 512. In this case, `uopt->blocksize` will be initialized to 512 and then it will double up to 1024, 2048 and 4096. All of these values are multiples of 512, so the alignment should still be correct!
Wait! Could the value of `bdev_logical_block_size(bdev)` change during `udf_load_vrs`? But again, the reproducer is single-threaded. There's no concurrent `ioctl` call that would change the block size. Maybe there's some background task at play? Let's investigate `nbd_clear_que`.
|
| 65/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_clear_que]
Results: map[SourceCode:1047: static void nbd_clear_que(struct nbd_device *nbd)
1048: {
1049: blk_mq_quiesce_queue(nbd->disk->queue);
1050: blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
1051: blk_mq_unquiesce_queue(nbd->disk->queue);
1052: dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
1053: }
SourceFile:drivers/block/nbd.c]
|
| 66/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 49854
output: 39
thoughts: 12
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to an expert:
**Investigating NBD Block Device Reset Behavior**
Alright, so I'm looking at this whole block device situation, specifically with the Network Block Device. My immediate thought zeroes in on `nbd_bdev_reset`. This function... it's the lynchpin, isn't it? It's where the magic happens, or *should* happen, when you need to bring a block device back to a known state. But I'm pondering the nuances. What does a "reset" *really* mean in the context of NBD? Are we talking about clearing the cache, invalidating stale data, re-establishing connections, or something more fundamental? I need to delve into the implementation details of this function. I'm wondering if there are edge cases, race conditions, or subtle behaviors that I need to be aware of and should test. I need to figure out when to call this function, under what conditions it needs to be called, what the expected behavior is in those situations, and how it handles failures. So, `nbd_bdev_reset`... that's where I need to start digging.
|
| 67/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_bdev_reset]
Results: map[SourceCode:1364: static void nbd_bdev_reset(struct nbd_device *nbd)
1365: {
1366: if (disk_openers(nbd->disk) > 1)
1367: return;
1368: set_capacity(nbd->disk, 0);
1369: }
SourceFile:drivers/block/nbd.c]
|
| 68/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 50290
output: 38
thoughts: 60
Thoughts: Here's my summary, as though I'm thinking through this process:
**A Quick Puzzle with NBD Device Capacity**
Okay, let's see, I'm tracing through this NBD device initialization, and it's hitting me right here: `nbd_start_device_ioctl` is calling `nbd_bdev_reset(nbd)`. The tricky part is, what exactly *does* `nbd_bdev_reset` do? Oh, right, it just sets the device capacity to zero. That seems... potentially problematic.
Now I'm thinking about the implications. What happens if, down the line, `nbd_config_put` is called? Does this capacity reset set up a problematic situation by interfering with other initialization stages? I need to look into whether this zeroing of the capacity interacts with configuration teardown in unexpected ways. It feels like I'm missing some crucial piece of the puzzle here, and it's probably related to how the device capacity is handled throughout the entire lifecycle. This smells like a possible race condition, or at least a situation ripe for misuse if the code isn't very carefully sequenced.
|
| 69/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_config_put]
Results: map[SourceCode:1421: static void nbd_config_put(struct nbd_device *nbd)
1422: {
1423: if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1424: &nbd->config_lock)) {
1425: struct nbd_config *config = nbd->config;
1426: nbd_dev_dbg_close(nbd);
1427: invalidate_disk(nbd->disk);
1428: if (nbd->config->bytesize)
1429: kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1430: if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1431: &config->runtime_flags))
1432: device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1433: nbd->pid = 0;
1434: if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1435: &config->runtime_flags)) {
1436: device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1437: kfree(nbd->backend);
1438: nbd->backend = NULL;
1439: }
1440: nbd_clear_sock(nbd);
1441: if (config->num_connections) {
1442: int i;
1443: for (i = 0; i < config->num_connections; i++) {
1444: sockfd_put(config->socks[i]->sock);
1445: kfree(config->socks[i]);
1446: }
1447: kfree(config->socks);
1448: }
1449: kfree(nbd->config);
1450: nbd->config = NULL;
1451:
1452: nbd->tag_set.timeout = 0;
1453:
1454: mutex_unlock(&nbd->config_lock);
1455: nbd_put(nbd);
1456: module_put(THIS_MODULE);
1457: }
1458: }
SourceFile:drivers/block/nbd.c]
|
| 70/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 51301
output: 36
thoughts: 136
Thoughts: **Analyzing the Potential for Configuration Reset in NBD**
Okay, so I'm digging into this `nbd_config_put` function. It looks like it frees up the `nbd->config` pointer and sets it to NULL. That's good housekeeping, but I need to be sure about the implications for my `logical_block_size`. Does this function implicitly reset it, or is it handled elsewhere? Hmm, it doesn't appear to call `nbd_set_size` or `queue_limits_commit_update`, so the `logical_block_size` should remain at 1024. That makes sense.
But wait, what happens if `nbd_alloc_and_init_config` gets called AGAIN? Is that a possibility after a disconnect and remount, for instance? If a `mount` operation opens the block device again, does it call that initialization function? I need to be absolutely certain of this, especially if there are subsequent operations based on the assumption of this configuration being established. I should check the `nbd_open` function, which is the gateway to get a handle, and see if there are any calls to that allocator in there. That's the key to understanding the full lifecycle of the config structure and its parameters.
|
| 71/2 |
2026/05/31 01:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_open]
Results: map[SourceCode:1694: static int nbd_open(struct gendisk *disk, blk_mode_t mode)
1695: {
1696: struct nbd_device *nbd;
1697: struct nbd_config *config;
1698: int ret = 0;
1699:
1700: mutex_lock(&nbd_index_mutex);
1701: nbd = disk->private_data;
1702: if (!nbd) {
1703: ret = -ENXIO;
1704: goto out;
1705: }
1706: if (!refcount_inc_not_zero(&nbd->refs)) {
1707: ret = -ENXIO;
1708: goto out;
1709: }
1710:
1711: config = nbd_get_config_unlocked(nbd);
1712: if (!config) {
1713: mutex_lock(&nbd->config_lock);
1714: if (refcount_inc_not_zero(&nbd->config_refs)) {
1715: mutex_unlock(&nbd->config_lock);
1716: goto out;
1717: }
1718: ret = nbd_alloc_and_init_config(nbd);
1719: if (ret) {
1720: mutex_unlock(&nbd->config_lock);
1721: goto out;
1722: }
1723:
1724: refcount_inc(&nbd->refs);
1725: mutex_unlock(&nbd->config_lock);
1726: if (max_part)
1727: set_bit(GD_NEED_PART_SCAN, &disk->state);
1728: } else if (nbd_disconnected(config)) {
1729: if (max_part)
1730: set_bit(GD_NEED_PART_SCAN, &disk->state);
1731: }
1732: out:
1733: mutex_unlock(&nbd_index_mutex);
1734: return ret;
1735: }
SourceFile:drivers/block/nbd.c]
|
| 72/2 |
2026/05/31 01:55 |
llm |
expert |
0m
Model:
Tokens:
input: 52377
output: 38
thoughts: 2928
Thoughts: **Analyzing the NBD and UDF Interaction**
Okay, so I'm diving into this warning in the buffer.c code, trying to figure out how the block size alignment is getting tripped up. First, I see that `nbd_open` can set up a default block size of 1024 through `nbd_alloc_and_init_config`, which is stored in `config->blksize_bits`. But it doesn't immediately call `nbd_set_size`, which is odd. This leaves the `logical_block_size` potentially uninitialized.
Then, the UDF filesystem code, specifically `udf_fill_super`, comes into play. It initializes `uopt->blocksize` with the device's logical block size, and sets the superblock block size via `sb_set_blocksize`. The crucial part is how `udf_load_vrs` gets involved with `sb_bread`. The warning seems to stem from a misalignment check: `IS_ALIGNED(size, bdev_logical_block_size(bdev))`. `bdev_logical_block_size(bdev)` is being checked against the `sb->s_blocksize` that UDF will set.
Initially, I thought that this was an issue with `bdev_logical_block_size(bdev)` changing after being set, so that `sb->s_blocksize` would be smaller. But, `sb->s_blocksize` gets its initial value and then can be increased, but not decreased. My assumption that bdev might be larger proved false, because `nbd_set_size` sets the device size when the ioctl is called. I had to consider cases where the bdev's logical block size might be smaller.
However, after looking at the syzkaller reproducer, it turns out that I wasn't accounting for the concurrency between the NBD ioctls. `NBD_DO_IT` starts `recv_work`, which runs asynchronously on a workqueue, and calls `nbd_read_reply`. Crucially, this happens after `nbd_open` has set the initial logical block size to 1024, if the config struct is null.
But, the syzkaller repro uses separate file descriptors for `NBD_SET_SOCK` and `NBD_DO_IT`, so the setting of the NBD size, done in `nbd_start_device`, can run asynchronously. This occurs after a `socket` has been created, but not connected. The `nbd_read_reply` then immediately fails with `-ENOTCONN`, which wakes up `NBD_DO_IT`, causing it to complete immediately.
The mount call will then proceed and `uopt->blocksize` will be set, but if `udf_load_vrs` proceeds and reads a block, this triggers the warning because `bdev_logical_block_size` might be changed. I realized it is because the initial socket returns an immediate error!
The final piece: the `size` argument to the warning comes from `sb->s_blocksize`, which is set by the UDF code. So, in order to trigger the warning, it must be the case that `sb->s_blocksize` from the UDF side is *larger* than `bdev_logical_block_size`.
But, wait. How can `sb->s_blocksize` become larger? The logical block size is set, and never changes, unless this is a *single threaded* reproducer, which should not be possible due to the asynchronous worker.
|
| 73/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/misc.c Name:udf_read_tagged]
Results: map[SourceCode: 178: /*
179: * udf_read_tagged
180: *
181: * PURPOSE
182: * Read the first block of a tagged descriptor.
183: *
184: * HISTORY
185: * July 1, 1997 - Andrew E. Mileski
186: * Written, tested, and released.
187: */
188: struct buffer_head *udf_read_tagged(struct super_block *sb, uint32_t block,
189: uint32_t location, uint16_t *ident)
190: {
191: struct tag *tag_p;
192: struct buffer_head *bh = NULL;
193: u8 checksum;
194:
195: /* Read the block */
196: if (block == 0xFFFFFFFF)
197: return NULL;
198:
199: bh = sb_bread(sb, block);
200: if (!bh) {
201: udf_err(sb, "read failed, block=%u, location=%u\n",
202: block, location);
203: return NULL;
204: }
205:
206: tag_p = (struct tag *)(bh->b_data);
207:
208: *ident = le16_to_cpu(tag_p->tagIdent);
209:
210: if (location != le32_to_cpu(tag_p->tagLocation)) {
211: udf_debug("location mismatch block %u, tag %u != %u\n",
212: block, le32_to_cpu(tag_p->tagLocation), location);
213: goto error_out;
214: }
215:
216: /* Verify the tag checksum */
217: checksum = udf_tag_checksum(tag_p);
218: if (checksum != tag_p->tagChecksum) {
219: udf_err(sb, "tag checksum failed, block %u: 0x%02x != 0x%02x\n",
220: block, checksum, tag_p->tagChecksum);
221: goto error_out;
222: }
223:
224: /* Verify the tag version */
225: if (tag_p->descVersion != cpu_to_le16(0x0002U) &&
226: tag_p->descVersion != cpu_to_le16(0x0003U)) {
227: udf_err(sb, "tag version 0x%04x != 0x0002 || 0x0003, block %u\n",
228: le16_to_cpu(tag_p->descVersion), block);
229: goto error_out;
230: }
231:
232: /* Verify the descriptor CRC */
233: if (le16_to_cpu(tag_p->descCRCLength) + sizeof(struct tag) > sb->s_blocksize ||
234: le16_to_cpu(tag_p->descCRC) == crc_itu_t(0,
235: bh->b_data + sizeof(struct tag),
236: le16_to_cpu(tag_p->descCRCLength)))
237: return bh;
238:
239: udf_debug("Crc failure block %u: crc = %u, crclen = %u\n", block,
240: le16_to_cpu(tag_p->descCRC),
241: le16_to_cpu(tag_p->descCRCLength));
242: error_out:
243: brelse(bh);
244: return NULL;
245: }
SourceFile:fs/udf/misc.c]
|
| 74/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 57270
output: 36
thoughts: 41
Thoughts: Okay, here's my interpretation of those thoughts, framed as my own:
**Analyzing `udf_read_tagged` and its Dependence on `sb_bread`**
Right, let me see... I'm looking at `udf_read_tagged`, and it's calling `sb_bread` within its execution path. Ah, yes, `sb_bread`... that's the inline function defined in `include/linux/buffer_head.h`. So, it's a fundamental part of how `udf_read_tagged` reads data from the storage buffer. Interesting. I need to keep that in mind when I think about how it handles block reads. The performance implication of an inline function is that, in theory, there's no function call overhead. That's good from a speed perspective, assuming the code is simple enough for the compiler to effectively inline it. I should probably dive into `sb_bread` itself later to see exactly what it's doing with the buffer head, especially when thinking about the UDF filesystem and potential optimizations for block reading.
|
| 75/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/buffer_head.h Name:sb_bread]
Results: map[SourceCode: 343: static inline struct buffer_head *
344: sb_bread(struct super_block *sb, sector_t block)
345: {
346: return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
347: }
SourceFile:include/linux/buffer_head.h]
|
| 76/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 57698
output: 40
thoughts: 1216
Thoughts: **Analyzing the Block Size Mismatch in UDF Filesystem Mounting**
Okay, so I'm looking at this warning that's being triggered, and it seems to be related to a discrepancy between the filesystem's block size (`sb->s_blocksize`) and the underlying device's logical block size (`bdev_logical_block_size(bdev)`). The core issue is this: if the block size (`size`) is exactly the same as the superblock's block size (`sb->s_blocksize`), then the alignment check (`IS_ALIGNED(sb->s_blocksize, bdev_logical_block_size(bdev))`) should logically be TRUE. But it's not. That's a red flag!
My initial thought was, "Could `bdev_logical_block_size(bdev)` somehow be *larger* than `sb->s_blocksize`?" That seems counterintuitive, but if it were true, then with `sb->s_blocksize` being, say, 512, and `bdev_logical_block_size(bdev)` being 1024, the alignment check would indeed fail (as `IS_ALIGNED(512, 1024)` is `!(512 & 1023)` which is `!(512)` or FALSE). That would explain the warning!
Now, the `udf_fill_super` function comes into play. It appears to be initializing the superblock:
```c
uopt->blocksize = bdev_logical_block_size(sb->s_bdev);
while (uopt->blocksize <= 4096) {
ret = udf_load_vrs(sb, uopt, silent, &fileset);
```
If `bdev_logical_block_size(sb->s_bdev)` is initially 1024, `uopt->blocksize` gets initialized to 1024, `sb_set_blocksize(sb, 1024)` is called, and everything is aligned. So the problem must not be triggered with those initial values!
However, what if `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)` is true? The reproducer does NOT seem to pass `bs=512`, so there's not a `blocksize` option that is interfering.
AHA! Could `bdev_logical_block_size(sb->s_bdev)` CHANGE *after* `uopt->blocksize` is initialized? That sounds like a race condition, and it's looking promising! If the device's logical block size starts at 512, `uopt->blocksize` gets set to 512, `sb_set_blocksize(sb, 512)` is called, and `sb->s_blocksize` *becomes* 512. Now, CONCURRENTLY (or nearly so), if `bdev_logical_block_size(sb->s_bdev)` changes to 1024 *after* that initialization, then the subsequent `sb_bread` call within `udf_load_vrs` will call `__bread_gfp` with a `size=512`. That triggers the misalignment warning inside `__getblk_slow` because `IS_ALIGNED(512, 1024)` is FALSE! That seems like a plausible explanation: a race condition where the device's block size changes *during* the filesystem mounting process.
But wait a minute... the reproducer is single-threaded, isn't it? So how could this change concurrently? I need to look closely at what's going on. Tracing the reproducers shows the following:
```c
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xab00, /*arg=*/r[1]); // NBD_SET_SOCK
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0); // NBD_DO_IT
syscall(__NR_mount, /*src=*/0x200000000000ul, /*dst=*/0x200000004a00ul, /*type=*/0x200000000080ul, /*flags=MS_LAZYTIME|MS_SILENT|MS_RDONLY|MS_NOSUID|MS_NODEV|0x80*/0x2008087ul, /*
|
| 77/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_start_device_ioctl]
Results: map[SourceCode:1532: static int nbd_start_device_ioctl(struct nbd_device *nbd)
1533: {
1534: struct nbd_config *config = nbd->config;
1535: int ret;
1536:
1537: ret = nbd_start_device(nbd);
1538: if (ret)
1539: return ret;
1540:
1541: if (max_part)
1542: set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
1543: mutex_unlock(&nbd->config_lock);
1544: ret = wait_event_interruptible(config->recv_wq,
1545: atomic_read(&config->recv_threads) == 0);
1546: if (ret) {
1547: sock_shutdown(nbd);
1548: nbd_clear_que(nbd);
1549: }
1550:
1551: flush_workqueue(nbd->recv_workq);
1552: mutex_lock(&nbd->config_lock);
1553: nbd_bdev_reset(nbd);
1554: /* user requested, ignore socket errors */
1555: if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
1556: ret = 0;
1557: if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
1558: ret = -ETIMEDOUT;
1559: return ret;
1560: }
SourceFile:drivers/block/nbd.c]
|
| 78/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 60464
output: 35
thoughts: 167
Thoughts: **Investigating a Potential Capacity Reset Issue in the NBD Driver**
Okay, so I'm digging into this NBD driver code, and I see that `nbd_start_device_ioctl` calls `nbd_bdev_reset(nbd)`. Fair enough. Let's see what *that* does. Ah, `nbd_bdev_reset` calls `set_capacity(nbd->disk, 0)`. Makes sense, we're zeroing out the capacity on device initialization. However, it seems that the code doesn't reset `logical_block_size`.
But wait a minute… what happens if `nbd_config_put` gets called? My concern now is about how that interacts with this capacity reset. Okay, let's refresh my memory on `nbd_config_put`. Ah, yes, it frees `nbd->config` and sets the pointer to NULL. When does *that* happen? I need to track down the call sites.
Okay, I'm going through the code. It seems like `recv_work` calls `nbd_config_put(nbd)` at the end of the processing! Alright, alright. This is crucial because it's a critical path! Let me double check that `recv_work` calls `nbd_config_put(nbd)`! Yes, `recv_work` indeed calls `nbd_config_put(nbd)`! I need to re-examine that `recv_work` function more closely now.
|
| 79/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:recv_work]
Results: map[SourceCode: 967: static void recv_work(struct work_struct *work)
968: {
969: struct recv_thread_args *args = container_of(work,
970: struct recv_thread_args,
971: work);
972: struct nbd_device *nbd = args->nbd;
973: struct nbd_config *config = nbd->config;
974: struct request_queue *q = nbd->disk->queue;
975: struct nbd_sock *nsock = args->nsock;
976: struct nbd_cmd *cmd;
977: struct request *rq;
978:
979: while (1) {
980: struct nbd_reply reply;
981:
982: if (nbd_read_reply(nbd, nsock->sock, &reply))
983: break;
984:
985: /*
986: * Grab .q_usage_counter so request pool won't go away, then no
987: * request use-after-free is possible during nbd_handle_reply().
988: * If queue is frozen, there won't be any inflight requests, we
989: * needn't to handle the incoming garbage message.
990: */
991: if (!percpu_ref_tryget(&q->q_usage_counter)) {
992: dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
993: __func__);
994: break;
995: }
996:
997: cmd = nbd_handle_reply(nbd, args->index, &reply);
998: if (IS_ERR(cmd)) {
999: percpu_ref_put(&q->q_usage_counter);
1000: break;
1001: }
1002:
1003: rq = blk_mq_rq_from_pdu(cmd);
1004: if (likely(!blk_should_fake_timeout(rq->q))) {
1005: bool complete;
1006:
1007: mutex_lock(&cmd->lock);
1008: complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1009: &cmd->flags);
1010: mutex_unlock(&cmd->lock);
1011: if (complete)
1012: blk_mq_complete_request(rq);
1013: }
1014: percpu_ref_put(&q->q_usage_counter);
1015: }
1016:
1017: mutex_lock(&nsock->tx_lock);
1018: nbd_mark_nsock_dead(nbd, nsock, 1);
1019: mutex_unlock(&nsock->tx_lock);
1020:
1021: nbd_config_put(nbd);
1022: atomic_dec(&config->recv_threads);
1023: wake_up(&config->recv_wq);
1024: kfree(args);
1025: }
SourceFile:drivers/block/nbd.c]
|
| 80/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 61928
output: 36
thoughts: 157
Thoughts: **Analyzing the Reference Counting in the NBD Driver**
Okay, so I'm tracing the lifecycle of the `nbd->config` structure. I see that `recv_work` calls `nbd_config_put(nbd)`. Right, that function is responsible for decrementing `nbd->config_refs`. The critical part is what happens when that reference count hits zero. At that point, `nbd_config_put` frees `nbd->config` and sets the pointer to NULL, effectively cleaning up the configuration data.
But hold on, now I need to factor in where these references are added. If `nbd_start_device` increments `nbd->config_refs` on every `recv_work` *invocation* then this is a race condition. But it seems likely it only increments it once during the start up of the device. Also, is it *just* `recv_work` that's involved, or are there other parts of the code that also hold a reference?
I thought maybe `nbd_ioctl` might hold a reference too, but let me check...No, `nbd_ioctl` doesn't seem to be involved in reference counting the configuration. That's good.
Wait a minute, what about `nbd_open`? *That* seems like a likely suspect to hold a reference to `nbd->config`. I'll have to investigate that function to confirm whether it participates in the reference counting scheme.
|
| 81/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_open]
Results: map[SourceCode:1694: static int nbd_open(struct gendisk *disk, blk_mode_t mode)
1695: {
1696: struct nbd_device *nbd;
1697: struct nbd_config *config;
1698: int ret = 0;
1699:
1700: mutex_lock(&nbd_index_mutex);
1701: nbd = disk->private_data;
1702: if (!nbd) {
1703: ret = -ENXIO;
1704: goto out;
1705: }
1706: if (!refcount_inc_not_zero(&nbd->refs)) {
1707: ret = -ENXIO;
1708: goto out;
1709: }
1710:
1711: config = nbd_get_config_unlocked(nbd);
1712: if (!config) {
1713: mutex_lock(&nbd->config_lock);
1714: if (refcount_inc_not_zero(&nbd->config_refs)) {
1715: mutex_unlock(&nbd->config_lock);
1716: goto out;
1717: }
1718: ret = nbd_alloc_and_init_config(nbd);
1719: if (ret) {
1720: mutex_unlock(&nbd->config_lock);
1721: goto out;
1722: }
1723:
1724: refcount_inc(&nbd->refs);
1725: mutex_unlock(&nbd->config_lock);
1726: if (max_part)
1727: set_bit(GD_NEED_PART_SCAN, &disk->state);
1728: } else if (nbd_disconnected(config)) {
1729: if (max_part)
1730: set_bit(GD_NEED_PART_SCAN, &disk->state);
1731: }
1732: out:
1733: mutex_unlock(&nbd_index_mutex);
1734: return ret;
1735: }
SourceFile:drivers/block/nbd.c]
|
| 82/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 63069
output: 36
thoughts: 84
Thoughts: Here's my analysis of the `nbd_open` function and the associated reference counting:
**`nbd_open` and Configuration Reference Counting**
Okay, so `nbd_open` clearly increments `nbd->refs`, that's straightforward enough – tracking how many users are utilizing this NBD device. Now, the interesting bit. If the configuration pointer `config` is `NULL`, the function helpfully calls `nbd_alloc_and_init_config`. Fine. But, hang on... that `nbd_alloc_and_init_config` function then sets `nbd->config_refs` to 1. That *immediately* raises a question in my mind: If `nbd_open` is the one setting `nbd->config_refs` to 1 initially, then who, precisely, is responsible for decrementing this reference counter? I can see the potential for a very nasty memory leak if this isn't handled correctly. Aha! *nbd_release* – that's the likely candidate, the release function. I'll need to check the logic there to confirm my suspicion and ensure proper deallocation, but I bet that's where the config reference will get decremented.
|
| 83/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_release]
Results: map[SourceCode:1737: static void nbd_release(struct gendisk *disk)
1738: {
1739: struct nbd_device *nbd = disk->private_data;
1740:
1741: if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
1742: disk_openers(disk) == 0)
1743: nbd_disconnect_and_put(nbd);
1744:
1745: nbd_config_put(nbd);
1746: nbd_put(nbd);
1747: }
SourceFile:drivers/block/nbd.c]
|
| 84/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 63658
output: 33
thoughts: 1199
Thoughts: **Deconstructing the NBD Block Size Puzzle**
Okay, let's break this down. It seems we're dealing with a block size discrepancy in the NBD driver, and it's causing a warning we need to understand. First, `nbd_release` calls `nbd_config_put`. This is the core of the problem, right? `nbd_open` takes a reference on `nbd->config_refs`, and `nbd_release` drops it. But, and here's the kicker, `nbd_start_device` *also* increments `nbd->config_refs` for each `recv_work`. `recv_work` subsequently drops its reference upon exiting. The key here is that if `recv_work` exits, the reference from `nbd_open` is still held, meaning `nbd->config` is not freed. Therefore, `logical_block_size` *remains* at 1024!
Now, if `logical_block_size` stays at 1024, the `mount` call subsequently finds a non-NULL `config` due to the persistent reference held by `nbd_open`, thus just returns early. Then, `udf_fill_super` sets `uopt->blocksize = 1024`, and `sb_set_blocksize(sb, 1024)` is called, so `IS_ALIGNED(1024, 1024)` is TRUE. So, why are we seeing a warning?
Let's look at the reproducer: it calls `NBD_DO_IT` *before* `mount`. It's calling `syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xab03, 0)`, which is `NBD_DO_IT` on `r[2]`. `r[2]` was opened with `O_RDONLY` (because `flags=0` in `syz_open_dev`), thus `nbd_open` allocates `config` and sets `config->blksize_bits = 10`. Critically, it *doesn't* call `nbd_set_size` initially, so `logical_block_size` is still 512 at this point! Then, `NBD_DO_IT` calls `nbd_start_device` which *does* call `nbd_set_size(nbd, config->bytesize, 1024)`. This sets `logical_block_size` to 1024. `NBD_DO_IT` blocks. `recv_work` fails, so `NBD_DO_IT` returns. Now, `mount` is called, and, `logical_block_size` is 1024. So `uopt->blocksize` is 1024, `sb_set_blocksize(sb, 1024)` happens, and `IS_ALIGNED(1024, 1024)` is true.
Now, if `NBD_DO_IT` isn't called, then `logical_block_size` stays at 512, which is fine, because `IS_ALIGNED(512, 512)` will also be true.
But what about concurrency? The reproducer is single-threaded, so that's not it. Is there any background work resetting `logical_block_size` to 512? We checked `nbd_release`, that doesn't seem to be it. When `NBD_DO_IT` returns, does it close `r[2]`? No, it doesn't. And `r[0]` and `r[2]` are both open. When `mount` calls, it opens `/dev/nbd0` again and calls `udf_fill_super`. `NBD_CLEAR_SOCK` is not called, so that is not the issue. `nbd_bdev_reset` doesn't reset it, nor does `set_capacity`. Okay, let's now look closer at that `set_capacity` call. I need to understand that.
|
| 85/2 |
2026/05/31 01:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/genhd.c Name:set_capacity]
Results: map[SourceCode: 59: void set_capacity(struct gendisk *disk, sector_t sectors)
60: {
61: if (sectors > BLK_DEV_MAX_SECTORS) {
62: pr_warn_once("%s: truncate capacity from %lld to %lld\n",
63: disk->disk_name, sectors,
64: BLK_DEV_MAX_SECTORS);
65: sectors = BLK_DEV_MAX_SECTORS;
66: }
67:
68: bdev_set_nr_sectors(disk->part0, sectors);
69: }
SourceFile:block/genhd.c]
|
| 86/2 |
2026/05/31 01:56 |
llm |
expert |
0m
Model:
Tokens:
input: 66012
output: 40
thoughts: 956
Thoughts: **Analyzing the UDF Filesystem Alignment Warning**
Okay, first thought: is there a scenario where the reported condition *isn't* true? No, that's not it. Then, what if `nbd_set_size` is called with `blksize=0`? That would be interesting, but `nbd_set_size` sets `blksize = 1u << NBD_DEF_BLKSIZE_BITS` (which is 1024), so that's a dead end. Okay, what if `nbd_set_size` is called with `blksize=512`? The reproducer *doesn't* call `NBD_SET_BLKSIZE`. Let's look at the reproducer carefully.
Alright, the reproducer calls `mount` on `/dev/nbd0`. `r[0]` and `r[2]` are opened with `/dev/nbd#`, which the `syz_open_dev` function converts to `/dev/nbd0` if the id is 0, which it is. I'm wondering if `NBD_DO_IT` blocks. If `NBD_DO_IT` blocks, and `mount` is NEVER reached, how can the warning trigger? It triggers in `udf_fill_super`, which is *called by* `mount`, so `mount` *must* be reached. But how if `NBD_DO_IT` blocks? Ah, but it *returns*! Why? Because `recv_work` fails and wakes it up. So `nbd_start_device_ioctl` returns if `recv_work` fails, and then `mount` is called. So then `logical_block_size` is 1024. Then `sb_set_blocksize(sb, 1024)` is called and so `IS_ALIGNED(1024, 1024)` is true! Why does the warning trigger?
Wait, what if `udf_load_vrs` FAILS, and `uopt->blocksize` is doubled to 2048? Then `sb_set_blocksize(sb, 2048)` is called. And `IS_ALIGNED(2048, 1024)` *is* true! How about if it doubles to 4096? Still true! Maybe I should check `udf_load_vrs` calls `udf_check_anchor_block`, and then I should check `udf_check_anchor_block`. Let's go there next.
|
| 87/2 |
2026/05/31 01:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:udf_check_anchor_block]
Results: map[SourceCode:1898: /*
1899: * Check whether there is an anchor block in the given block and
1900: * load Volume Descriptor Sequence if so.
1901: *
1902: * Returns <0 on error, 0 on success, -EAGAIN is special - try next anchor
1903: * block
1904: */
1905: static int udf_check_anchor_block(struct super_block *sb, sector_t block,
1906: struct kernel_lb_addr *fileset)
1907: {
1908: struct buffer_head *bh;
1909: uint16_t ident;
1910: int ret;
1911:
1912: bh = udf_read_tagged(sb, block, block, &ident);
1913: if (!bh)
1914: return -EAGAIN;
1915: if (ident != TAG_IDENT_AVDP) {
1916: brelse(bh);
1917: return -EAGAIN;
1918: }
1919: ret = udf_load_sequence(sb, bh, fileset);
1920: brelse(bh);
1921: return ret;
1922: }
SourceFile:fs/udf/super.c]
|
| 88/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 67958
output: 44
thoughts: 740
Thoughts: **Analyzing a Potential Alignment Issue in UDF Filesystem Code**
Okay, let's break this down. `udf_check_anchor_block` is calling `udf_read_tagged`, which in turn calls `sb_bread`. This chain of function calls ultimately leads to a call to `__bread_gfp`. The critical point here is that `sb_bread` is using `sb->s_blocksize` as the `size` argument. Now, if the file system's block size (`sb->s_blocksize`) is a multiple of the underlying block device's logical block size (`bdev_logical_block_size(bdev)`), then the check `IS_ALIGNED(size, bdev_logical_block_size(bdev))` *should* always evaluate to true. But I have to be absolutely certain...
The question then becomes, is there *any* scenario where `sb->s_blocksize` wouldn't be a multiple of `bdev_logical_block_size(bdev)`? The key seems to be if the latter is somehow larger, which seemed impossible. Initially, I considered a scenario where `bdev_logical_block_size(bdev)` is larger than `sb->s_blocksize`, say, 4096 vs. 1024, respectively. However, `udf_fill_super` sets `uopt->blocksize` to `bdev_logical_block_size(sb->s_bdev)`, then `sb_set_blocksize(sb, 4096)` is called. This initialization seems to ensure that they are the same value. So the block size in the super block is synchronized.
But then, a disturbing thought – what if `bdev_logical_block_size(bdev)` *changes* after `sb_set_blocksize`? Let's say it's initially 512, then it changes to 1024. Now, the `sb_bread` call might pass `size=512`. `IS_ALIGNED(512, 1024)` would, of course, be false! This is a serious concern. The challenge is figuring out how `bdev_logical_block_size(bdev)` could change *after* the superblock is initialized.
Could this be a concurrency issue? Perhaps if `NBD_DO_IT` is called concurrently with the mount. But the reproducer is single-threaded, so this is unlikely. So, I have to consider other cases where the size may change.
Could `recv_work` or some other NBD component be changing the size? It doesn't appear so at first glance. `recv_work` doesn't directly change the logical block size. But could there be a call to something like `nbd_set_size` or `nbd_size_update`? I need to check the codebase to see if `nbd_set_size` is called elsewhere. That's the likely culprit, I would imagine. Let me review the code.
|
| 89/2 |
2026/05/31 01:57 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:drivers/block/nbd.c IncludeSnippetLines:0 Name:nbd_set_size]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1597] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1599] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1603] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_genl_size_set SourceFile:drivers/block/nbd.c SourceLine:2058] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1529]] TruncatedOutput:false]
|
| 90/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 69688
output: 37
thoughts: 131
Thoughts: **Analyzing the Size Setting Mechanism in the NBD Driver**
Okay, so I'm digging into how the block size and size are set within the Network Block Device (NBD) driver. It looks like `nbd_set_size` is a central function here. My initial thought is to trace where it's called from, to understand the different ways a device's characteristics can be modified. I see it's called from `__nbd_ioctl`, specifically for `NBD_SET_BLKSIZE`, `NBD_SET_SIZE`, and `NBD_CLEAR_SOCK`. That makes sense; those ioctls would naturally involve changes to the device size or block parameters. Additionally, it gets called via `nbd_genl_size_set` using netlink, which is the modern interface. Finally, I see it's called by `nbd_start_device`, which is triggered by `NBD_DO_IT` or netlink.
Wait a second… `__nbd_ioctl` calling `nbd_set_size` for `NBD_CLEAR_SOCK`? That seems odd. It makes intuitive sense for size and block size-setting. But clearing the socket? That warrants a closer look. I need to refresh my memory and check out how `__nbd_ioctl` is implemented to understand the relationship between clearing a socket and potentially modifying device size or block size. There must be some connection I'm missing, or maybe an artifact of socket cleanup needs device size to be reset? Time to dive into the `__nbd_ioctl` code.
|
| 91/2 |
2026/05/31 01:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:__nbd_ioctl]
Results: map[SourceCode:1581: /* Must be called with config_lock held */
1582: static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
1583: unsigned int cmd, unsigned long arg)
1584: {
1585: struct nbd_config *config = nbd->config;
1586: loff_t bytesize;
1587:
1588: switch (cmd) {
1589: case NBD_DISCONNECT:
1590: return nbd_disconnect(nbd);
1591: case NBD_CLEAR_SOCK:
1592: nbd_clear_sock_ioctl(nbd);
1593: return 0;
1594: case NBD_SET_SOCK:
1595: return nbd_add_socket(nbd, arg, false);
1596: case NBD_SET_BLKSIZE:
1597: return nbd_set_size(nbd, config->bytesize, arg);
1598: case NBD_SET_SIZE:
1599: return nbd_set_size(nbd, arg, nbd_blksize(config));
1600: case NBD_SET_SIZE_BLOCKS:
1601: if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
1602: return -EINVAL;
1603: return nbd_set_size(nbd, bytesize, nbd_blksize(config));
1604: case NBD_SET_TIMEOUT:
1605: nbd_set_cmd_timeout(nbd, arg);
1606: return 0;
1607:
1608: case NBD_SET_FLAGS:
1609: config->flags = arg;
1610: return 0;
1611: case NBD_DO_IT:
1612: return nbd_start_device_ioctl(nbd);
1613: case NBD_CLEAR_QUE:
1614: /*
1615: * This is for compatibility only. The queue is always cleared
1616: * by NBD_DO_IT or NBD_CLEAR_SOCK.
1617: */
1618: return 0;
1619: case NBD_PRINT_DEBUG:
1620: /*
1621: * For compatibility only, we no longer keep a list of
1622: * outstanding requests.
1623: */
1624: return 0;
1625: }
1626: return -ENOTTY;
1627: }
SourceFile:drivers/block/nbd.c]
|
| 92/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 70949
output: 40
thoughts: 61
Thoughts: **Investigating the Socket Clearing Function**
Okay, so I'm diving into this `NBD_CLEAR_SOCK` operation. My initial thought was that it directly calls `nbd_clear_sock_ioctl`. However, I need to be more precise in my understanding of the system. I am now considering a potential pathway: what if `nbd_clear_sock_ioctl` in turn *itself* is responsible for calling `nbd_set_size`? That would be interesting, and explain this behaviour I am seeing, and would need verifying.
Given this possibility, the next step is crystal clear: I need to scrutinize the code within `nbd_clear_sock_ioctl`. I must verify what it's actually doing and confirm, or rule out, this potential call to `nbd_set_size`. Time to roll up my sleeves and get into the code!
|
| 93/2 |
2026/05/31 01:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_clear_sock_ioctl]
Results: map[SourceCode:1562: static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
1563: {
1564: nbd_clear_sock(nbd);
1565: disk_force_media_change(nbd->disk);
1566: nbd_bdev_reset(nbd);
1567: if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
1568: &nbd->config->runtime_flags))
1569: nbd_config_put(nbd);
1570: }
SourceFile:drivers/block/nbd.c]
|
| 94/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 71431
output: 37
thoughts: 60
Thoughts: **Investigating a Potential Block Size Reset**
Okay, so I'm looking at `nbd_clear_sock_ioctl`, and it calls `disk_force_media_change` on the `nbd->disk`. My immediate thought is, "Does that function potentially reset the `logical_block_size` attribute associated with that disk?" I need to understand that side effect, and potential impact it could have. It's crucial for the performance and behaviour of the NBD device, if `logical_block_size` is changing without explicit user action.
So, let's dive into the implementation of `disk_force_media_change` and see exactly what it's doing. Time to dissect the code! I need to be sure before I move forward.
|
| 95/2 |
2026/05/31 01:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/genhd.c Name:disk_force_media_change]
Results: map[SourceCode: 286: /**
287: * disk_force_media_change - force a media change event
288: * @disk: the disk which will raise the event
289: *
290: * Should be called when the media changes for @disk. Generates a uevent
291: * and attempts to free all dentries and inodes and invalidates all block
292: * device page cache entries in that case.
293: */
294: void disk_force_media_change(struct gendisk *disk)
295: {
296: disk_event_uevent(disk, DISK_EVENT_MEDIA_CHANGE);
297: inc_diskseq(disk);
298: bdev_mark_dead(disk->part0, true);
299: set_bit(GD_NEED_PART_SCAN, &disk->state);
300: }
SourceFile:block/disk-events.c]
|
| 96/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 71970
output: 44
thoughts: 1627
Thoughts: **Debugging Block Size Alignment in NBD and UDF**
Okay, so I'm looking at this warning in `__getblk_slow` and `bdev_getblk`, and it's all about block size alignment. The goal is to figure out why `IS_ALIGNED` is failing. My initial thoughts are: does `bdev_mark_dead` or `bdev_logical_block_size` reset any block sizes? Nope, the first just sets a dead state, and the latter seems more stable.
The crucial question becomes: what if `bdev_logical_block_size` *isn't* the same as what the superblock sees? Specifically, what if `bdev_logical_block_size` is 4096, but `sb->s_blocksize` is 1024? `IS_ALIGNED(1024, 4096)` is definitely false. But how could `bdev_logical_block_size` *be* 4096? `nbd_set_size` is the most obvious, but the reproducer doesn't seem to call it, nor does it involve an NBD server sending a block size.
Then I realized, could `udf_fill_super` set `uopt->blocksize` to something other than the NBD default? What if it sets it to 512, then that gets passed to `sb_set_blocksize`, resulting in `sb->s_blocksize` also being 512? If `NBD_DO_IT` is happening concurrently, then `sb->s_blocksize` could be clobbered. But the reproducer is single-threaded, so that's not it.
So I re-examined the code. The problem is that `NBD_DO_IT` is being called *before* `mount`, so the block size being set by the NBD code is always 1024, and everything is aligned. I considered failures in `udf_load_vrs`, but that code eventually results in the block size being a multiple of 1024. Then I looked at the warning.
The warning traces back to `sb_bread` which calls `__bread_gfp`. This leads to `bdev_getblk`, where the critical check happens. And `size` which is used in `IS_ALIGNED` comes from `sb->s_blocksize`. So, if `sb->s_blocksize` is NOT a multiple of `bdev_logical_block_size(bdev)`, then we get a problem!
What if `bdev_logical_block_size(bdev)` is *larger* than `sb->s_blocksize`? That would definitely trigger the warning. I know that `udf_fill_super` initializes `uopt->blocksize` with the bdev's logical size. But, this sets the block size to the bdev's logical size. So if the logical size is 4096, then the superblock is initialized to the same value.
The next thought is, what if the logical block size changed *after* `sb_set_blocksize`? The `bdev_logical_block_size` could change to 1024 *after* `sb->s_blocksize` gets set. Then, `sb_bread` would be called with size 512, which is not aligned with 1024. But how can it change? It can't happen concurrently because the reproducer is single-threaded. I considered `recv_work`, but it doesn't modify block sizes. Is it `nbd_size_update` that is causing the trouble? Time to double-check where `nbd_set_size` is called.
|
| 97/2 |
2026/05/31 01:57 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:drivers/block/nbd.c IncludeSnippetLines:0 Name:nbd_set_size]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1597] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1599] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1603] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_genl_size_set SourceFile:drivers/block/nbd.c SourceLine:2058] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1529]] TruncatedOutput:false]
|
| 98/2 |
2026/05/31 01:57 |
llm |
expert |
0m
Model:
Tokens:
input: 74746
output: 44
thoughts: 1433
Thoughts: **Analyzing the NBD/UDF Vulnerability**
Okay, so I'm digging into this NBD and UDF issue. First thought, `nbd_genl_size_set` is netlink-based, but the reproducer isn't using netlink. That's a dead end. Next, I'm considering `nbd_start_device` being called by `NBD_DO_IT`. Yes, `NBD_DO_IT` does call it. But then `NBD_DO_IT` is called BEFORE the `mount` operation.
A potential roadblock: What if `NBD_DO_IT` called on `r[2]` BLOCKS? If the reproducer thread blocks, that's it. But wait, the reproducer uses syscalls like `mmap` and `ioctl`. Syzkaller reproducers often execute these in a test program. If a syscall blocks, sometimes the test program uses threads. However, syzkaller C reproducers generated with `syz_open_dev` and `syscall` are single-threaded UNLESS `pthread_create` is used. This one doesn't use `pthread_create`, so it's strictly single-threaded. If `NBD_DO_IT` blocks, the program hangs, and we never get to `mount`. But the crash is in `mount` (`udf_fill_super`), so we *know* it reaches that point. Therefore, `NBD_DO_IT` MUST return.
So, why does it return? Because `recv_work` fails and wakes it up. If `recv_work` fails, `nbd_start_device_ioctl` returns. Then `mount` is called. Then `logical_block_size` is 1024, and `sb_set_blocksize(sb, 1024)` is called. Then `IS_ALIGNED(1024, 1024)` is true! This is as expected!
But, the warning is triggered, which means the alignment is incorrect. Why? What if `udf_load_vrs` FAILS, and `uopt->blocksize` is doubled to 2048 or 4096? Then `sb_set_blocksize(sb, 2048)` or `sb_set_blocksize(sb, 4096)` is called. `IS_ALIGNED(2048, 1024)` and `IS_ALIGNED(4096, 1024)` are true respectively, so that doesn't explain it. What if `udf_load_vrs` FAILS for 4096? `udf_fill_super` will return an error, but the warning would NOT be triggered, so it MUST succeed.
Let's look at the warning:
```
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 __getblk_slow fs/buffer.c:1125 [inline]
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 bdev_getblk+0x580/0x660 fs/buffer.c:1461
```
`__getblk_slow` is called with a `size`. Where does `size` come from? `__bread_gfp` calls `bdev_getblk`, and `sb_bread` calls `__bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE)`. So, `size` is `sb->s_blocksize`.
If `size` is `sb->s_blocksize`, and `sb->s_blocksize` is a multiple of `bdev_logical_block_size(bdev)`, then `IS_ALIGNED(size, bdev_logical_block_size(bdev))` MUST be true. So, is there *any* way `sb->s_blocksize` is NOT a multiple of `bdev_logical_block_size(bdev)`? What if the logical block size is larger than the superblock block size?
For instance, if `bdev_logical_block_size(bdev)` is 4096, and `sb->s_blocksize` is 1024. But `udf_fill_super` initializes `uopt->blocksize = bdev_logical_block_size(sb->s_bdev)`. So, `uopt->blocksize` would be 4096. Then
|
| 99/2 |
2026/05/31 01:58 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:drivers/block/nbd.c IncludeSnippetLines:0 Name:nbd_set_size]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1597] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1599] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__nbd_ioctl SourceFile:drivers/block/nbd.c SourceLine:1603] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_genl_size_set SourceFile:drivers/block/nbd.c SourceLine:2058] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1529]] TruncatedOutput:false]
|
| 100/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 77528
output: 44
thoughts: 1433
Thoughts: **Analyzing the NBD/UDF Vulnerability**
Okay, so I'm digging into this NBD and UDF issue. First thought, `nbd_genl_size_set` is netlink-based, but the reproducer isn't using netlink. That's a dead end. Next, I'm considering `nbd_start_device` being called by `NBD_DO_IT`. Yes, `NBD_DO_IT` does call it. But then `NBD_DO_IT` is called BEFORE the `mount` operation.
A potential roadblock: What if `NBD_DO_IT` called on `r[2]` BLOCKS? If the reproducer thread blocks, that's it. But wait, the reproducer uses syscalls like `mmap` and `ioctl`. Syzkaller reproducers often execute these in a test program. If a syscall blocks, sometimes the test program uses threads. However, syzkaller C reproducers generated with `syz_open_dev` and `syscall` are single-threaded UNLESS `pthread_create` is used. This one doesn't use `pthread_create`, so it's strictly single-threaded. If `NBD_DO_IT` blocks, the program hangs, and we never get to `mount`. But the crash is in `mount` (`udf_fill_super`), so we *know* it reaches that point. Therefore, `NBD_DO_IT` MUST return.
So, why does it return? Because `recv_work` fails and wakes it up. If `recv_work` fails, `nbd_start_device_ioctl` returns. Then `mount` is called. Then `logical_block_size` is 1024, and `sb_set_blocksize(sb, 1024)` is called. Then `IS_ALIGNED(1024, 1024)` is true! This is as expected!
But, the warning is triggered, which means the alignment is incorrect. Why? What if `udf_load_vrs` FAILS, and `uopt->blocksize` is doubled to 2048 or 4096? Then `sb_set_blocksize(sb, 2048)` or `sb_set_blocksize(sb, 4096)` is called. `IS_ALIGNED(2048, 1024)` and `IS_ALIGNED(4096, 1024)` are true respectively, so that doesn't explain it. What if `udf_load_vrs` FAILS for 4096? `udf_fill_super` will return an error, but the warning would NOT be triggered, so it MUST succeed.
Let's look at the warning:
```
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 __getblk_slow fs/buffer.c:1125 [inline]
WARNING: CPU: 0 PID: 5719 at fs/buffer.c:1125 bdev_getblk+0x580/0x660 fs/buffer.c:1461
```
`__getblk_slow` is called with a `size`. Where does `size` come from? `__bread_gfp` calls `bdev_getblk`, and `sb_bread` calls `__bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE)`. So, `size` is `sb->s_blocksize`.
If `size` is `sb->s_blocksize`, and `sb->s_blocksize` is a multiple of `bdev_logical_block_size(bdev)`, then `IS_ALIGNED(size, bdev_logical_block_size(bdev))` MUST be true. So, is there *any* way `sb->s_blocksize` is NOT a multiple of `bdev_logical_block_size(bdev)`? What if the logical block size is larger than the superblock block size?
For instance, if `bdev_logical_block_size(bdev)` is 4096, and `sb->s_blocksize` is 1024. But `udf_fill_super` initializes `uopt->blocksize = bdev_logical_block_size(sb->s_bdev)`. So, `uopt->blocksize` would be 4096. Then
|
| 101/2 |
2026/05/31 01:58 |
tool |
codesearch-find-references |
0m
Error:
Args: map[ContextFile:drivers/block/nbd.c IncludeSnippetLines:0 Name:nbd_set_size]
|
| 102/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 80101
output: 45
thoughts: 2000
Thoughts: **Analyzing the Potential Block Size Mismatch in the NBD Driver**
Okay, let's break this down. My initial thought is: what if `NBD_DO_IT` is skipped, but `NBD_SET_SOCK` is called? The reproducer uses both commands. What if `NBD_DO_IT` fails *before* `nbd_set_size` is called? If that happens, then `logical_block_size` stays at 512. The `mount` is then called with `uopt->blocksize` as 512, which in turn calls `sb_set_blocksize(sb, 512)`. So `logical_block_size` would still be 512. This makes `IS_ALIGNED(512, 512)` true and the warning would not occur. What if `NBD_DO_IT` is not concurrent, but `mount` is? Then I must consider that the syzkaller reproducers are sometimes executed in a loop. So, it must be the case that `NBD_DO_IT` does return and `mount` gets called.
Looking at the syzkaller C code, I notice it's single-threaded, which seems to rule out immediate concurrency issues between these two calls. It also seems the `NBD_DO_IT` blocks, then `mount` is never called. However, it *is* called. So, `NBD_DO_IT` *must* return. Is it possible that `NBD_DO_IT` returns, but leaves a background thread running? Yes, `recv_work` runs in a workqueue! But, `recv_work` does *not* change `logical_block_size`.
But, what if `recv_work` calls `nbd_config_put` and that frees `config`? Would `logical_block_size` change in that case? No, `nbd_config_put` doesn't change `logical_block_size`.
What if `mount` calls `nbd_open`, which then calls `nbd_alloc_and_init_config`? `nbd_alloc_and_init_config` does set `config->blksize_bits = 10`. It doesn't call `nbd_set_size`, which leaves `logical_block_size` as 1024, if `NBD_DO_IT` did run. If `NBD_DO_IT` never ran, then `logical_block_size` would be 512. Then `mount` will call `nbd_open`. `nbd_open` allocates `config`, sets `config->blksize_bits = 10`, but it does *not* call `nbd_set_size`. So `logical_block_size` remains at 512. `udf_fill_super` sets `uopt->blocksize = 512` and calls `sb_set_blocksize(sb, 512)`. So `IS_ALIGNED(512, 512)` is true.
What if `udf_fill_super` calls `udf_load_vrs` with `uopt->blocksize = 512`. `udf_load_vrs` calls `sb_set_blocksize(sb, 512)`. Then `udf_load_vrs` reads blocks. `udf_load_vrs` FAILS. Then `uopt->blocksize` is doubled to 1024. Then `sb_set_blocksize(sb, 1024)` is called. Then `udf_load_vrs` is called with 1024. `sb_bread` is then called with `size=1024`. So, `IS_ALIGNED(1024, 512)` is true.
What if `udf_load_vrs` fails for 1024, 2048, and 4096? Then `udf_fill_super` returns an error, but the warning still triggers!
Let's look at that warning again: `__getblk_slow` and `bdev_getblk`. What's `size`? `__bread_gfp` calls `bdev_getblk(bdev, block, size, gfp)`. `sb_bread` calls `__bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE)`. So, `size` *is* `sb->s_
|
| 103/2 |
2026/05/31 01:58 |
tool |
codesearch-find-references |
0m
Error:
Args: map[ContextFile:drivers/block/nbd.c IncludeSnippetLines:0 Name:nbd_set_size]
|
| 104/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 83309
output: 35
thoughts: 174
Thoughts: **Investigating Potential Causes of Block Size Changes**
Okay, I've already confirmed that `nbd_set_size` is only called from within `__nbd_ioctl`, `nbd_genl_size_set`, and `nbd_start_device`. But a nagging thought persists – what if the `bdev_logical_block_size(bdev)` is being altered by *something* other than NBD itself? I need to rule out external influences.
Let me think… is there *any* other ioctl that's capable of modifying `logical_block_size`? I remember `BLKBSZSET` which *sets* the block size, but that calls `set_blocksize`, and that function appears to modify `inode->i_blkbits`, not `logical_block_size` as I'm checking. So, `BLKBSZSET` seems unrelated.
Hmm... What about `BLKFBSZSET`? Is that the culprit? Does *that* set the physical block size... no, wait a second. Is `BLKFBSZSET` the one that sets `logical_block_size`? I need to double-check `BLKFBSZSET`. Let's delve into that one, right now.
|
| 105/2 |
2026/05/31 01:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/ioctl.c Name:blkdev_common_ioctl]
Results: map[SourceCode: 559: /*
560: * Common commands that are handled the same way on native and compat
561: * user space. Note the separate arg/argp parameters that are needed
562: * to deal with the compat_ptr() conversion.
563: */
564: static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
565: unsigned int cmd, unsigned long arg,
566: void __user *argp)
567: {
568: unsigned int max_sectors;
569:
570: switch (cmd) {
571: case BLKFLSBUF:
572: return blkdev_flushbuf(bdev, cmd, arg);
573: case BLKROSET:
574: return blkdev_roset(bdev, cmd, arg);
575: case BLKDISCARD:
576: return blk_ioctl_discard(bdev, mode, arg);
577: case BLKSECDISCARD:
578: return blk_ioctl_secure_erase(bdev, mode, argp);
579: case BLKZEROOUT:
580: return blk_ioctl_zeroout(bdev, mode, arg);
581: case BLKGETDISKSEQ:
582: return put_u64(argp, bdev->bd_disk->diskseq);
583: case BLKREPORTZONE:
584: return blkdev_report_zones_ioctl(bdev, cmd, arg);
585: case BLKRESETZONE:
586: case BLKOPENZONE:
587: case BLKCLOSEZONE:
588: case BLKFINISHZONE:
589: return blkdev_zone_mgmt_ioctl(bdev, mode, cmd, arg);
590: case BLKGETZONESZ:
591: return put_uint(argp, bdev_zone_sectors(bdev));
592: case BLKGETNRZONES:
593: return put_uint(argp, bdev_nr_zones(bdev));
594: case BLKROGET:
595: return put_int(argp, bdev_read_only(bdev) != 0);
596: case BLKSSZGET: /* get block device logical block size */
597: return put_int(argp, bdev_logical_block_size(bdev));
598: case BLKPBSZGET: /* get block device physical block size */
599: return put_uint(argp, bdev_physical_block_size(bdev));
600: case BLKIOMIN:
601: return put_uint(argp, bdev_io_min(bdev));
602: case BLKIOOPT:
603: return put_uint(argp, bdev_io_opt(bdev));
604: case BLKALIGNOFF:
605: return put_int(argp, bdev_alignment_offset(bdev));
606: case BLKDISCARDZEROES:
607: return put_uint(argp, 0);
608: case BLKSECTGET:
609: max_sectors = min_t(unsigned int, USHRT_MAX,
610: queue_max_sectors(bdev_get_queue(bdev)));
611: return put_ushort(argp, max_sectors);
612: case BLKROTATIONAL:
613: return put_ushort(argp, !bdev_nonrot(bdev));
614: case BLKRASET:
615: case BLKFRASET:
616: if(!capable(CAP_SYS_ADMIN))
617: return -EACCES;
618: bdev->bd_disk->bdi->ra_pages = (arg * 512) / PAGE_SIZE;
619: return 0;
620: case BLKRRPART:
621: if (!capable(CAP_SYS_ADMIN))
622: return -EACCES;
623: if (bdev_is_partition(bdev))
624: return -EINVAL;
625: return disk_scan_partitions(bdev->bd_disk,
626: mode | BLK_OPEN_STRICT_SCAN);
627: case BLKTRACESTART:
628: case BLKTRACESTOP:
629: case BLKTRACETEARDOWN:
630: return blk_trace_ioctl(bdev, cmd, argp);
631: case BLKCRYPTOIMPORTKEY:
632: case BLKCRYPTOGENERATEKEY:
633: case BLKCRYPTOPREPAREKEY:
634: return blk_crypto_ioctl(bdev, cmd, argp);
635: case IOC_PR_REGISTER:
636: return blkdev_pr_register(bdev, mode, argp);
637: case IOC_PR_RESERVE:
638: return blkdev_pr_reserve(bdev, mode, argp);
639: case IOC_PR_RELEASE:
640: return blkdev_pr_release(bdev, mode, argp);
641: case IOC_PR_PREEMPT:
642: return blkdev_pr_preempt(bdev, mode, argp, false);
643: case IOC_PR_PREEMPT_ABORT:
644: return blkdev_pr_preempt(bdev, mode, argp, true);
645: case IOC_PR_CLEAR:
646: return blkdev_pr_clear(bdev, mode, argp);
647: default:
648: return blk_get_meta_cap(bdev, cmd, argp);
649: }
650: }
SourceFile:block/ioctl.c]
|
| 106/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 85469
output: 33
thoughts: 15
Thoughts: Okay, here's my interpretation of that:
**Investigating a Block Device IOCTL Call**
Alright, let's see. My current focus is definitely on `blkdev_ioctl`. I've got my mind on this function, and I'm zeroing in on a very specific element within it: `BLKBSZSET`. This suggests we're dealing with setting the block size of a block device. I need to understand what's happening when this command is issued. What parameters are involved? What checks are in place? Are there any potential security vulnerabilities here? I need to think through the implications of modifying the block size and how the kernel handles it. Gotta check the surrounding code for how this value is used later and look for any interesting side effects. My gut tells me there's something to investigate here.
|
| 107/2 |
2026/05/31 01:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/ioctl.c Name:blkdev_ioctl]
Results: map[SourceCode: 652: /*
653: * Always keep this in sync with compat_blkdev_ioctl()
654: * to handle all incompatible commands in both functions.
655: *
656: * New commands must be compatible and go into blkdev_common_ioctl
657: */
658: long blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
659: {
660: struct block_device *bdev = I_BDEV(file->f_mapping->host);
661: void __user *argp = (void __user *)arg;
662: blk_mode_t mode = file_to_blk_mode(file);
663: int ret;
664:
665: switch (cmd) {
666: /* These need separate implementations for the data structure */
667: case HDIO_GETGEO:
668: return blkdev_getgeo(bdev, argp);
669: case BLKPG:
670: return blkpg_ioctl(bdev, argp);
671:
672: /* Compat mode returns 32-bit data instead of 'long' */
673: case BLKRAGET:
674: case BLKFRAGET:
675: if (!argp)
676: return -EINVAL;
677: return put_long(argp,
678: (bdev->bd_disk->bdi->ra_pages * PAGE_SIZE) / 512);
679: case BLKGETSIZE:
680: if (bdev_nr_sectors(bdev) > ~0UL)
681: return -EFBIG;
682: return put_ulong(argp, bdev_nr_sectors(bdev));
683:
684: /* The data is compatible, but the command number is different */
685: case BLKBSZGET: /* get block device soft block size (cf. BLKSSZGET) */
686: return put_int(argp, block_size(bdev));
687: case BLKBSZSET:
688: return blkdev_bszset(file, mode, argp);
689: case BLKGETSIZE64:
690: return put_u64(argp, bdev_nr_bytes(bdev));
691:
692: /* Incompatible alignment on i386 */
693: case BLKTRACESETUP:
694: return blk_trace_ioctl(bdev, cmd, argp);
695: default:
696: break;
697: }
698:
699: ret = blkdev_common_ioctl(bdev, mode, cmd, arg, argp);
700: if (ret != -ENOIOCTLCMD)
701: return ret;
702:
703: if (!bdev->bd_disk->fops->ioctl)
704: return -ENOTTY;
705: return bdev->bd_disk->fops->ioctl(bdev, mode, cmd, arg);
706: }
SourceFile:block/ioctl.c]
|
| 108/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 86613
output: 40
thoughts: 1902
Thoughts: **Debugging a UDF Filesystem Block Size Mismatch**
Okay, let's break this down. It seems we have a UDF filesystem issue related to block sizes. It starts with a `BLKBSZSET` call, which eventually leads to `set_blocksize`, but doesn't touch the `logical_block_size` directly. The core of the problem seems to be an alignment issue. We're looking at a scenario where `bdev_logical_block_size(bdev)` (the device's logical block size) might differ from `sb->s_blocksize` (the superblock's block size), and that this *might* be unaligned.
Initially, I consider cases where the device's logical block size is different to the filesystem's block size, and that this could be unaligned.
I then check `udf_fill_super`. It *should* initialize the superblock's blocksize (`sb->s_blocksize`) correctly based on the device's logical block size. Specifically, it initializes `uopt->blocksize = bdev_logical_block_size(sb->s_bdev)`, and later calls `sb_set_blocksize(sb, uopt->blocksize)`. So, `sb->s_blocksize` should match the device's logical block size (unless the user explicitly passes bs=512 via `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)`). But the reproducer doesn't do this.
My first thought is there's a race condition. If `bdev_logical_block_size(sb->s_bdev)` changes *after* `uopt->blocksize` is initialized, we have a problem. This might occur if a function like `NBD_DO_IT` runs in parallel with a mount command.
However, the reproducer is *single-threaded*. I examine the system call sequence again, and consider different scenarios. I contemplate interrupting an ioctl call, which might lead to the issue. But, I don't see any explicit calls changing these block sizes. In addition, I consider the possibility of interrupt `NBD_DO_IT`, but it appears that it is called before `nbd_set_size`.
Thinking about the code, I consider interrupt `NBD_DO_IT`, but in that case, the block size is never changed, so I'm back at square one.
Could `recv_work` and `mount` happen at the same time? If `NBD_DO_IT` is interrupted, `recv_work` might *still* be running. `recv_work` calls `nbd_config_put`. However, `nbd_config_put` does NOT change `logical_block_size`.
Now, I revisit the `udf_fill_super` path. I confirm that it sets the block size correctly and then moves to the code that calls `udf_load_vrs` which also sets the block size, which then calls `udf_check_anchor_block` which reads the data using `sb_bread`. This results in `__bread_gfp` calling `__getblk_slow`. In these calls, `IS_ALIGNED` should be true.
It seemed that I might have found something with an offset in the anchor block, so I check that path and ensure the size is consistent.
I examine the warning again and confirm the call stack: `__getblk_slow` -> `bdev_getblk` -> `__bread_gfp` -> `sb_bread` -> `udf_read_tagged` -> `udf_check_anchor_block`. However, at this point, I don't see anywhere else where a different block size is used. This block size check happens *everywhere* that a block is read.
|
| 109/2 |
2026/05/31 01:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:udf_check_anchor_block]
Results: map[SourceCode:1898: /*
1899: * Check whether there is an anchor block in the given block and
1900: * load Volume Descriptor Sequence if so.
1901: *
1902: * Returns <0 on error, 0 on success, -EAGAIN is special - try next anchor
1903: * block
1904: */
1905: static int udf_check_anchor_block(struct super_block *sb, sector_t block,
1906: struct kernel_lb_addr *fileset)
1907: {
1908: struct buffer_head *bh;
1909: uint16_t ident;
1910: int ret;
1911:
1912: bh = udf_read_tagged(sb, block, block, &ident);
1913: if (!bh)
1914: return -EAGAIN;
1915: if (ident != TAG_IDENT_AVDP) {
1916: brelse(bh);
1917: return -EAGAIN;
1918: }
1919: ret = udf_load_sequence(sb, bh, fileset);
1920: brelse(bh);
1921: return ret;
1922: }
SourceFile:fs/udf/super.c]
|
| 110/2 |
2026/05/31 01:58 |
llm |
expert |
0m
Model:
Tokens:
input: 89769
output: 34
thoughts: 1052
Thoughts: **Analyzing a Potential Block Size Alignment Issue**
Okay, let me think this through. `udf_read_tagged` calls `sb_bread`, and `sb_bread` uses `sb->s_blocksize`. So, the critical variable `size` in our problematic `IS_ALIGNED` check is essentially `sb->s_blocksize`. The crux is understanding when this check *should* be false. The check `IS_ALIGNED(size, bdev_logical_block_size(bdev))` is testing if `sb->s_blocksize` is aligned with the underlying device's logical block size. If the check is FALSE, that means `sb->s_blocksize` is *not* aligned.
How can that happen? The logical possibility is that `bdev_logical_block_size(bdev)` is larger than `sb->s_blocksize`. For instance, the file system sees the block as 512, while the underlying device considers the block size to be 1024. But wait, `udf_fill_super` *initializes* `uopt->blocksize` to `bdev_logical_block_size(sb->s_bdev)`. So, `uopt->blocksize` should inherit the device's block size. Then we call `sb_set_blocksize(sb, 1024)`, which means `sb->s_blocksize` *should* also become 1024. Therefore, it's impossible for `sb->s_blocksize` to be 512!
Could the underlying device's block size change *after* `udf_fill_super` starts, but *before* the file system uses it? Yes, if some external process, perhaps `NBD_DO_IT` could set the size to 1024, or a larger number. The key is concurrency. But, the reproducer is supposedly single-threaded. Hmm.
Could something else happen? What if, `NBD_DO_IT` changes the logical block size to, say, 1024, *before* the mount. `mount` is called. `udf_fill_super` initializes `uopt->blocksize = 1024`. `sb_set_blocksize(sb, 1024)` is called. Then, `udf_load_vrs` is called and FAILS. Then, the code doubles `uopt->blocksize` to 2048, and calls `sb_set_blocksize(sb, 2048)`. `udf_load_vrs` FAILS again. Then block size becomes 4096.
This is the failure path. In all these cases, `sb->s_blocksize` *ends up* as either 1024, 2048, or 4096. All these values are multiples of 1024! So `IS_ALIGNED(size, 1024)` would *always* be TRUE! This means the warning should not trigger here!
What if the `bdev_logical_block_size(bdev)` is not 1024? What if it's 4096? `uopt->blocksize` would start at 4096, and then `sb_set_blocksize(sb, 4096)` is called. `IS_ALIGNED(4096, 4096)` is TRUE. What about 512? In that case, `uopt->blocksize` begins at 512, `sb_set_blocksize(sb, 512)` is called. And `IS_ALIGNED(512, 512)` is TRUE. Even if it's doubled to 1024, we still get `IS_ALIGNED(1024, 512)` being TRUE. So the alignment check is always TRUE. Therefore the warning should NEVER trigger. The alignment check should *always* evaluate as true. So, why does the warning happen? I need to review `__getblk_slow` and the stack trace again.
|
| 111/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/buffer.c Name:__getblk_slow]
Results: map[SourceCode:1119: static struct buffer_head *
1120: __getblk_slow(struct block_device *bdev, sector_t block,
1121: unsigned size, gfp_t gfp)
1122: {
1123: bool blocking = gfpflags_allow_blocking(gfp);
1124:
1125: if (WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))) {
1126: printk(KERN_ERR "getblk(): block size %d not aligned to logical block size %d\n",
1127: size, bdev_logical_block_size(bdev));
1128: return NULL;
1129: }
1130:
1131: for (;;) {
1132: struct buffer_head *bh;
1133:
1134: if (!grow_buffers(bdev, block, size, gfp))
1135: return NULL;
1136:
1137: if (blocking)
1138: bh = __find_get_block_nonatomic(bdev, block, size);
1139: else
1140: bh = __find_get_block(bdev, block, size);
1141: if (bh)
1142: return bh;
1143: }
1144: }
SourceFile:fs/buffer.c]
|
| 112/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 92188
output: 39
thoughts: 197
Thoughts: **Analyzing Potential Block Size Mismatches in UDF Filesystem**
Okay, so I'm trying to wrap my head around this block size situation. The code uses `size`, which seems to be tied to `sb->s_blocksize`. My initial thought is, could `size` *not* be a power of 2? That would be a problem. If it's not a power of 2, it's probably not aligned to the device's logical block size, `bdev_logical_block_size(bdev)`. However, `sb->s_blocksize` *should* be a power of 2 because `uopt->blocksize` starts at `bdev_logical_block_size(bdev)` (which is always a power of 2) and is subsequently doubled.
But then I remember the possibility that `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)` could be true! The reproducer, though, doesn't pass a `bs=` option, so that's not the issue. Then it hits me... what if `udf_load_vrs` is the culprit? Could it be calling `sb_set_blocksize` with a *different* size and throwing off the alignment? Time to go dig into `udf_load_vrs` and see what it's up to.
|
| 113/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:udf_load_vrs]
Results: map[SourceCode:1993: /*
1994: * Check Volume Structure Descriptor, find Anchor block and load Volume
1995: * Descriptor Sequence.
1996: *
1997: * Returns < 0 on error, 0 on success. -EAGAIN is special meaning anchor
1998: * block was not found.
1999: */
2000: static int udf_load_vrs(struct super_block *sb, struct udf_options *uopt,
2001: int silent, struct kernel_lb_addr *fileset)
2002: {
2003: struct udf_sb_info *sbi = UDF_SB(sb);
2004: int nsr = 0;
2005: int ret;
2006:
2007: if (!sb_set_blocksize(sb, uopt->blocksize)) {
2008: if (!silent)
2009: udf_warn(sb, "Bad block size\n");
2010: return -EINVAL;
2011: }
2012: sbi->s_last_block = uopt->lastblock;
2013: if (!UDF_QUERY_FLAG(sb, UDF_FLAG_NOVRS)) {
2014: /* Check that it is NSR02 compliant */
2015: nsr = udf_check_vsd(sb);
2016: if (!nsr) {
2017: if (!silent)
2018: udf_warn(sb, "No VRS found\n");
2019: return -EINVAL;
2020: }
2021: if (nsr == -1)
2022: udf_debug("Failed to read sector at offset %d. "
2023: "Assuming open disc. Skipping validity "
2024: "check\n", VSD_FIRST_SECTOR_OFFSET);
2025: if (!sbi->s_last_block)
2026: sbi->s_last_block = udf_get_last_block(sb);
2027: } else {
2028: udf_debug("Validity check skipped because of novrs option\n");
2029: }
2030:
2031: /* Look for anchor block and load Volume Descriptor Sequence */
2032: sbi->s_anchor = uopt->anchor;
2033: ret = udf_scan_anchors(sb, &sbi->s_last_block, fileset);
2034: if (ret < 0) {
2035: if (!silent && ret == -EAGAIN)
2036: udf_warn(sb, "No anchor found\n");
2037: return ret;
2038: }
2039: return 0;
2040: }
SourceFile:fs/udf/super.c]
|
| 114/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 93518
output: 39
thoughts: 81
Thoughts: Okay, let me think this through.
**Analyzing Block Size Consistency in UDF Filesystem Operations**
Right, so `udf_load_vrs` is setting the block size for the superblock using `sb_set_blocksize` based on `uopt->blocksize`. Importantly, it seems like that's the *only* place it does that. The superblock's block size (`sb->s_blocksize`) isn't being modified again after this initial setting within `udf_load_vrs`.
But hold on a second... what if something *else* is using a different block size? My concern is that there might be inconsistencies lurking. Specifically, I need to consider `udf_check_vsd`. It's possible that this function, during the verification process, could call `sb_bread` with a different size altogether, potentially leading to misalignment or unexpected behavior. I need to dive into `udf_check_vsd` and see what it's actually doing with block sizes to confirm.
|
| 115/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:udf_check_vsd]
Results: map[SourceCode: 732: /*
733: * Check Volume Structure Descriptors (ECMA 167 2/9.1)
734: * We also check any "CD-ROM Volume Descriptor Set" (ECMA 167 2/8.3.1)
735: * @return 1 if NSR02 or NSR03 found,
736: * -1 if first sector read error, 0 otherwise
737: */
738: static int udf_check_vsd(struct super_block *sb)
739: {
740: struct volStructDesc *vsd = NULL;
741: loff_t sector = VSD_FIRST_SECTOR_OFFSET;
742: int sectorsize;
743: struct buffer_head *bh = NULL;
744: int nsr = 0;
745: struct udf_sb_info *sbi;
746: loff_t session_offset;
747:
748: sbi = UDF_SB(sb);
749: if (sb->s_blocksize < sizeof(struct volStructDesc))
750: sectorsize = sizeof(struct volStructDesc);
751: else
752: sectorsize = sb->s_blocksize;
753:
754: session_offset = (loff_t)sbi->s_session << sb->s_blocksize_bits;
755: sector += session_offset;
756:
757: udf_debug("Starting at sector %u (%lu byte sectors)\n",
758: (unsigned int)(sector >> sb->s_blocksize_bits),
759: sb->s_blocksize);
760: /* Process the sequence (if applicable). The hard limit on the sector
761: * offset is arbitrary, hopefully large enough so that all valid UDF
762: * filesystems will be recognised. There is no mention of an upper
763: * bound to the size of the volume recognition area in the standard.
764: * The limit will prevent the code to read all the sectors of a
765: * specially crafted image (like a bluray disc full of CD001 sectors),
766: * potentially causing minutes or even hours of uninterruptible I/O
767: * activity. This actually happened with uninitialised SSD partitions
768: * (all 0xFF) before the check for the limit and all valid IDs were
769: * added */
770: for (; !nsr && sector < VSD_MAX_SECTOR_OFFSET; sector += sectorsize) {
771: /* Read a block */
772: bh = sb_bread(sb, sector >> sb->s_blocksize_bits);
773: if (!bh)
774: break;
775:
776: vsd = (struct volStructDesc *)(bh->b_data +
777: (sector & (sb->s_blocksize - 1)));
778: nsr = identify_vsd(vsd);
779: /* Found NSR or end? */
780: if (nsr) {
781: brelse(bh);
782: break;
783: }
784: /*
785: * Special handling for improperly formatted VRS (e.g., Win10)
786: * where components are separated by 2048 bytes even though
787: * sectors are 4K
788: */
789: if (sb->s_blocksize == 4096) {
790: nsr = identify_vsd(vsd + 1);
791: /* Ignore unknown IDs... */
792: if (nsr < 0)
793: nsr = 0;
794: }
795: brelse(bh);
796: }
797:
798: if (nsr > 0)
799: return 1;
800: else if (!bh && sector - session_offset == VSD_FIRST_SECTOR_OFFSET)
801: return -1;
802: else
803: return 0;
804: }
SourceFile:fs/udf/super.c]
|
| 116/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 95069
output: 40
thoughts: 1400
Thoughts: **Analyzing a Potential Block Size Alignment Issue in UDF Filesystems**
Okay, let's break this down. I'm looking at a scenario where `udf_check_vsd` calls `sb_bread`, which uses `sb->s_blocksize`. The key question here is whether `sb->s_blocksize` is aligned with `bdev_logical_block_size(bdev)`. I initially proved that it *should* always be a multiple, unless `bdev_logical_block_size(bdev)` changes *after* `sb_set_blocksize`.
The warning is triggered when `size` (which ends up being 512) is *not* aligned to `bdev_logical_block_size(bdev)`, which means the logical block size of the device must be *greater* than 512. Therefore `bdev_logical_block_size(bdev)` must have changed.
The reproducer shows a sequence: `NBD_DO_IT` then `mount`. `NBD_DO_IT` calls `nbd_start_device` which calls `nbd_set_size`. This sets the logical block size. If `NBD_DO_IT` is called CONCURRENTLY with the mount, it could explain a change in the block size from 512 to 1024 while mount is running, however the reproducer is single-threaded.
I'm now considering if `NBD_DO_IT` *doesn't* block, and a background thread handles the block size change. However, that's not possible because `nbd_set_size` is synchronous in `nbd_start_device`.
Let's consider these possibilities, and try to construct the correct execution order. If `NBD_DO_IT` sets the logical block size to 1024, *then* `mount` is called, and `uopt->blocksize` is initialized to 1024, everything is aligned; `IS_ALIGNED(1024, 1024)` is true.
The *only* potential is if the block size changed *after* mount starts! But, the reproducer does not call close on the relevant file descriptor.
What about `recv_work`, can it call `nbd_config_put` and free `config`? Would this affect `logical_block_size`? No.
What if `mount` calls `nbd_open`, which calls `nbd_alloc_and_init_config`? This sets `config->blksize_bits = 10` (1024). But `nbd_alloc_and_init_config` does NOT call `nbd_set_size`, which means the `logical_block_size` remains at 1024.
If `NBD_DO_IT` is not called, then `logical_block_size` remains at 512. When `mount` occurs, `uopt->blocksize` is 512 and `IS_ALIGNED(512, 512)` is true.
In all these scenarios, alignment *should* be true. Therefore, the warning should never trigger. It's unclear how this is failing... Let's re-examine `bdev_logical_block_size(bdev)`.
|
| 117/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/blkdev.h Name:bdev_logical_block_size]
Results: map[SourceCode:1367: static inline unsigned int bdev_logical_block_size(struct block_device *bdev)
1368: {
1369: return queue_logical_block_size(bdev_get_queue(bdev));
1370: }
SourceFile:include/linux/blkdev.h]
|
| 118/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 97344
output: 38
thoughts: 1366
Thoughts: **Analyzing Potential Block Size Mismatches in UDF Filesystem Mounting**
Okay, so I'm diving into this UDF filesystem mounting issue. First, I need to make sure I'm not missing anything obvious in the basic setup. Is `bdev_get_queue(bdev)` potentially returning NULL? No, that's not it. Okay, what about `queue_logical_block_size` giving us something unexpected? That looks safe.
Now, let's get into the heart of the matter: `sb->s_blocksize`. My initial thought is, what if this isn't one of the standard sizes (512, 1024, 2048, or 4096)? And, let's not overlook the edge case of zero, or even a value of one. If `sb->s_blocksize` is zero, the `IS_ALIGNED` macro actually evaluates to TRUE which seems wrong, but okay. If it's one, `IS_ALIGNED(1, 1024)` is false. But, how can `sb->s_blocksize` be set to 1? `udf_fill_super` sets it to `bdev_logical_block_size(sb->s_bdev)`. Hmm. But, that's validated by `blk_validate_block_size` to be at least 512! Unless... unless `uopt->flags` has `UDF_FLAG_BLOCKSIZE_SET` set and `uopt->blocksize` is 1 somehow. But the reproducer doesn't seem to pass `bs=1`, so that's probably not it.
Okay, let's step through a hypothetical where `udf_load_vrs` is called and sets `uopt->blocksize` to 1024. Then `sb_set_blocksize(sb, 1024)` is called, so `sb->s_blocksize` becomes 1024. Then we hit `udf_check_anchor_block`, call `udf_read_tagged`, and `sb_bread(sb, block)`. What if `block` is `0xFFFFFFFF`? A quick check in `udf_read_tagged` confirms that it handles that and returns NULL, so no big deal there. What if it's something else?
Now here's a crucial question: What if `bdev_logical_block_size(bdev)` is 2048, but `sb->s_blocksize` is only 1024? How does that happen? Well, `NBD_DO_IT` sets `logical_block_size` to `1 << config->blksize_bits`. Initially, `config->blksize_bits` is 10 (1024). Can it be modified to 11 (2048)? Only if `NBD_SET_BLKSIZE` is called! But the reproducer code doesn't explicitly call `NBD_SET_BLKSIZE`.
Hold on... let me go back to the reproducer code and verify. The reproducer calls `0xab00` (`NBD_SET_SOCK`) and `0xab03` (`NBD_DO_IT`), but not `NBD_SET_BLKSIZE`.
Wait! `NBD_SET_SOCK` has `arg = r[1]` – and `r[1]` is the socket file descriptor. `NBD_DO_IT` gets called on `r[2]`. But `r[0]` and `r[2]` are *both* `/dev/nbd0` devices. And `r[2]` is opened *after* `r[0]`. The tricky bit is that `r[0]` uses `O_CLOEXEC` but `r[2]` does not. What happens if `NBD_DO_IT` is called, it correctly sets `logical_block_size` to 1024. Then `NBD_DO_IT` returns, the `mount` function is called, and at this point, the `logical_block_size` becomes 1024. Then `uopt->blocksize` is 1024, `sb_set_blocksize(sb, 1024)` is called. So, `IS_ALIGNED(1024, 1024)` is TRUE which is correct.
What if `udf_load_vrs` fails, and `uopt->blocksize` is doubled? First to 2048: that's still aligned. Then to 4
|
| 119/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/udf/super.c Name:udf_fill_super]
Results: map[SourceCode:2151: static int udf_fill_super(struct super_block *sb, struct fs_context *fc)
2152: {
2153: int ret = -EINVAL;
2154: struct inode *inode = NULL;
2155: struct udf_options *uopt = fc->fs_private;
2156: struct kernel_lb_addr rootdir, fileset;
2157: struct udf_sb_info *sbi;
2158: bool lvid_open = false;
2159: int silent = fc->sb_flags & SB_SILENT;
2160:
2161: sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
2162: if (!sbi)
2163: return -ENOMEM;
2164:
2165: sb->s_fs_info = sbi;
2166:
2167: mutex_init(&sbi->s_alloc_mutex);
2168:
2169: fileset.logicalBlockNum = 0xFFFFFFFF;
2170: fileset.partitionReferenceNum = 0xFFFF;
2171:
2172: sbi->s_flags = uopt->flags;
2173: sbi->s_uid = uopt->uid;
2174: sbi->s_gid = uopt->gid;
2175: sbi->s_umask = uopt->umask;
2176: sbi->s_fmode = uopt->fmode;
2177: sbi->s_dmode = uopt->dmode;
2178: sbi->s_nls_map = uopt->nls_map;
2179: uopt->nls_map = NULL;
2180: rwlock_init(&sbi->s_cred_lock);
2181:
2182: if (uopt->session == 0xFFFFFFFF)
2183: sbi->s_session = udf_get_last_session(sb);
2184: else
2185: sbi->s_session = uopt->session;
2186:
2187: udf_debug("Multi-session=%d\n", sbi->s_session);
2188:
2189: /* Fill in the rest of the superblock */
2190: sb->s_op = &udf_sb_ops;
2191: sb->s_export_op = &udf_export_ops;
2192:
2193: sb->s_magic = UDF_SUPER_MAGIC;
2194: sb->s_time_gran = 1000;
2195:
2196: if (uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)) {
2197: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2198: } else {
2199: uopt->blocksize = bdev_logical_block_size(sb->s_bdev);
2200: while (uopt->blocksize <= 4096) {
2201: ret = udf_load_vrs(sb, uopt, silent, &fileset);
2202: if (ret < 0) {
2203: if (!silent && ret != -EACCES) {
2204: pr_notice("Scanning with blocksize %u failed\n",
2205: uopt->blocksize);
2206: }
2207: brelse(sbi->s_lvid_bh);
2208: sbi->s_lvid_bh = NULL;
2209: /*
2210: * EACCES is special - we want to propagate to
2211: * upper layers that we cannot handle RW mount.
2212: */
2213: if (ret == -EACCES)
2214: break;
2215: } else
2216: break;
2217:
2218: uopt->blocksize <<= 1;
2219: }
2220: }
2221: if (ret < 0) {
2222: if (ret == -EAGAIN) {
2223: udf_warn(sb, "No partition found (1)\n");
2224: ret = -EINVAL;
2225: }
2226: goto error_out;
2227: }
2228:
2229: udf_debug("Lastblock=%u\n", sbi->s_last_block);
2230:
2231: if (sbi->s_lvid_bh) {
2232: struct logicalVolIntegrityDescImpUse *lvidiu =
2233: udf_sb_lvidiu(sb);
2234: uint16_t minUDFReadRev;
2235: uint16_t minUDFWriteRev;
2236:
2237: if (!lvidiu) {
2238: ret = -EINVAL;
2239: goto error_out;
2240: }
2241: minUDFReadRev = le16_to_cpu(lvidiu->minUDFReadRev);
2242: minUDFWriteRev = le16_to_cpu(lvidiu->minUDFWriteRev);
2243: if (minUDFReadRev > UDF_MAX_READ_VERSION) {
2244: udf_err(sb, "minUDFReadRev=%x (max is %x)\n",
2245: minUDFReadRev,
2246: UDF_MAX_READ_VERSION);
2247: ret = -EINVAL;
2248: goto error_out;
2249: } else if (minUDFWriteRev > UDF_MAX_WRITE_VERSION) {
2250: if (!sb_rdonly(sb)) {
2251: ret = -EACCES;
2252: goto error_out;
2253: }
2254: UDF_SET_FLAG(sb, UDF_FLAG_RW_INCOMPAT);
2255: }
2256:
2257: sbi->s_udfrev = minUDFWriteRev;
2258:
2259: if (minUDFReadRev >= UDF_VERS_USE_EXTENDED_FE)
2260: UDF_SET_FLAG(sb, UDF_FLAG_USE_EXTENDED_FE);
2261: if (minUDFReadRev >= UDF_VERS_USE_STREAMS)
2262: UDF_SET_FLAG(sb, UDF_FLAG_USE_STREAMS);
2263: }
2264:
2265: if (!sbi->s_partitions) {
2266: udf_warn(sb, "No partition found (2)\n");
2267: ret = -EINVAL;
2268: goto error_out;
2269: }
2270:
2271: if (sbi->s_partmaps[sbi->s_partition].s_partition_flags &
2272: UDF_PART_FLAG_READ_ONLY) {
2273: if (!sb_rdonly(sb)) {
2274: ret = -EACCES;
2275: goto error_out;
2276: }
2277: UDF_SET_FLAG(sb, UDF_FLAG_RW_INCOMPAT);
2278: }
2279:
2280: ret = udf_find_fileset(sb, &fileset, &rootdir);
2281: if (ret < 0) {
2282: udf_warn(sb, "No fileset found\n");
2283: goto error_out;
2284: }
2285:
2286: if (!silent) {
2287: struct timestamp ts;
2288: udf_time_to_disk_stamp(&ts, sbi->s_record_time);
2289: udf_info("Mounting volume '%s', timestamp %04u/%02u/%02u %02u:%02u (%x)\n",
2290: sbi->s_volume_ident,
2291: le16_to_cpu(ts.year), ts.month, ts.day,
2292: ts.hour, ts.minute, le16_to_cpu(ts.typeAndTimezone));
2293: }
2294: if (!sb_rdonly(sb)) {
2295: udf_open_lvid(sb);
2296: lvid_open = true;
2297: }
2298:
2299: /* Assign the root inode */
2300: /* assign inodes by physical block number */
2301: /* perhaps it's not extensible enough, but for now ... */
2302: inode = udf_iget(sb, &rootdir);
2303: if (IS_ERR(inode)) {
2304: udf_err(sb, "Error in udf_iget, block=%u, partition=%u\n",
2305: rootdir.logicalBlockNum, rootdir.partitionReferenceNum);
2306: ret = PTR_ERR(inode);
2307: goto error_out;
2308: }
2309:
2310: /* Allocate a dentry for the root inode */
2311: sb->s_root = d_make_root(inode);
2312: if (!sb->s_root) {
2313: udf_err(sb, "Couldn't allocate root dentry\n");
2314: ret = -ENOMEM;
2315: goto error_out;
2316: }
2317: sb->s_maxbytes = UDF_MAX_FILESIZE;
2318: sb->s_max_links = UDF_MAX_LINKS;
2319: return 0;
2320:
2321: error_out:
2322: iput(sbi->s_vat_inode);
2323: unload_nls(uopt->nls_map);
2324: if (lvid_open)
2325: udf_close_lvid(sb);
2326: brelse(sbi->s_lvid_bh);
2327: udf_sb_free_partitions(sb);
2328: kfree(sbi);
2329: sb->s_fs_info = NULL;
2330:
2331: return ret;
2332: }
SourceFile:fs/udf/super.c]
|
| 120/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 102735
output: 36
thoughts: 526
Thoughts: **Unraveling the Concurrency Conundrum**
Okay, let's break this down. My initial concern was about failures in `udf_load_vrs` and inconsistencies with `udf_fill_super`, but those scenarios are covered by the error handling. I also considered scenarios where block sizes might be mismatched between `udf_load_vrs` and `sb_bread`, but the block size is consistently defined.
Here's the critical realization: `udf_load_vrs` succeeds with `uopt->blocksize = 512`, so the superblock's `s_blocksize` is set to 512. Then, `udf_fill_super` continues, and, critically, `NBD_DO_IT` is called **concurrently**. I had to remember the reproducer is single-threaded. However, could there be ANY way `NBD_DO_IT` is called AFTER `mount`? No, the reproducer calls `NBD_DO_IT` before `mount`.
Aha! Syzkaller test programs! They frequently use separate threads for syscalls. If a syscall blocks, the thread is often killed or allowed to run in the background. Thus, if `NBD_DO_IT` is running in a BACKGROUND thread, it can call `nbd_set_size` **concurrently** with the `mount` process!
Here's where the magic happens: if `nbd_set_size` is called concurrently with `mount`, then `bdev_logical_block_size(bdev)` can change from 512 to 1024 **AFTER** `sb_set_blocksize(sb, 512)` is called. Then, `sb_bread` is called with `size=512`, and the alignment check fails because `IS_ALIGNED(512, 1024)` is FALSE! That's it! That explains the warning perfectly!
The root cause is a **data race / concurrent modification** of `logical_block_size` while the filesystem is mounted. The race condition occurs because of the concurrent execution of `NBD_DO_IT` and `mount`.
Now the question is privilege escalation: Does this need `CAP_SYS_ADMIN`? Let's check `nbd_ioctl`...
|
| 121/2 |
2026/05/31 01:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_ioctl]
Results: map[SourceCode:1629: static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
1630: unsigned int cmd, unsigned long arg)
1631: {
1632: struct nbd_device *nbd = bdev->bd_disk->private_data;
1633: struct nbd_config *config = nbd->config;
1634: int error = -EINVAL;
1635:
1636: if (!capable(CAP_SYS_ADMIN))
1637: return -EPERM;
1638:
1639: /* The block layer will pass back some non-nbd ioctls in case we have
1640: * special handling for them, but we don't so just return an error.
1641: */
1642: if (_IOC_TYPE(cmd) != 0xab)
1643: return -EINVAL;
1644:
1645: mutex_lock(&nbd->config_lock);
1646:
1647: /* Don't allow ioctl operations on a nbd device that was created with
1648: * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
1649: */
1650: if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
1651: (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
1652: error = __nbd_ioctl(bdev, nbd, cmd, arg);
1653: else
1654: dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
1655: mutex_unlock(&nbd->config_lock);
1656: return error;
1657: }
SourceFile:drivers/block/nbd.c]
|
| 122/2 |
2026/05/31 01:59 |
llm |
expert |
0m
Model:
Tokens:
input: 104334
output: 41
thoughts: 88
Thoughts: Okay, let me think this through.
**Analyzing NBD Security Considerations**
Right, so `nbd_ioctl` definitely needs `CAP_SYS_ADMIN` in the initial user namespace. That's because it relies on the `capable(CAP_SYS_ADMIN)` check, and not the more namespace-aware `ns_capable` function. But... hang on a minute. What about `nbd_genl_size_set`? I need to quickly determine if an unprivileged user can call this function through netlink. This is a potential vulnerability, and it's essential that I examine it closely. Let me pull up the code for `nbd_genl_size_set` and see what's going on.
|
| 123/2 |
2026/05/31 02:00 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_genl_size_set]
Results: map[SourceCode:2045: static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
2046: {
2047: struct nbd_config *config = nbd->config;
2048: u64 bsize = nbd_blksize(config);
2049: u64 bytes = config->bytesize;
2050:
2051: if (info->attrs[NBD_ATTR_SIZE_BYTES])
2052: bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);
2053:
2054: if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
2055: bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);
2056:
2057: if (bytes != config->bytesize || bsize != nbd_blksize(config))
2058: return nbd_set_size(nbd, bytes, bsize);
2059: return 0;
2060: }
SourceFile:drivers/block/nbd.c]
|
| 124/2 |
2026/05/31 02:00 |
llm |
expert |
1m
Model:
Tokens:
input: 104954
output: 40
thoughts: 31
Thoughts: Okay, here's my interpretation of those thoughts, framed as a first-person summary, keeping in mind my expertise:
**Tracing the Caller of `nbd_genl_size_set`**
Alright, I'm trying to figure out the calling context for `nbd_genl_size_set`. It's pretty clear that I need to backtrack through the code, particularly within the Netlink interface. I've got to find out *who* is responsible for calling this function. Okay, let me see...ah, that's right, it appears to be directly related to `nbd_genl_reconfigure`. Makes sense; changing the size of an NBD device at runtime would logically fall under reconfiguring it. This narrows the scope of my investigation significantly, which is what I was hoping for.
|
| 125/2 |
2026/05/31 02:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_genl_reconfigure]
Results: map[SourceCode:2298: static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
2299: {
2300: struct nbd_device *nbd = NULL;
2301: struct nbd_config *config;
2302: int index;
2303: int ret = 0;
2304: bool put_dev = false;
2305:
2306: if (!netlink_capable(skb, CAP_SYS_ADMIN))
2307: return -EPERM;
2308:
2309: if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
2310: pr_err("must specify a device to reconfigure\n");
2311: return -EINVAL;
2312: }
2313: index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2314: mutex_lock(&nbd_index_mutex);
2315: nbd = idr_find(&nbd_index_idr, index);
2316: if (!nbd) {
2317: mutex_unlock(&nbd_index_mutex);
2318: pr_err("couldn't find a device at index %d\n", index);
2319: return -EINVAL;
2320: }
2321: if (nbd->backend) {
2322: if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2323: if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2324: nbd->backend)) {
2325: mutex_unlock(&nbd_index_mutex);
2326: dev_err(nbd_to_dev(nbd),
2327: "backend image doesn't match with %s\n",
2328: nbd->backend);
2329: return -EINVAL;
2330: }
2331: } else {
2332: mutex_unlock(&nbd_index_mutex);
2333: dev_err(nbd_to_dev(nbd), "must specify backend\n");
2334: return -EINVAL;
2335: }
2336: }
2337: if (!refcount_inc_not_zero(&nbd->refs)) {
2338: mutex_unlock(&nbd_index_mutex);
2339: pr_err("device at index %d is going down\n", index);
2340: return -EINVAL;
2341: }
2342: mutex_unlock(&nbd_index_mutex);
2343:
2344: config = nbd_get_config_unlocked(nbd);
2345: if (!config) {
2346: dev_err(nbd_to_dev(nbd),
2347: "not configured, cannot reconfigure\n");
2348: nbd_put(nbd);
2349: return -EINVAL;
2350: }
2351:
2352: mutex_lock(&nbd->config_lock);
2353: if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
2354: !nbd->pid) {
2355: dev_err(nbd_to_dev(nbd),
2356: "not configured, cannot reconfigure\n");
2357: ret = -EINVAL;
2358: goto out;
2359: }
2360:
2361: ret = nbd_genl_size_set(info, nbd);
2362: if (ret)
2363: goto out;
2364:
2365: if (info->attrs[NBD_ATTR_TIMEOUT])
2366: nbd_set_cmd_timeout(nbd,
2367: nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2368: if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2369: config->dead_conn_timeout =
2370: nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2371: config->dead_conn_timeout *= HZ;
2372: }
2373: if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2374: u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2375: if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2376: if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2377: &nbd->flags))
2378: put_dev = true;
2379: } else {
2380: if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2381: &nbd->flags))
2382: refcount_inc(&nbd->refs);
2383: }
2384:
2385: if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2386: set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2387: &config->runtime_flags);
2388: } else {
2389: clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2390: &config->runtime_flags);
2391: }
2392: }
2393:
2394: if (info->attrs[NBD_ATTR_SOCKETS]) {
2395: struct nlattr *attr;
2396: int rem, fd;
2397:
2398: nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2399: rem) {
2400: struct nlattr *socks[NBD_SOCK_MAX+1];
2401:
2402: if (nla_type(attr) != NBD_SOCK_ITEM) {
2403: pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2404: ret = -EINVAL;
2405: goto out;
2406: }
2407: ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2408: attr,
2409: nbd_sock_policy,
2410: info->extack);
2411: if (ret != 0) {
2412: pr_err("error processing sock list\n");
2413: ret = -EINVAL;
2414: goto out;
2415: }
2416: if (!socks[NBD_SOCK_FD])
2417: continue;
2418: fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2419: ret = nbd_reconnect_socket(nbd, fd);
2420: if (ret) {
2421: if (ret == -ENOSPC)
2422: ret = 0;
2423: goto out;
2424: }
2425: dev_info(nbd_to_dev(nbd), "reconnected socket\n");
2426: }
2427: }
2428: out:
2429: mutex_unlock(&nbd->config_lock);
2430: nbd_config_put(nbd);
2431: nbd_put(nbd);
2432: if (put_dev)
2433: nbd_put(nbd);
2434: return ret;
2435: }
SourceFile:drivers/block/nbd.c]
|
| 126/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 107418
output: 38
thoughts: 134
Thoughts: **Analyzing the NBD Configuration Vulnerability**
Okay, so I'm looking at this `nbd_genl_reconfigure` function. The first thing that jumps out is that it's checking for `netlink_capable(skb, CAP_SYS_ADMIN)`. Right, so that means this whole thing requires `CAP_SYS_ADMIN` in the initial namespace. That's a key requirement for NBD configuration. That means that an unprivileged user, by default, is *not* going to be able to trigger any kind of bug related to NBD configuration because they lack the necessary permissions. They can't just go in and change block sizes. I can't see them being able to do any concurrent modification.
But wait a minute... what about using a loop device? Could a loop device potentially be used to achieve concurrent block size changes? I need to think this through. Is there an IOCTL for changing block size on a loop device? Ah, yes! `LOOP_SET_BLOCK_SIZE`. That's the key. Now, I need to check the `loop_set_block_size` code and see if there are any obvious exploitable flaws there.
|
| 127/2 |
2026/05/31 02:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/loop.c Name:loop_set_block_size]
Results: map[SourceCode:1443: static int loop_set_block_size(struct loop_device *lo, blk_mode_t mode,
1444: struct block_device *bdev, unsigned long arg)
1445: {
1446: struct queue_limits lim;
1447: unsigned int memflags;
1448: int err = 0;
1449:
1450: /*
1451: * If we don't hold exclusive handle for the device, upgrade to it
1452: * here to avoid changing device under exclusive owner.
1453: */
1454: if (!(mode & BLK_OPEN_EXCL)) {
1455: err = bd_prepare_to_claim(bdev, loop_set_block_size, NULL);
1456: if (err)
1457: return err;
1458: }
1459:
1460: err = mutex_lock_killable(&lo->lo_mutex);
1461: if (err)
1462: goto abort_claim;
1463:
1464: if (lo->lo_state != Lo_bound) {
1465: err = -ENXIO;
1466: goto unlock;
1467: }
1468:
1469: if (lo->lo_queue->limits.logical_block_size == arg)
1470: goto unlock;
1471:
1472: sync_blockdev(lo->lo_device);
1473: invalidate_bdev(lo->lo_device);
1474:
1475: lim = queue_limits_start_update(lo->lo_queue);
1476: loop_update_limits(lo, &lim, arg);
1477:
1478: memflags = blk_mq_freeze_queue(lo->lo_queue);
1479: err = queue_limits_commit_update(lo->lo_queue, &lim);
1480: loop_update_dio(lo);
1481: blk_mq_unfreeze_queue(lo->lo_queue, memflags);
1482:
1483: unlock:
1484: mutex_unlock(&lo->lo_mutex);
1485: abort_claim:
1486: if (!(mode & BLK_OPEN_EXCL))
1487: bd_abort_claiming(bdev, loop_set_block_size);
1488: return err;
1489: }
SourceFile:drivers/block/loop.c]
|
| 128/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 108561
output: 21
thoughts: 534
Thoughts: **Analyzing Block Device Block Size Changes**
Okay, let's break this down. My initial thought was about how `loop_set_block_size` interacts with a mounted device. It calls `bd_prepare_to_claim`, and if the device is already mounted, I expect that to fail with `-EBUSY`, right? Because `mount` should exclusively claim the block device. Yep, `vfs_get_tree` confirms this. `mount` uses `blkdev_get_by_path` with `BLK_OPEN_EXCL`.
So, `loop_set_block_size` *should* fail if the device is mounted. But then I started thinking about NBD. Does `nbd_ioctl` care about `bd_prepare_to_claim`? No! It doesn't! That means `NBD_DO_IT` or `NBD_SET_BLKSIZE` *could* be called on a mounted device. But, hang on, `nbd_ioctl` requires `CAP_SYS_ADMIN` in the initial namespace. So, an unprivileged user can't exploit this via NBD.
Okay, let's consider the loop device again. What about a race condition? If `LOOP_SET_BLOCK_SIZE` is called concurrently with `mount`, `bd_prepare_to_claim` *might* succeed *before* `mount` claims the device. That would mean `loop_set_block_size` changes `logical_block_size`. Then `mount` claims the device, and now it sees the new `logical_block_size`. That's an issue! Then `IS_ALIGNED` would be true. But, the reverse is true and it shouldn't happen. If `mount` claims the device, then `loop_set_block_size` will fail with `-EBUSY`. So, a loop device *cannot* trigger this issue.
Now, I need to think bigger. Is there ANY other block device that permits changing `logical_block_size` while mounted? I need to check others. Is `cdrom` vulnerable? `floppy`? `zram`? Wait, *does* `zram` let you change the block size? I need to look into `zram_set_blocksize`.
|
| 129/2 |
2026/05/31 02:01 |
tool |
grepper |
0m
Error:
Args: map[Expression:zram_set_blocksize]
Results:
|
| 130/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 109623
output: 22
thoughts: 11
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Investigating `zram` Block Size**
Okay, first things first, I need to get a handle on the current `zram` block size. This is a crucial metric, as it directly impacts performance – especially I/O. I need to figure out the appropriate command to check that. I know the general area to look in, likely something in `/sys/block/zram*/`. Now, I'm thinking, is it optimal? Or could there be some tuning I could perform for this virtual device? Let's get the current value, and then consider it in the context of the workload. We'll be able to quickly judge its appropriateness relative to RAM and other I/O operations.
|
| 131/2 |
2026/05/31 02:01 |
tool |
grepper |
0m
Error:
Args: map[Expression:logical_block_size.*zram]
Results:
|
| 132/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 109836
output: 40
thoughts: 49
Thoughts: Okay, here's my take on those thoughts, framed as my own:
**Investigating Block Size Changes with virtio-blk**
Right, so I'm pondering `virtio-blk` here. Specifically, I'm wondering about the implications of the host changing the block size of a `virtio-blk` device *while* it's actively mounted and in use. Is that even allowed? What happens if the host reconfigures it? I know that when the host alters the configuration I can expect a call to `virtblk_config_changed`, which is probably the key point to consider. I'll need to dig into the function that gets called and figure out if it handles block size changes. I'll also check other function calls related to this scenario. There might be some interesting edge cases here related to how the guest filesystem will respond, how the existing data is impacted, and potential data corruption. It seems like the core issue revolves around whether the guest driver and filesystem are designed to handle this kind of dynamic block size shift. I'll need to analyze the implications of these changes in the code.
|
| 133/2 |
2026/05/31 02:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/virtio_blk.c Name:virtblk_config_changed]
Results: map[SourceCode: 950: static void virtblk_config_changed(struct virtio_device *vdev)
951: {
952: struct virtio_blk *vblk = vdev->priv;
953:
954: queue_work(virtblk_wq, &vblk->config_work);
955: }
SourceFile:drivers/block/virtio_blk.c]
|
| 134/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 110286
output: 40
thoughts: 12
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:
**Deep Dive into `virtblk_config_work`**
Alright, time to get into it. Let's see what's happening with `virtblk_config_work`. I need to refresh my memory and pinpoint the current state, potential bottlenecks, and any areas of concern regarding this specific component. I know it handles the configuration, so I need to check how it’s interacting with the underlying structures and the overall block device lifecycle. I'll need to dig into the function calls, the data it's processing, and how it’s synchronized with other parts of the driver. I’m thinking about any recent modifications or known issues related to configuration changes, especially during hotplug/unplug operations. Specifically, I'm focusing on ensuring it's not causing any stalls, memory leaks, or race conditions and verifying the integrity of the data it's managing. It's time to get a complete picture and confirm we're operating optimally in this section.
|
| 135/2 |
2026/05/31 02:01 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:drivers/block/virtio_blk.c Name:virtblk_config_work]
Results: map[SourceCode: SourceFile:]
|
| 136/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 110586
output: 20
thoughts: 17
Thoughts: Here's my take on the thought process, as if it were my own:
**Investigating a Potential Block Device Configuration Issue**
Alright, I need to get to the bottom of this. My gut feeling is leading me towards the configuration side of things for the virtual block device. The problem could be in how it's being set up or handled. Let's start by digging into the core function responsible for this – I'm thinking something along the lines of `virtblk_config_work_fn`, or something with a similar naming convention related to virtual block device configuration. It's the most logical place to begin my investigation, right? I'll need to examine its implementation and see what it's doing with the parameters passed to it, if there are any race conditions. Hopefully, the issue is readily apparent! If not, this will provide the groundwork for a more in-depth investigation.
|
| 137/2 |
2026/05/31 02:01 |
tool |
grepper |
0m
Args: map[Expression:config_work.*virtblk]
Results: map[Output:drivers/block/virtio_blk.c=1430=static int virtblk_probe(struct virtio_device *vdev)
--
drivers/block/virtio_blk.c-1461-
drivers/block/virtio_blk.c:1462: INIT_WORK(&vblk->config_work, virtblk_config_changed_work);
drivers/block/virtio_blk.c-1463-
]
|
| 138/2 |
2026/05/31 02:01 |
llm |
expert |
0m
Model:
Tokens:
input: 110931
output: 42
thoughts: 14
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:
**Investigating `virtblk_config_changed_work`**
Alright, time to dive into `virtblk_config_changed_work`. My initial thought is, "What's the context here?" I need to quickly refresh my understanding of how this workqueue item is triggered within the virtblk architecture. Is it tied to hotplug events, device reconfigurations, or perhaps something more nuanced like a backing store change? I need to quickly figure that out.
I need to understand its relationship to the broader virtio-blk driver. Does it interact directly with the block device layer, or does it mediate between the virtio layer and the block layer? What critical data structures does it touch, and are there potential locking concerns I should immediately flag? Are there any obvious race conditions that spring to mind based on prior experience? Are there any potential for deadlocks here?
My focus will be on identifying the *why* and the *how*. Why is this configuration change being handled asynchronously? Is it for performance reasons, or to avoid blocking critical paths? How is the workqueue item being enqueued, and what guarantees are provided regarding its execution?
Essentially, I want to construct a mental model of the control flow within this function to determine any potential problems.
|
| 139/2 |
2026/05/31 02:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/virtio_blk.c Name:virtblk_config_changed_work]
Results: map[SourceCode: 942: static void virtblk_config_changed_work(struct work_struct *work)
943: {
944: struct virtio_blk *vblk =
945: container_of(work, struct virtio_blk, config_work);
946:
947: virtblk_update_capacity(vblk, true);
948: }
SourceFile:drivers/block/virtio_blk.c]
|
| 140/2 |
2026/05/31 02:01 |
llm |
expert |
1m
Model:
Tokens:
input: 111410
output: 37
thoughts: 120
Thoughts: **Capacity Updates: A Quick Look**
Okay, so `virtblk_update_capacity` is pretty straightforward – it’s just dealing with capacity updates. But, a nagging question keeps popping up. What about NVMe? Can NVMe namespaces even change their block size dynamically? It's a key detail to consider. I know NVMe namespaces *can* be reformatted using "Format NVM", but that requires exclusive access—meaning the namespace has to be unmounted first.
Now, let's step back from NVMe for a second. What if we're dealing with something more… flexible, like a USB mass storage device? Could a USB device potentially change its block size on the fly? Hmm, USB mass storage devices report block size in `READ CAPACITY`, and if it changes, the kernel *should* update it. I need to make sure this is actually happening. Time to dive into the code. I'll take a quick look at `sd_read_capacity` and see how it handles this potential block size change. I want to make sure we are not missing a crucial update path here.
|
| 141/2 |
2026/05/31 02:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/scsi/sd.c Name:sd_read_capacity]
Results: map[SourceCode:2814: /*
2815: * read disk capacity
2816: */
2817: static void
2818: sd_read_capacity(struct scsi_disk *sdkp, struct queue_limits *lim,
2819: unsigned char *buffer)
2820: {
2821: int sector_size;
2822: struct scsi_device *sdp = sdkp->device;
2823:
2824: if (sd_try_rc16_first(sdp)) {
2825: sector_size = read_capacity_16(sdkp, sdp, lim, buffer);
2826: if (sector_size == -EOVERFLOW)
2827: goto got_data;
2828: if (sector_size == -ENODEV)
2829: return;
2830: if (sector_size < 0)
2831: sector_size = read_capacity_10(sdkp, sdp, buffer);
2832: if (sector_size < 0)
2833: return;
2834: } else {
2835: sector_size = read_capacity_10(sdkp, sdp, buffer);
2836: if (sector_size == -EOVERFLOW)
2837: goto got_data;
2838: if (sector_size < 0)
2839: return;
2840: if ((sizeof(sdkp->capacity) > 4) &&
2841: (sdkp->capacity > 0xffffffffULL)) {
2842: int old_sector_size = sector_size;
2843: sd_printk(KERN_NOTICE, sdkp, "Very big device. "
2844: "Trying to use READ CAPACITY(16).\n");
2845: sector_size = read_capacity_16(sdkp, sdp, lim, buffer);
2846: if (sector_size < 0) {
2847: sd_printk(KERN_NOTICE, sdkp,
2848: "Using 0xffffffff as device size\n");
2849: sdkp->capacity = 1 + (sector_t) 0xffffffff;
2850: sector_size = old_sector_size;
2851: goto got_data;
2852: }
2853: /* Remember that READ CAPACITY(16) succeeded */
2854: sdp->try_rc_10_first = 0;
2855: }
2856: }
2857:
2858: /* Some devices are known to return the total number of blocks,
2859: * not the highest block number. Some devices have versions
2860: * which do this and others which do not. Some devices we might
2861: * suspect of doing this but we don't know for certain.
2862: *
2863: * If we know the reported capacity is wrong, decrement it. If
2864: * we can only guess, then assume the number of blocks is even
2865: * (usually true but not always) and err on the side of lowering
2866: * the capacity.
2867: */
2868: if (sdp->fix_capacity ||
2869: (sdp->guess_capacity && (sdkp->capacity & 0x01))) {
2870: sd_printk(KERN_INFO, sdkp, "Adjusting the sector count "
2871: "from its reported value: %llu\n",
2872: (unsigned long long) sdkp->capacity);
2873: --sdkp->capacity;
2874: }
2875:
2876: got_data:
2877: if (sector_size == 0) {
2878: sector_size = 512;
2879: sd_printk(KERN_NOTICE, sdkp, "Sector size 0 reported, "
2880: "assuming 512.\n");
2881: }
2882:
2883: if (sector_size != 512 &&
2884: sector_size != 1024 &&
2885: sector_size != 2048 &&
2886: sector_size != 4096) {
2887: sd_printk(KERN_NOTICE, sdkp, "Unsupported sector size %d.\n",
2888: sector_size);
2889: /*
2890: * The user might want to re-format the drive with
2891: * a supported sectorsize. Once this happens, it
2892: * would be relatively trivial to set the thing up.
2893: * For this reason, we leave the thing in the table.
2894: */
2895: sdkp->capacity = 0;
2896: /*
2897: * set a bogus sector size so the normal read/write
2898: * logic in the block layer will eventually refuse any
2899: * request on this device without tripping over power
2900: * of two sector size assumptions
2901: */
2902: sector_size = 512;
2903: }
2904: lim->logical_block_size = sector_size;
2905: lim->physical_block_size = sdkp->physical_block_size;
2906: sdkp->device->sector_size = sector_size;
2907:
2908: if (sdkp->capacity > 0xffffffff)
2909: sdp->use_16_for_rw = 1;
2910:
2911: }
SourceFile:drivers/scsi/sd.c]
|
| 142/2 |
2026/05/31 02:02 |
llm |
expert |
0m
Model:
Tokens:
input: 113392
output: 38
thoughts: 47
Thoughts: Okay, here's my interpretation of this technical snippet, expressed as if it's my own thought process:
**Logical Block Size Assignment in SD Card Initialization**
Right, so `sd_read_capacity`... it's immediately setting `lim->logical_block_size` equal to `sector_size`. Okay, that makes sense. We're directly mapping the logical block size to the physical sector size retrieved from the SD card. Standard, fundamental stuff for block device setup.
The interesting question is always *when* is this function called? I need to be aware of the context. Let me trace back... Aha! It's called from `sd_revalidate_disk`. Got it. So, disk validation and re-validation, which I'd assume includes things like detecting changes in the media, checking the reported capacity, all the preliminary checks. That's the trigger for this logical block size assignment. Excellent. This means this critical block size configuration is tightly bound to re-validation events, so it’s likely updated when the card is re-mounted, or when the system detects a change or some sort of refresh is needed. It’s the mechanism to reflect new sector size values, after a card has been swapped or changed in any way.
|
| 143/2 |
2026/05/31 02:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/scsi/sd.c Name:sd_revalidate_disk]
Results: map[SourceCode:3689: /**
3690: * sd_revalidate_disk - called the first time a new disk is seen,
3691: * performs disk spin up, read_capacity, etc.
3692: * @disk: struct gendisk we care about
3693: **/
3694: static int sd_revalidate_disk(struct gendisk *disk)
3695: {
3696: struct scsi_disk *sdkp = scsi_disk(disk);
3697: struct scsi_device *sdp = sdkp->device;
3698: sector_t old_capacity = sdkp->capacity;
3699: struct queue_limits lim;
3700: unsigned char *buffer;
3701: unsigned int dev_max;
3702: int err;
3703:
3704: SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp,
3705: "sd_revalidate_disk\n"));
3706:
3707: /*
3708: * If the device is offline, don't try and read capacity or any
3709: * of the other niceties.
3710: */
3711: if (!scsi_device_online(sdp))
3712: goto out;
3713:
3714: buffer = kmalloc(SD_BUF_SIZE, GFP_KERNEL);
3715: if (!buffer) {
3716: sd_printk(KERN_WARNING, sdkp, "sd_revalidate_disk: Memory "
3717: "allocation failure.\n");
3718: goto out;
3719: }
3720:
3721: sd_spinup_disk(sdkp);
3722:
3723: lim = queue_limits_start_update(sdkp->disk->queue);
3724:
3725: /*
3726: * Without media there is no reason to ask; moreover, some devices
3727: * react badly if we do.
3728: */
3729: if (sdkp->media_present) {
3730: sd_read_capacity(sdkp, &lim, buffer);
3731: /*
3732: * Some USB/UAS devices return generic values for mode pages
3733: * until the media has been accessed. Trigger a READ operation
3734: * to force the device to populate mode pages.
3735: */
3736: if (sdp->read_before_ms)
3737: sd_read_block_zero(sdkp);
3738: /*
3739: * set the default to rotational. All non-rotational devices
3740: * support the block characteristics VPD page, which will
3741: * cause this to be updated correctly and any device which
3742: * doesn't support it should be treated as rotational.
3743: */
3744: lim.features |= (BLK_FEAT_ROTATIONAL | BLK_FEAT_ADD_RANDOM);
3745:
3746: if (scsi_device_supports_vpd(sdp)) {
3747: sd_read_block_provisioning(sdkp);
3748: sd_read_block_limits(sdkp, &lim);
3749: sd_read_block_limits_ext(sdkp);
3750: sd_read_block_characteristics(sdkp, &lim);
3751: sd_zbc_read_zones(sdkp, &lim, buffer);
3752: }
3753:
3754: sd_config_discard(sdkp, &lim, sd_discard_mode(sdkp));
3755:
3756: sd_print_capacity(sdkp, old_capacity);
3757:
3758: sd_read_write_protect_flag(sdkp, buffer);
3759: sd_read_cache_type(sdkp, buffer);
3760: sd_read_io_hints(sdkp, buffer);
3761: sd_read_app_tag_own(sdkp, buffer);
3762: sd_read_write_same(sdkp, buffer);
3763: sd_read_security(sdkp, buffer);
3764: sd_config_protection(sdkp, &lim);
3765: }
3766:
3767: /*
3768: * We now have all cache related info, determine how we deal
3769: * with flush requests.
3770: */
3771: sd_set_flush_flag(sdkp, &lim);
3772:
3773: /* Initial block count limit based on CDB TRANSFER LENGTH field size. */
3774: dev_max = sdp->use_16_for_rw ? SD_MAX_XFER_BLOCKS : SD_DEF_XFER_BLOCKS;
3775:
3776: /* Some devices report a maximum block count for READ/WRITE requests. */
3777: dev_max = min_not_zero(dev_max, sdkp->max_xfer_blocks);
3778: lim.max_dev_sectors = logical_to_sectors(sdp, dev_max);
3779:
3780: if (sd_validate_min_xfer_size(sdkp))
3781: lim.io_min = logical_to_bytes(sdp, sdkp->min_xfer_blocks);
3782: else
3783: lim.io_min = 0;
3784:
3785: /*
3786: * Limit default to SCSI host optimal sector limit if set. There may be
3787: * an impact on performance for when the size of a request exceeds this
3788: * host limit.
3789: */
3790: lim.io_opt = sdp->host->opt_sectors << SECTOR_SHIFT;
3791: if (sd_validate_opt_xfer_size(sdkp, dev_max)) {
3792: lim.io_opt = min_not_zero(lim.io_opt,
3793: logical_to_bytes(sdp, sdkp->opt_xfer_blocks));
3794: }
3795:
3796: sdkp->first_scan = 0;
3797:
3798: set_capacity_and_notify(disk, logical_to_sectors(sdp, sdkp->capacity));
3799: sd_config_write_same(sdkp, &lim);
3800: kfree(buffer);
3801:
3802: err = queue_limits_commit_update_frozen(sdkp->disk->queue, &lim);
3803: if (err)
3804: return err;
3805:
3806: /*
3807: * Query concurrent positioning ranges after
3808: * queue_limits_commit_update() unlocked q->limits_lock to avoid
3809: * deadlock with q->sysfs_dir_lock and q->sysfs_lock.
3810: */
3811: if (sdkp->media_present && scsi_device_supports_vpd(sdp))
3812: sd_read_cpr(sdkp);
3813:
3814: /*
3815: * For a zoned drive, revalidating the zones can be done only once
3816: * the gendisk capacity is set. So if this fails, set back the gendisk
3817: * capacity to 0.
3818: */
3819: if (sd_zbc_revalidate_zones(sdkp))
3820: set_capacity_and_notify(disk, 0);
3821:
3822: out:
3823: return 0;
3824: }
SourceFile:drivers/scsi/sd.c]
|
| 144/2 |
2026/05/31 02:02 |
llm |
expert |
0m
Model:
Tokens:
input: 115934
output: 36
thoughts: 413
Thoughts: **Analyzing a Disk Revalidation Bug**
Okay, so `sd_revalidate_disk` is calling `queue_limits_commit_update_frozen`, which immediately triggers some flags. I see that this happens when a USB mass storage device's capacity or block size is altered. That makes sense, but the critical question is: can `sd_revalidate_disk` be called while the device is mounted? Yes, potentially, if the media changes (like swapping a CD-ROM) or if a revalidation is explicitly triggered.
Ah, but if it *is* mounted, `queue_limits_commit_update_frozen` freezes the queue, updates the limits, and unfreezes it. That means the `logical_block_size` *can* actually change while the filesystem is actively in use! That's a huge potential issue.
Now, if the `logical_block_size` shifts, say from 512 to 1024 bytes while mounted, that critical alignment check, `IS_ALIGNED(sb->s_blocksize, bdev_logical_block_size(bdev))`, could suddenly become FALSE. That's *exactly* what triggers the warning!
So, the crux of the vulnerability is a block size change mid-mount. That means a malicious USB device could trigger this. That's a pretty frightening Peripheral Trigger! Or, someone could manipulate an NBD server if they have `CAP_SYS_ADMIN` rights, which is far less alarming.
Wait, didn't that bug report specify that syzkaller was the trigger, using NBD? And syzkaller runs as root (`UID: 0`) and therefore has `CAP_SYS_ADMIN`? Bingo. It's using NBD. So they're able to configure it.
So, the real question is, can an unprivileged user trigger this somehow? The answer, at least straightforwardly, is no, because configuring NBD needs `CAP_SYS_ADMIN`. Similarly, mounting a filesystem also requires `CAP_SYS_ADMIN` within the user namespace.
But, hang on... what about user namespaces? If an unprivileged user creates a user namespace, they have `CAP_SYS_ADMIN` *within that namespace*. This could be a vector. But, and this is crucial, `nbd_ioctl` uses `capable(CAP_SYS_ADMIN)` and *not* `ns_capable(..., CAP_SYS_ADMIN)`! That means the namespace trick won't work in this case. Looks like someone needs to verify that `capable` test. Good.
|
| 145/2 |
2026/05/31 02:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/nbd.c Name:nbd_ioctl]
Results: map[SourceCode:1629: static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
1630: unsigned int cmd, unsigned long arg)
1631: {
1632: struct nbd_device *nbd = bdev->bd_disk->private_data;
1633: struct nbd_config *config = nbd->config;
1634: int error = -EINVAL;
1635:
1636: if (!capable(CAP_SYS_ADMIN))
1637: return -EPERM;
1638:
1639: /* The block layer will pass back some non-nbd ioctls in case we have
1640: * special handling for them, but we don't so just return an error.
1641: */
1642: if (_IOC_TYPE(cmd) != 0xab)
1643: return -EINVAL;
1644:
1645: mutex_lock(&nbd->config_lock);
1646:
1647: /* Don't allow ioctl operations on a nbd device that was created with
1648: * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
1649: */
1650: if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
1651: (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
1652: error = __nbd_ioctl(bdev, nbd, cmd, arg);
1653: else
1654: dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
1655: mutex_unlock(&nbd->config_lock);
1656: return error;
1657: }
SourceFile:drivers/block/nbd.c]
|
| 146/2 |
2026/05/31 02:03 |
llm |
expert |
0m
Model:
Tokens:
input: 117463
output: 34
thoughts: 1289
Thoughts: **Analyzing a Potential Block Size Issue in the Linux Kernel**
Okay, let's break this down systematically. I'm focusing on a potential vulnerability related to block size changes, specifically within the kernel. The goal is to determine if it's exploitable, a denial-of-service risk, and who can trigger it.
First, I'm checking if an unprivileged user can leverage `CAP_SYS_ADMIN` in the initial user namespace to configure Network Block Device (NBD). The answer is no, this is not possible. What about loop devices? The problem with loop devices is that they cannot change block size while mounted. USB devices are also a potential area, but a malicious USB device can revalidate and change its block size, and unprivileged users cannot plug in a USB. So this is a Peripheral Trigger. Can an unprivileged user trigger a revalidate of a CD-ROM? It's the same situation as USB, requiring physical access. The `loop_set_status` and `loop_configure` functions are not vulnerable, as they can't change the block size either.
My main concern is whether an unprivileged user can, in any way, trigger this warning. The answer seems to be no because they cannot change the logical block size of a mounted device.
So, let's categorize this issue. It is not exploitable in the traditional sense, as it returns NULL, which is handled by callers. It's also not a denial-of-service issue because it's a `WARN_ON_ONCE` and doesn't crash the kernel (unless `panic_on_warn` is set). It just fails the mount or read. There is no possibility to access it from unprivileged processes or user namespaces. A VM guest isn't likely to trigger it unless the VM host changes the block size. I've to think about this a bit more.
The next question is whether a VM Host can trigger this in a VM Guest. It seems yes, because the host can change the block size of a virtio-blk device while the guest has it mounted, which will trigger the warning in the guest. This means I need to consider a potential VM Host Trigger in the confidential computing context. The answer is yes, because the host can modify the block size.
This eliminates any ethernet or remote triggers. The only triggers appear to be peripheral and a VM host. Malicious Filesystem Trigger: No, it is not possible because the block device itself is the cause.
Now, I'm going to look at one final test case to double-check `udf_fill_super`. This is a hypothetical scenario where `bdev_logical_block_size` is 1024, the block size is also 1024, `udf_load_vrs` fails, and then the block size is doubled to 2048. It looks like it calls `sb_bread` which calls `__bread_gfp`. Here, `__getblk_slow` checks if the block size is aligned with the logical block size. This is true because 2048 is aligned with 1024.
Then, I'm going to check the second case, when `bdev_logical_block_size` is 2048 and `sb->s_blocksize` is 1024. How could this happen? If the user passes `bs=1024` on mount and `uopt->flags & (1 << UDF_FLAG_BLOCKSIZE_SET)` is true. If the user passes `bs=1024`, `uopt->blocksize` is 1024. Then, the block size is set to 1024, `udf_load_vrs` is called. So, the bug is still possible when the user sets the block size to a smaller value.
|
| 147/2 |
2026/05/31 02:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bdev.c Name:set_blocksize]
Results: map[SourceCode: 178: int set_blocksize(struct file *file, int size)
179: {
180: struct inode *inode = file->f_mapping->host;
181: struct block_device *bdev = I_BDEV(inode);
182: int ret;
183:
184: ret = bdev_validate_blocksize(bdev, size);
185: if (ret)
186: return ret;
187:
188: if (!file->private_data)
189: return -EINVAL;
190:
191: /* Don't change the size if it is same as current */
192: if (inode->i_blkbits != blksize_bits(size)) {
193: /*
194: * Flush and truncate the pagecache before we reconfigure the
195: * mapping geometry because folio sizes are variable now. If a
196: * reader has already allocated a folio whose size is smaller
197: * than the new min_order but invokes readahead after the new
198: * min_order becomes visible, readahead will think there are
199: * "zero" blocks per folio and crash. Take the inode and
200: * invalidation locks to avoid racing with
201: * read/write/fallocate.
202: */
203: inode_lock(inode);
204: filemap_invalidate_lock(inode->i_mapping);
205:
206: sync_blockdev(bdev);
207: kill_bdev(bdev);
208:
209: inode->i_blkbits = blksize_bits(size);
210: mapping_set_folio_min_order(inode->i_mapping, get_order(size));
211: kill_bdev(bdev);
212: filemap_invalidate_unlock(inode->i_mapping);
213: inode_unlock(inode);
214: }
215: return 0;
216: }
SourceFile:block/bdev.c]
|
| 148/2 |
2026/05/31 02:03 |
llm |
expert |
0m
Model:
Tokens:
input: 120230
output: 40
thoughts: 5532
Thoughts: **Analyzing the UDF Filesystem Mount with NBD and Block Size Alignment Issues**
Okay, so I've been tracing through this UDF filesystem mounting process, specifically looking at how the block size gets handled, especially when Network Block Devices (NBD) are involved. It starts with the `set_blocksize` function and a call to `bdev_validate_blocksize`. This is where it starts to get interesting. The core check is to see if the requested block size is smaller than the device's logical block size. If it is, boom, `-EINVAL` and everything goes south. I initially thought if the mount's blocksize (`bs=1024`) was smaller than the device's (`bdev_logical_block_size` is 2048), `set_blocksize` would return `-EINVAL`, but that's not exactly the case.
I was seeing an `-EINVAL` error eventually propagating all the way up to `udf_fill_super`. This meant that `sb->s_blocksize` was not correctly aligned with the underlying device. So, the system was reporting `sb->s_blocksize` CANNOT be smaller than the `bdev_logical_block_size(bdev)`! So, `IS_ALIGNED(sb->s_blocksize, bdev_logical_block_size(bdev))` MUST be TRUE.
I started to dig deeper, specifically looking at the call trace from `sb_bread`. It looked like `sb_bread` eventually calls `__bread_gfp`, passing `sb->s_bdev`, `block`, and `sb->s_blocksize`. So the block size value comes directly from `sb->s_blocksize`. And it’s set using `sb_set_blocksize`. `sb_set_blocksize` *should* be ensuring that `sb->s_blocksize >= bdev_logical_block_size(bdev)`, and that the block size is a power of 2. So if `sb->s_blocksize` is a multiple of `bdev_logical_block_size(bdev)`, the `IS_ALIGNED` check should *always* be true. The only way to cause a misalignment is if `bdev_logical_block_size(bdev)` increases *after* the `sb_set_blocksize` has been called!
I was seeing that `NBD_DO_IT` could potentially increase it. So, I figured the key to the problem must be a race condition. If `NBD_DO_IT` could be running at the same time as the `mount` process, it could increase the device block size after the filesystem had selected a blocksize. I thought it was very strange because the reproduction was single-threaded. Then, I realized that `NBD_DO_IT` uses `wait_event_interruptible`, and it can return immediately if interrupted by a signal. But, is there something that is running concurrently? `recv_work` might be still running when a signal interrupts the thread! I checked, but `nbd_set_size` is called BEFORE the `wait_event_interruptible`, so the block size has already been set, and `logical_block_size` is 1024, when `NBD_DO_IT` returns. So when `mount` runs the first time, `uopt->blocksize` would already be set to 1024. Then, `IS_ALIGNED(1024, 1024)` is TRUE.
Then I realized that `NBD_DO_IT` could fail before `nbd_set_size`. If it fails before `nbd_set_size`, `logical_block_size` is 512, because no block size change happens. So the block size will be set to `512`, and so `IS_ALIGNED(512, 512)` is TRUE, so it still works.
I realized that `NBD_DO_IT` could set `logical_block_size` to 1024, and returns, then `mount` is called. So `udf_fill_super` sets `uopt->blocksize = 1024`. Then `sb_set_blocksize(sb, 1024)` is called. Everything is still fine because `IS_ALIGNED(1024, 1024)` is TRUE. Then `udf_load_vrs` is called and fails, and it doubles `uopt->blocksize` to 2048, and `sb_set_blocksize(sb, 2048)` is called. Then
|
| 149/2 |
2026/05/31 02:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/virtio_blk.c Name:virtblk_update_capacity]
Results: map[SourceCode: 911: /* The queue's logical block size must be set before calling this */
912: static void virtblk_update_capacity(struct virtio_blk *vblk, bool resize)
913: {
914: struct virtio_device *vdev = vblk->vdev;
915: struct request_queue *q = vblk->disk->queue;
916: char cap_str_2[10], cap_str_10[10];
917: unsigned long long nblocks;
918: u64 capacity;
919:
920: /* Host must always specify the capacity. */
921: virtio_cread(vdev, struct virtio_blk_config, capacity, &capacity);
922:
923: nblocks = DIV_ROUND_UP_ULL(capacity, queue_logical_block_size(q) >> 9);
924:
925: string_get_size(nblocks, queue_logical_block_size(q),
926: STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
927: string_get_size(nblocks, queue_logical_block_size(q),
928: STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));
929:
930: dev_notice(&vdev->dev,
931: "[%s] %s%llu %d-byte logical blocks (%s/%s)\n",
932: vblk->disk->disk_name,
933: resize ? "new size: " : "",
934: nblocks,
935: queue_logical_block_size(q),
936: cap_str_10,
937: cap_str_2);
938:
939: set_capacity_and_notify(vblk->disk, capacity);
940: }
SourceFile:drivers/block/virtio_blk.c]
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| 150/2 |
2026/05/31 02:03 |
llm |
expert |
0m
Model:
Tokens:
input: 127406
output: 66
thoughts: 1388
Thoughts: **Analysis of Block Device Logical Block Size Modification**
Okay, let's break this down systematically. My initial thought was centered on how block size changes impact mounted filesystems and potential vulnerabilities.
* `virtblk_update_capacity` is out; it only deals with capacity changes, *not* logical block size. `virtblk_probe` is where the block size is initially set, and that's it. So, a virtio-blk device can't be used to trigger this after initialization.
* Now, USB mass storage... `sd_revalidate_disk` is the key function. It's called on media changes. A USB device simulating a media change *could* change the block size. But if it truly simulates a *media* change, the device would be invalidated, and `mount` would fail anyway. Okay, what if the mount is running *concurrently* with `sd_revalidate_disk`? That's the edge case. Peripheral Trigger: Yes, that's possible.
* Checked `NBD_DO_IT`... requires `CAP_SYS_ADMIN`. Not accessible to unprivileged users. Moving on.
* Loop devices? `loop_set_block_size` calls `bd_prepare_to_claim`. If `mount` has already claimed the block device, `bd_prepare_to_claim` will fail. So, loop devices *cannot* trigger this concurrently.
* Then I thought about NBD and it hits me! `NBD_DO_IT` doesn't check if the device is claimed! NBD *allows* changing the block size while the device is mounted! So NBD is the culprit. That's a lack of mutual exclusion in NBD. However, NBD *requires* `CAP_SYS_ADMIN`, so not a security hole for unprivileged users.
* What about `sd_revalidate_disk`? Does it check if the device is claimed? It is called from `sd_check_events` and, if the device reports `DISK_EVENT_MEDIA_CHANGE`, the block layer calls `disk_force_media_change`, which invalidates the device. But it can also be triggered by `BLKDEV_REREAD_PART`, which *also* requires `CAP_SYS_ADMIN`. Still...if a USB device *lies* and says "media changed", `sd_revalidate_disk` is called! `sd_revalidate_disk` *can* run concurrently with `mount` even if the device is claimed. So a malicious USB device *can* trigger this warning. But it's just a warning.
* Now, let's summarize:
* Exploitable: No
* Denial Of Service: No
* Accessible From Unprivileged Processes: No
* Accessible From User Namespaces: No
* VM Guest Trigger: No
* VM Host Trigger in The Confidential Computing Context: No (virtio-blk doesn't support changing block size after probe)
* Ethernet Network Trigger: No
* Other Remote Trigger: No
* Peripheral Trigger: Yes (USB mass storage can change block size during revalidate)
* Malicious Filesystem Trigger: No
* Wait, remote NBD? The server can't dictate the block size; the *client* (using `ioctl`) does. That means a remote NBD server cannot directly trigger this without the local root user running the NBD client. So, Ethernet Network Trigger: No.
* Confirmed `virtblk_update_capacity` doesn't touch block size. Confirmed. `virtblk_probe` reads the block size, and that's the end of it.
* Confirmed `sd_revalidate_disk` can change it. `sd_read_capacity` sets it, then `queue_limits_commit_update_frozen` updates the queue limits. A USB device *can* do this.
* Finally, the `WARN_ON_ONCE` isn't a DoS, it just prints a warning, and returns null. The caller handles the NULL gracefully.
I have reached the final conclusion.
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| 151/2 |
2026/05/31 02:04 |
tool |
set-results |
0m
Args: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
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| 152/2 |
2026/05/31 02:04 |
llm |
expert |
0m
Model:
Tokens:
input: 129828
output: 783
thoughts: 304
Thoughts: **Final Response: Bug Analysis Complete**
Okay, the analysis is done, and it's time to craft the final response. Here's what I've got: that pesky `WARN_ON_ONCE` triggered in `__getblk_slow`? I've nailed down the root cause. It's all about block size misalignment. Specifically, when the logical block size of a block device gets modified *concurrently* while the filesystem is mounting.
The syzkaller reproducer nails this by simultaneously running `NBD_DO_IT`, forcing the NBD logical block size to 1024, *and* `mount`, which grabs an initial logical block size of 512, and assumes 512 for later block access. However, because `NBD_DO_IT` needs `CAP_SYS_ADMIN` in the initial user namespace, unprivileged users can't trigger this specific scenario.
Thinking more broadly, this isn't *just* an NBD issue. While loop devices are safe because they prevent block size changes when mounted, a malicious USB mass storage device could pull a fast one. It could simulate a media change, tweak its reported block size *during* the revalidation process, while being mounted, and boom, same warning. The device is reporting a new block size mid-mount, and `__getblk_slow` gets confused.
The good news? It's not a complete disaster. It's just a kernel warning (`WARN_ON_ONCE`), and the mount operation gracefully fails because `__getblk_slow` returns `NULL`, which the UDF code handles properly. No memory corruption, no system crash, assuming `panic_on_warn=0` is the default. Still, the warning is a sign that something is amiss, and needs to be addressed.
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| 153/1 |
2026/05/31 02:04 |
action |
format-explanation |
0m
Results: map[Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the vulnerability:
**Root Cause Analysis:**
The warning `WARN_ON_ONCE(!IS_ALIGNED(size, bdev_logical_block_size(bdev)))` in
`__getblk_slow()` is triggered when a filesystem attempts to read a block using
a size that is not aligned to the underlying block device's logical block size.
In the provided syzkaller reproducer, this is caused by a data race involving
the Network Block Device (NBD). The reproducer concurrently executes an NBD
ioctl (`NBD_DO_IT`) and a `mount` system call for the UDF filesystem on the same
NBD device.
1. Initially, the NBD device has a default logical block size of 512 bytes.
2. The `mount` system call starts and `udf_fill_super()` initializes its block
size to the device's current logical block size (512 bytes).
3. Concurrently, the `NBD_DO_IT` ioctl executes `nbd_start_device()`, which
synchronously updates the device's logical block size to 1024 bytes (the default
NBD block size).
4. When the UDF filesystem proceeds to read the Volume Recognition Sequence
(VRS) via `sb_bread()`, it requests a 512-byte block.
5. `__getblk_slow()` checks if the requested size (512) is aligned to the *new*
logical block size (1024). Since it is not, the warning is triggered.
**Security Impact:**
- **Exploitable:** No. The `WARN_ON_ONCE` simply prints a warning to the kernel
log and returns `NULL`. The UDF filesystem code (`udf_read_tagged`,
`udf_check_anchor_block`, etc.) properly handles the `NULL` return value from
the buffer cache and fails gracefully. There is no memory corruption,
out-of-bounds access, or use-after-free.
- **Denial of Service:** No. In production builds (where `panic_on_warn` is
disabled), the kernel will not crash or hang. The mount operation will simply
fail.
- **Unprivileged / User Namespace Access:** No. The NBD ioctls (`NBD_DO_IT`,
`NBD_SET_BLKSIZE`, etc.) strictly require `CAP_SYS_ADMIN` in the initial user
namespace (`capable(CAP_SYS_ADMIN)`). Unprivileged users or users within a user
namespace cannot configure NBD devices to trigger this race. Other software
block devices like `loop` safely prevent block size changes while the device is
exclusively claimed (mounted) via `bd_prepare_to_claim()`.
- **Peripheral Trigger:** Yes. A malicious USB mass storage device could
theoretically trigger this by simulating a media change and altering its
reported sector size in its `READ CAPACITY` response while the kernel is
concurrently probing/mounting it (via `sd_revalidate_disk` updating the queue
limits). However, the impact remains limited to a harmless warning.
- **VM Host/Guest Trigger:** No. Virtio block devices (`virtio-blk`) read their
block size during the initial probe and do not support the host dynamically
changing the logical block size afterward (`virtblk_update_capacity` only
updates the total capacity, not the block size).
**Conclusion:**
This is a harmless race condition resulting in a kernel warning. It requires
root privileges to trigger via NBD and does not pose a security risk (no memory
corruption, privilege escalation, or denial of service).]
|