| 0/0 |
2026/08/22 14:48 |
flow |
assessment-security |
32m
Results: map[DenialOfService:true Explanation:The bug is a memory leak caused by a circular reference when mapping the
`/dev/iommu` file descriptor itself into an `ioas` object using the
`IOMMU_IOAS_MAP_FILE` ioctl.
When `IOMMU_IOAS_MAP_FILE` is called with the file descriptor of `/dev/iommu`,
the kernel calls `iopt_alloc_file_pages()`, which takes a reference to the
`file` struct (`pages->file = get_file(file)`). This `pages` object is then
attached to the `ioas` object's page table (`iopt`).
However, the `ioas` object itself is owned by the `iommufd_ctx`, which is tied
to the `/dev/iommu` file descriptor. This creates a reference cycle:
`file (/dev/iommu)` -> `iommufd_ctx` -> `ioas` -> `iopt_area` -> `iopt_pages` ->
`file (/dev/iommu)`.
When the user process exits or closes the file descriptor, the `file`'s
reference count is decremented but does not reach zero because of the reference
held by `iopt_pages`. As a result, the `iommufd_fops_release()` function is
never called, and the `ioas` object is never destroyed, leading to a permanent
memory leak of the `file`, `iommufd_ctx`, `ioas`, and associated page table
structures.
**Exploitability:**
This is a pure memory leak (resource exhaustion) and does not lead to memory
corruption, use-after-free, or information leaks. It is not exploitable for
privilege escalation.
**Denial of Service:**
An attacker with access to `/dev/iommu` can repeatedly trigger this bug in a
loop to leak kernel memory, eventually causing the system to run out of memory
(OOM) and crash, leading to a Denial of Service.
**Access Restrictions:**
The `/dev/iommu` device node is typically created with `0660` permissions and is
owned by `root:root` (or a specific group like `kvm`). Therefore, it is not
accessible to a typical unprivileged user or from within a user namespace unless
the user has been explicitly granted access to the device node. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/08/22 14:48 |
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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*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=*/0x1000, /*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)) {}
// socket$inet6_tcp arguments: [
// domain: const = 0xa (8 bytes)
// type: const = 0x1 (8 bytes)
// proto: const = 0x0 (4 bytes)
// ]
// returns sock_tcp6
syscall(__NR_socket, /*domain=*/0xaul, /*type=*/1ul, /*proto=*/0);
// openat$iommufd arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 69 6f 6d 6d 75 00} (length 0xb)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd_iommufd
memcpy((void*)0x200000000000, "/dev/iommu\000", 11);
res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000000000ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$IOMMU_IOAS_ALLOC arguments: [
// fd: fd_iommufd (resource)
// cmd: const = 0x3b81 (4 bytes)
// arg: ptr[in, iommu_ioas_alloc] {
// iommu_ioas_alloc {
// size: len = 0xc (4 bytes)
// flags: const = 0x0 (4 bytes)
// out_ioas_id: ioas_handle (resource)
// }
// }
// ]
*(uint32_t*)0x200000000040 = 0xc;
*(uint32_t*)0x200000000044 = 0;
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x3b81, /*arg=*/0x200000000040ul);
// ioctl arguments: [
// fd: fd (resource)
// cmd: int32 = 0x3b8f (4 bytes)
// arg: ptr[in, buffer] {
// buffer: {28 00 00 00 06 00 00 00 01 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 00 10} (length 0x1a)
// }
// ]
memcpy((void*)0x2000000000c0, "\x28\x00\x00\x00\x06\x00\x00\x00\x01\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10", 26);
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x3b8f, /*arg=*/0x2000000000c0ul);
return 0;
}
]
|
| 2/1 |
2026/08/22 14:48 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/b91c7dc3c2f9eea7d2724bdd80cfba2fb90652f5]
|
| 3/1 |
2026/08/22 14:50 |
action |
kernel-builder |
14m
Results: map[KernelObj:/app/workdir/cache/build/a547ec0fc3aed7bec94db6cb3e2790c048c8833b]
|
| 4/1 |
2026/08/22 15:04 |
action |
codesearch-prepare |
11m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/08/22 15:15 |
agent |
expert |
5m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false 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, elevated privileges, or an information leak.
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.
Information leaks are exploitable on their own and should be classified as such. A bug that copies kernel
memory contents to userspace (e.g. an out-of-bounds read whose result is returned to the caller, or
uninitialized stack/heap bytes written to a user buffer) is exploitable: it can reveal kernel pointer
values and defeat KASLR, expose sensitive data such as cryptographic keys or other processes' memory, and
serves as a necessary building block in most modern kernel privilege-escalation exploit chains. Do not classify
an information leak as non-exploitable solely because it does not directly cause a memory write or control-flow
hijack; the leak itself is the exploit primitive.
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:
2026/08/22 14:47:52 executed programs: 26
2026/08/22 14:47:59 executed programs: 40
2026/08/22 14:48:07 executed programs: 54
2026/08/22 14:48:14 executed programs: 68
BUG: memory leak
unreferenced object 0xffff88812811f9c0 (size 176):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
00 00 00 00 19 00 08 04 40 fc a8 85 ff ff ff ff ........@.......
00 02 38 03 81 88 ff ff 80 cd 61 11 81 88 ff ff ..8.......a.....
backtrace (crc 1214ee3a):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
kmem_cache_alloc_noprof+0x352/0x440 mm/slub.c:4933
alloc_empty_file+0x57/0x180 fs/file_table.c:262
path_openat+0x44/0x11f0 fs/namei.c:4986
do_file_open+0x121/0x200 fs/namei.c:5029
do_sys_openat2+0xa7/0x150 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x82/0xf0 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff8881280ec188 (size 56):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
ff ff 01 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 2672a0c6):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
kmem_cache_alloc_noprof+0x352/0x440 mm/slub.c:4933
lsm_file_alloc security/security.c:171 [inline]
security_file_alloc+0x30/0x250 security/security.c:2406
init_file+0x3e/0x160 fs/file_table.c:184
alloc_empty_file+0x75/0x180 fs/file_table.c:266
path_openat+0x44/0x11f0 fs/namei.c:4986
do_file_open+0x121/0x200 fs/namei.c:5029
do_sys_openat2+0xa7/0x150 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x82/0xf0 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff88811161cd80 (size 192):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
c0 f9 11 28 81 88 ff ff 00 00 00 00 2c 00 00 01 ...(........,...
b2 6d b2 0e 81 88 ff ff 00 00 00 00 00 00 00 00 .m..............
backtrace (crc 6cdefeb4):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
__kmalloc_cache_noprof+0x359/0x440 mm/slub.c:5480
_kmalloc_noprof include/linux/slab.h:988 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
iommufd_fops_open+0x24/0xe0 drivers/iommu/iommufd/main.c:319
misc_open+0x12a/0x1f0 drivers/char/misc.c:163
chrdev_open+0x108/0x310 fs/char_dev.c:411
do_dentry_open+0x1fc/0x850 fs/open.c:996
vfs_open+0x3d/0x1b0 fs/open.c:1101
do_open fs/namei.c:4837 [inline]
path_openat+0xde7/0x11f0 fs/namei.c:5000
do_file_open+0x121/0x200 fs/namei.c:5029
do_sys_openat2+0xa7/0x150 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x82/0xf0 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff888127dd4000 (size 256):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
01 00 00 00 01 00 00 00 04 00 00 00 01 00 00 00 ................
00 00 00 00 00 00 00 00 01 48 cf 0a 81 88 ff ff .........H......
backtrace (crc 98731819):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
__do_kmalloc_node mm/slub.c:5336 [inline]
__kmalloc_noprof+0x3c2/0x560 mm/slub.c:5362
_kmalloc_noprof include/linux/slab.h:992 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
_iommufd_object_alloc+0x24/0x100 drivers/iommu/iommufd/main.c:41
iommufd_ioas_alloc drivers/iommu/iommufd/ioas.c:28 [inline]
iommufd_ioas_alloc_ioctl+0x46/0x160 drivers/iommu/iommufd/ioas.c:47
iommufd_fops_ioctl+0x1ed/0x370 drivers/iommu/iommufd/main.c:556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0xf4/0x140 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff88810eb26db0 (size 576):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
00 17 02 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
88 cd 61 11 81 88 ff ff c8 6d b2 0e 81 88 ff ff ..a......m......
backtrace (crc f41786a5):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
kmem_cache_alloc_lru_noprof+0x350/0x440 mm/slub.c:4952
xas_alloc+0xf1/0x110 lib/xarray.c:378
xas_expand lib/xarray.c:590 [inline]
xas_create+0x105/0x8a0 lib/xarray.c:661
xas_store+0x7a/0xb20 lib/xarray.c:795
__xa_alloc+0xec/0x200 lib/xarray.c:2005
xa_alloc include/linux/xarray.h:878 [inline]
_iommufd_object_alloc+0x9d/0x100 drivers/iommu/iommufd/main.c:56
iommufd_ioas_alloc drivers/iommu/iommufd/ioas.c:28 [inline]
iommufd_ioas_alloc_ioctl+0x46/0x160 drivers/iommu/iommufd/ioas.c:47
iommufd_fops_ioctl+0x1ed/0x370 drivers/iommu/iommufd/main.c:556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0xf4/0x140 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff88811161ccc0 (size 192):
comm "syz.0.25", pid 6047, jiffies 4294943865
hex dump (first 32 bytes):
01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 21b0f99b):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4599 [inline]
slab_alloc_node mm/slub.c:4919 [inline]
__kmalloc_cache_noprof+0x359/0x440 mm/slub.c:5480
_kmalloc_noprof include/linux/slab.h:988 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
iopt_alloc_pages.part.0+0x2b/0x210 drivers/iommu/iommufd/pages.c:1375
iopt_alloc_pages drivers/iommu/iommufd/pages.c:1432 [inline]
iopt_alloc_file_pages+0x7c/0xf0 drivers/iommu/iommufd/pages.c:1425
iopt_map_file_pages+0x184/0x1e0 drivers/iommu/iommufd/io_pagetable.c:518
iommufd_ioas_map_file+0x152/0x2f0 drivers/iommu/iommufd/ioas.c:231
iommufd_fops_ioctl+0x1ed/0x370 drivers/iommu/iommufd/main.c:556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0xf4/0x140 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
connection error: failed to recv *flatrpc.ExecutorMessageRawT: read tcp 127.0.0.1:41845->127.0.0.1:36772: read: connection reset by peer
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 <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*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=*/0x1000, /*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)) {}
// socket$inet6_tcp arguments: [
// domain: const = 0xa (8 bytes)
// type: const = 0x1 (8 bytes)
// proto: const = 0x0 (4 bytes)
// ]
// returns sock_tcp6
syscall(__NR_socket, /*domain=*/0xaul, /*type=*/1ul, /*proto=*/0);
// openat$iommufd arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 69 6f 6d 6d 75 00} (length 0xb)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd_iommufd
memcpy((void*)0x200000000000, "/dev/iommu\000", 11);
res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000000000ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$IOMMU_IOAS_ALLOC arguments: [
// fd: fd_iommufd (resource)
// cmd: const = 0x3b81 (4 bytes)
// arg: ptr[in, iommu_ioas_alloc] {
// iommu_ioas_alloc {
// size: len = 0xc (4 bytes)
// flags: const = 0x0 (4 bytes)
// out_ioas_id: ioas_handle (resource)
// }
// }
// ]
*(uint32_t*)0x200000000040 = 0xc;
*(uint32_t*)0x200000000044 = 0;
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x3b81, /*arg=*/0x200000000040ul);
// ioctl arguments: [
// fd: fd (resource)
// cmd: int32 = 0x3b8f (4 bytes)
// arg: ptr[in, buffer] {
// buffer: {28 00 00 00 06 00 00 00 01 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 00 10} (length 0x1a)
// }
// ]
memcpy((void*)0x2000000000c0, "\x28\x00\x00\x00\x06\x00\x00\x00\x01\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10", 26);
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x3b8f, /*arg=*/0x2000000000c0ul);
return 0;
}
Reply: The bug is a memory leak caused by a circular reference when mapping the `/dev/iommu` file descriptor itself into an `ioas` object using the `IOMMU_IOAS_MAP_FILE` ioctl.
When `IOMMU_IOAS_MAP_FILE` is called with the file descriptor of `/dev/iommu`, the kernel calls `iopt_alloc_file_pages()`, which takes a reference to the `file` struct (`pages->file = get_file(file)`). This `pages` object is then attached to the `ioas` object's page table (`iopt`).
However, the `ioas` object itself is owned by the `iommufd_ctx`, which is tied to the `/dev/iommu` file descriptor. This creates a reference cycle:
`file (/dev/iommu)` -> `iommufd_ctx` -> `ioas` -> `iopt_area` -> `iopt_pages` -> `file (/dev/iommu)`.
When the user process exits or closes the file descriptor, the `file`'s reference count is decremented but does not reach zero because of the reference held by `iopt_pages`. As a result, the `iommufd_fops_release()` function is never called, and the `ioas` object is never destroyed, leading to a permanent memory leak of the `file`, `iommufd_ctx`, `ioas`, and associated page table structures.
**Exploitability:**
This is a pure memory leak (resource exhaustion) and does not lead to memory corruption, use-after-free, or information leaks. It is not exploitable for privilege escalation.
**Denial of Service:**
An attacker with access to `/dev/iommu` can repeatedly trigger this bug in a loop to leak kernel memory, eventually causing the system to run out of memory (OOM) and crash, leading to a Denial of Service.
**Access Restrictions:**
The `/dev/iommu` device node is typically created with `0660` permissions and is owned by `root:root` (or a specific group like `kvm`). Therefore, it is not accessible to a typical unprivileged user or from within a user namespace unless the user has been explicitly granted access to the device node.
|
| 6/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 11623
output: 29
thoughts: 529
Thoughts: **Memory Leak Analysis: IOMMU File Mapping**
Okay, so we've got a kernel memory leak report, which immediately grabs my attention. The trigger is in `iommufd_fops_ioctl`, specifically when handling `IOMMU_IOAS_MAP_FILE`, which is `cmd=0x3b8f`. The stack trace points to `iopt_alloc_pages` being the culprit, called through `iopt_alloc_file_pages` and ultimately from `iopt_map_file_pages`. Sounds like we're leaking pages during file mapping.
Let's break down the reproducer code. Looks like it's opening something, getting a file descriptor, and then hitting a couple of ioctls. The first ioctl looks like an allocation (IOMMU_IOAS_ALLOC, cmd=0x3b81). The second, *crucially*, is the `IOMMU_IOAS_MAP_FILE` which is where the leak happens. We'll examine the memory regions being set up here to understand the context of what's being mapped.
Now, let's dive into the code. Time to check `drivers/iommu/iommufd/ioas.c` and specifically trace the path through `iommufd_ioas_map_file` to understand exactly what `iopt_map_file_pages` is doing, and why those pages aren't being freed correctly. I'll need to look at how the file descriptor interacts with the IOMMU subsystem, how the memory is allocated, and where the deallocation should be happening. Hopefully, it's a simple reference count issue or a missed cleanup path. It could be something subtly wrong with the page table manipulations, or perhaps some error handling that doesn't unwind the allocations correctly. Let's dig in.
|
| 7/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommufd_ioas_map_file]
Results: map[SourceCode: 204: int iommufd_ioas_map_file(struct iommufd_ucmd *ucmd)
205: {
206: struct iommu_ioas_map_file *cmd = ucmd->cmd;
207: unsigned long iova = cmd->iova;
208: struct iommufd_ioas *ioas;
209: unsigned int flags = 0;
210: int rc;
211:
212: if (cmd->flags &
213: ~(IOMMU_IOAS_MAP_FIXED_IOVA | IOMMU_IOAS_MAP_WRITEABLE |
214: IOMMU_IOAS_MAP_READABLE))
215: return -EOPNOTSUPP;
216:
217: if (cmd->iova >= ULONG_MAX || cmd->length >= ULONG_MAX)
218: return -EOVERFLOW;
219:
220: if (!(cmd->flags &
221: (IOMMU_IOAS_MAP_WRITEABLE | IOMMU_IOAS_MAP_READABLE)))
222: return -EINVAL;
223:
224: ioas = iommufd_get_ioas(ucmd->ictx, cmd->ioas_id);
225: if (IS_ERR(ioas))
226: return PTR_ERR(ioas);
227:
228: if (!(cmd->flags & IOMMU_IOAS_MAP_FIXED_IOVA))
229: flags = IOPT_ALLOC_IOVA;
230:
231: rc = iopt_map_file_pages(ucmd->ictx, &ioas->iopt, &iova, cmd->fd,
232: cmd->start, cmd->length,
233: conv_iommu_prot(cmd->flags), flags);
234: if (rc)
235: goto out_put;
236:
237: cmd->iova = iova;
238: rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
239: out_put:
240: iommufd_put_object(ucmd->ictx, &ioas->obj);
241: return rc;
242: }
SourceFile:drivers/iommu/iommufd/ioas.c]
|
| 8/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 13284
output: 26
thoughts: 34
Thoughts: Okay, let's dive into this. Here's how I'd approach that snippet of code, assuming I'm looking at `drivers/iommu/iommufd/io_pagetable.c`:
**Initial Code Inspection**
Right, so the first thing I need to do is get my bearings. The task is to examine `iopt_map_file_pages`. I know it's in the `io_pagetable.c` file, which probably deals with the IOMMU File Descriptor driver's implementation of page table management. Given the function name, I'm expecting this function is responsible for mapping file pages, presumably from a file backed by some storage, into the IOMMU's page table. That suggests the core functionality lies in setting up the necessary physical address translations so the IOMMU can correctly handle memory accesses to data from the file.
Now, I need to understand the context. What's the overall architecture? Is this a traditional IOMMU with a DMA-capable device? Or perhaps a more advanced setup? The `io_pagetable.c` filename indicates that the code is related to an IOMMU, it could be a hardware IOMMU or a software emulation of one. I'll need to remember to look at the surrounding code to determine how this interacts with the actual file system, and how the file is opened/mapped in the first place.
I need to quickly assess the core functions:
* What parameters does the function take? Any pointers to key data structures?
* What does it *do*? I'll look for memory mapping operations, page table manipulations, potential error handling, and maybe some interaction with the file system.
* How is it called? A quick `grep` will show me the calling contexts in other parts of the driver.
Okay, let's see what's in there.
|
| 9/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_map_file_pages]
Results: map[SourceCode: 470: /**
471: * iopt_map_file_pages() - Like iopt_map_user_pages, but map a file.
472: * @ictx: iommufd_ctx the iopt is part of
473: * @iopt: io_pagetable to act on
474: * @iova: If IOPT_ALLOC_IOVA is set this is unused on input and contains
475: * the chosen iova on output. Otherwise is the iova to map to on input
476: * @fd: fdno of a file to map
477: * @start: map file starting at this byte offset
478: * @length: Number of bytes to map
479: * @iommu_prot: Combination of IOMMU_READ/WRITE/etc bits for the mapping
480: * @flags: IOPT_ALLOC_IOVA or zero
481: */
482: int iopt_map_file_pages(struct iommufd_ctx *ictx, struct io_pagetable *iopt,
483: unsigned long *iova, int fd, unsigned long start,
484: unsigned long length, int iommu_prot,
485: unsigned int flags)
486: {
487: struct iopt_pages *pages;
488: struct dma_buf *dmabuf;
489: unsigned long start_byte;
490: unsigned long last;
491:
492: if (!length)
493: return -EINVAL;
494: if (check_add_overflow(start, length - 1, &last))
495: return -EOVERFLOW;
496:
497: start_byte = start - ALIGN_DOWN(start, PAGE_SIZE);
498: if (IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
499: dmabuf = dma_buf_get(fd);
500: else
501: dmabuf = ERR_PTR(-ENXIO);
502:
503: if (!IS_ERR(dmabuf)) {
504: pages = iopt_alloc_dmabuf_pages(ictx, dmabuf, start_byte, start,
505: length,
506: iommu_prot & IOMMU_WRITE);
507: if (IS_ERR(pages)) {
508: dma_buf_put(dmabuf);
509: return PTR_ERR(pages);
510: }
511: } else {
512: struct file *file;
513:
514: file = fget(fd);
515: if (!file)
516: return -EBADF;
517:
518: pages = iopt_alloc_file_pages(file, start_byte, start, length,
519: iommu_prot & IOMMU_WRITE);
520: fput(file);
521: if (IS_ERR(pages))
522: return PTR_ERR(pages);
523: }
524:
525: return iopt_map_common(ictx, iopt, pages, iova, length,
526: start_byte, iommu_prot, flags);
527: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 10/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 14727
output: 26
thoughts: 31
Thoughts: Here's my take on those thoughts, tailored for an expert audience:
**Diving into iopt_alloc_file_pages**
Okay, time to get my hands dirty. I need to take a look at the `iopt_alloc_file_pages` function. It's in `drivers/iommu/iommufd/pages.c`, which makes sense given its name and likely role in managing file-backed pages within the IOMMU framework. I'm assuming this is the core function for allocating page structures for use with IOMMU FD (File Descriptor) mappings. I'll need to understand how it interacts with the underlying page allocation mechanisms, how it handles potential errors (especially NUMA-related issues), and how it coordinates with the IOMMU hardware itself. I'll also be looking for any potential synchronization issues or memory leaks. Hopefully it follows best practices for page allocation within the kernel, given the high-performance and security implications of IOMMU operations. I'm curious to see how the code handles different page sizes and memory policies, and what optimizations are in place for frequently used configurations. Let's see what's in there.
|
| 11/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_alloc_file_pages]
Results: map[SourceCode:1417: struct iopt_pages *iopt_alloc_file_pages(struct file *file,
1418: unsigned long start_byte,
1419: unsigned long start,
1420: unsigned long length, bool writable)
1421:
1422: {
1423: struct iopt_pages *pages;
1424:
1425: pages = iopt_alloc_pages(start_byte, length, writable);
1426: if (IS_ERR(pages))
1427: return pages;
1428: pages->file = get_file(file);
1429: pages->start = start - start_byte;
1430: pages->type = IOPT_ADDRESS_FILE;
1431: return pages;
1432: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 12/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 15290
output: 24
thoughts: 29
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `iopt_alloc_pages`**
Okay, time to dig into the guts of the `iommufd` driver. I need to refresh my memory on how page allocation is handled, especially within the context of the IOMMU. Let's start with `iopt_alloc_pages`, the likely candidate for page allocation, specifically in `drivers/iommu/iommufd/pages.c`. I expect to see the typical allocation mechanisms, but I'm curious about the specific optimizations or constraints this driver might impose given its role in user-space IOMMU emulation. Are we dealing with huge pages? Are there any special considerations for physical address contiguity or caching behavior? My intuition tells me to expect a layered approach, perhaps leveraging the kernel's underlying page allocators but adding some IOMMU-specific metadata or mappings. Let's see if my assumptions hold water.
|
| 13/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_alloc_pages]
Results: map[SourceCode:1363: static struct iopt_pages *iopt_alloc_pages(unsigned long start_byte,
1364: unsigned long length, bool writable)
1365: {
1366: struct iopt_pages *pages;
1367:
1368: /*
1369: * The iommu API uses size_t as the length, and protect the DIV_ROUND_UP
1370: * below from overflow
1371: */
1372: if (length > SIZE_MAX - PAGE_SIZE || length == 0)
1373: return ERR_PTR(-EINVAL);
1374:
1375: pages = kzalloc_obj(*pages, GFP_KERNEL_ACCOUNT);
1376: if (!pages)
1377: return ERR_PTR(-ENOMEM);
1378:
1379: kref_init(&pages->kref);
1380: xa_init_flags(&pages->pinned_pfns, XA_FLAGS_ACCOUNT);
1381: mutex_init(&pages->mutex);
1382: pages->source_mm = current->mm;
1383: mmgrab(pages->source_mm);
1384: pages->npages = DIV_ROUND_UP(length + start_byte, PAGE_SIZE);
1385: pages->access_itree = RB_ROOT_CACHED;
1386: pages->domains_itree = RB_ROOT_CACHED;
1387: pages->writable = writable;
1388: if (capable(CAP_IPC_LOCK))
1389: pages->account_mode = IOPT_PAGES_ACCOUNT_NONE;
1390: else
1391: pages->account_mode = IOPT_PAGES_ACCOUNT_USER;
1392: pages->source_task = current->group_leader;
1393: get_task_struct(current->group_leader);
1394: pages->source_user = get_uid(current_user());
1395: return pages;
1396: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 14/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 16146
output: 24
thoughts: 63
Thoughts: Here's my understanding, breaking down the flow:
**Allocation and Mapping Process**
Okay, so I see this sequence. Essentially, `iopt_alloc_pages` is the foundational function, responsible for the initial allocation of memory pages. It's the one handing out the pages, the raw materials, if you will, and then *returning* a pointer to those allocated pages.
That pointer is then immediately used by `iopt_alloc_file_pages`. This function seemingly acts as an intermediary, taking those allocated pages and passing them along to `iopt_map_file_pages`. So, it's taking the low-level allocation and preparing it for... file mapping, based on the name.
Finally, `iopt_map_file_pages` does the actual heavy lifting with `iopt_map_common`. The name "common" suggests there's shared functionality between various mapping strategies, so `iopt_map_common` is likely where the real work of establishing the file-page link happens, whatever the nuances of those mappings. I'll need to dig into the implementation of `iopt_map_common` to fully understand what's going on, but now I know where to look.
|
| 15/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_map_common]
Results: map[SourceCode: 408: static int iopt_map_common(struct iommufd_ctx *ictx, struct io_pagetable *iopt,
409: struct iopt_pages *pages, unsigned long *iova,
410: unsigned long length, unsigned long start_byte,
411: int iommu_prot, unsigned int flags)
412: {
413: struct iopt_pages_list elm = {};
414: LIST_HEAD(pages_list);
415: int rc;
416:
417: elm.pages = pages;
418: elm.start_byte = start_byte;
419: if (ictx->account_mode == IOPT_PAGES_ACCOUNT_MM &&
420: elm.pages->account_mode == IOPT_PAGES_ACCOUNT_USER)
421: elm.pages->account_mode = IOPT_PAGES_ACCOUNT_MM;
422: elm.length = length;
423: list_add(&elm.next, &pages_list);
424:
425: rc = iopt_map_pages(iopt, &pages_list, length, iova, iommu_prot, flags);
426: if (rc) {
427: if (elm.area)
428: iopt_abort_area(elm.area);
429: if (elm.pages)
430: iopt_put_pages(elm.pages);
431: return rc;
432: }
433: return 0;
434: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 16/2 |
2026/08/22 15:15 |
llm |
expert |
0m
Model:
Tokens:
input: 16980
output: 24
thoughts: 65
Thoughts: **My Analysis of the `iopt_map_common` Function**
Okay, so `iopt_map_common` seems to be the central piece here. It's calling `iopt_map_pages`. The interesting part is what happens on failure: it calls `iopt_put_pages(elm.pages)`. Ah, right, the memory management... I remember that, the `elm.pages` variable is initialized to `pages`. That's important. It indicates that if `iopt_map_pages` has a problem, it needs to free the pages it (presumably) allocated. Let's delve into what `iopt_map_pages` actually *does* - that's where the real logic is likely hiding. I need to understand what its expectations are and where it might be running into issues. Time to investigate that next!
|
| 17/2 |
2026/08/22 15:15 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode: 374: int iopt_map_pages(struct io_pagetable *iopt, struct list_head *pages_list,
375: unsigned long length, unsigned long *dst_iova,
376: int iommu_prot, unsigned int flags)
377: {
378: struct iopt_pages_list *elm;
379: int rc;
380:
381: rc = iopt_alloc_area_pages(iopt, pages_list, length, dst_iova,
382: iommu_prot, flags);
383: if (rc)
384: return rc;
385:
386: down_read(&iopt->domains_rwsem);
387: rc = iopt_fill_domains_pages(pages_list);
388: if (rc)
389: goto out_unlock_domains;
390:
391: down_write(&iopt->iova_rwsem);
392: list_for_each_entry(elm, pages_list, next) {
393: /*
394: * area->pages must be set inside the domains_rwsem to ensure
395: * any newly added domains will get filled. Moves the reference
396: * in from the list.
397: */
398: elm->area->pages = elm->pages;
399: elm->pages = NULL;
400: elm->area = NULL;
401: }
402: up_write(&iopt->iova_rwsem);
403: out_unlock_domains:
404: up_read(&iopt->domains_rwsem);
405: return rc;
406: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 18/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 17790
output: 26
thoughts: 142
Thoughts: **Analyzing the Memory Allocation Workflow**
Okay, so `iopt_map_pages` is supposed to clean up `elm->pages` by setting it to `NULL` on success. That's good practice, makes sense. But, hang on... if `iopt_fill_domains_pages` has a problem and fails, `elm->pages` *isn't* set to `NULL`. Interesting. It leaves `elm->pages` alone. Then, `iopt_map_pages` returns the result code, `rc`. Right.
Now, if `iopt_map_common` sees that `rc` is not zero, it does a bit of cleanup: calls `iopt_abort_area(elm.area)` and then tries to clean up `iopt_put_pages(elm.pages)`. That's where things get potentially messy. If `iopt_fill_domains_pages` fails, then `elm->pages` might still contain stuff. And since `iopt_put_pages` could have problems with potentially uninitialized data. Hmm...
Hold on, I need to double-check something. Let me go back and re-read `iopt_alloc_area_pages`. It seems like `iopt_alloc_area_pages` is responsible for setting `elm->area` - I'm assuming that function handles the potential mapping failure if there's an error.
|
| 19/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_alloc_area_pages]
Results: map[SourceCode: 256: static int iopt_alloc_area_pages(struct io_pagetable *iopt,
257: struct list_head *pages_list,
258: unsigned long length, unsigned long *dst_iova,
259: int iommu_prot, unsigned int flags)
260: {
261: struct iopt_pages_list *elm;
262: unsigned long start;
263: unsigned long iova;
264: int rc = 0;
265:
266: list_for_each_entry(elm, pages_list, next) {
267: elm->area = iopt_area_alloc();
268: if (!elm->area)
269: return -ENOMEM;
270: }
271:
272: down_write(&iopt->iova_rwsem);
273: if ((length & (iopt->iova_alignment - 1)) || !length) {
274: rc = -EINVAL;
275: goto out_unlock;
276: }
277:
278: if (flags & IOPT_ALLOC_IOVA) {
279: /* Use the first entry to guess the ideal IOVA alignment */
280: elm = list_first_entry(pages_list, struct iopt_pages_list,
281: next);
282: switch (elm->pages->type) {
283: case IOPT_ADDRESS_USER:
284: start = elm->start_byte + (uintptr_t)elm->pages->uptr;
285: break;
286: case IOPT_ADDRESS_FILE:
287: start = elm->start_byte + elm->pages->start;
288: break;
289: case IOPT_ADDRESS_DMABUF:
290: start = elm->start_byte + elm->pages->dmabuf.start;
291: break;
292: }
293: rc = iopt_alloc_iova(iopt, dst_iova, start, length);
294: if (rc)
295: goto out_unlock;
296: if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
297: WARN_ON(iopt_check_iova(iopt, *dst_iova, length))) {
298: rc = -EINVAL;
299: goto out_unlock;
300: }
301: } else {
302: rc = iopt_check_iova(iopt, *dst_iova, length);
303: if (rc)
304: goto out_unlock;
305: }
306:
307: /*
308: * Areas are created with a NULL pages so that the IOVA space is
309: * reserved and we can unlock the iova_rwsem.
310: */
311: iova = *dst_iova;
312: list_for_each_entry(elm, pages_list, next) {
313: rc = iopt_insert_area(iopt, elm->area, elm->pages, iova,
314: elm->start_byte, elm->length, iommu_prot);
315: if (rc)
316: goto out_unlock;
317: iova += elm->length;
318: }
319:
320: out_unlock:
321: up_write(&iopt->iova_rwsem);
322: return rc;
323: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 20/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 19337
output: 24
thoughts: 1016
Thoughts: **Analyzing the `iopt_map_common` Function and Page Allocation**
Okay, let's break this down. My initial thought process is centered around how page allocation and error handling are managed in the `iopt_map_common` function. It seems `iopt_alloc_area_pages` allocates `elm->area` for each `elm` in `pages_list`. If this fails, for whatever reason, the `rc` is returned, and `iopt_map_pages` also returns that `rc`. Now, `iopt_map_common` checks the return code (`rc != 0`).
My next concern is about that `elm` variable within `iopt_map_common`. It's a local variable! I see that `elm` is initialized, its data members are set, and its address is added to the `pages_list`. Then, `iopt_map_pages` is called.
The key question that jumps out is, what does `iopt_map_pages` do with that `elm`? Because `iopt_map_pages` modifies `elm->pages` and `elm->area`. I spot this code in `iopt_map_pages`:
```c
down_write(&iopt->iova_rwsem);
list_for_each_entry(elm, pages_list, next) {
elm->area->pages = elm->pages;
elm->pages = NULL;
elm->area = NULL;
}
up_write(&iopt->iova_rwsem);
```
Ah! So, the `elm` within `iopt_map_pages` is a pointer to the `struct iopt_pages_list`. This code essentially takes ownership of the allocated `area` and `pages`. `elm->pages` and `elm->area` are then set to NULL, and the original pointer `elm` is now pointing to a different set of `pages` and `area`, since it has updated the data members.
Now, if `iopt_map_pages` fails, does it correctly clean up the `elm->area`? That's what I'm focused on. If `iopt_alloc_area_pages` fails, it returns `rc`. Let's say `iopt_alloc_area_pages` fails with `-EINVAL`, the function returns, and `iopt_map_common` will run:
```c
if (rc) {
if (elm.area)
iopt_abort_area(elm.area);
if (elm.pages)
iopt_put_pages(elm.pages);
return rc;
}
```
Okay, so I see `iopt_abort_area` and `iopt_put_pages` called, they free the `elm.area` and `elm.pages` respectively. But that `elm` there is a local variable, not the original data members!
My thought now is, what happens if `iopt_alloc_area_pages` fails inside `iopt_insert_area`? We need to keep this in mind. This is an important detail.
|
| 21/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_insert_area]
Results: map[SourceCode: 206: /*
207: * The area takes a slice of the pages from start_bytes to start_byte + length
208: */
209: static int iopt_insert_area(struct io_pagetable *iopt, struct iopt_area *area,
210: struct iopt_pages *pages, unsigned long iova,
211: unsigned long start_byte, unsigned long length,
212: int iommu_prot)
213: {
214: lockdep_assert_held_write(&iopt->iova_rwsem);
215:
216: if ((iommu_prot & IOMMU_WRITE) && !pages->writable)
217: return -EPERM;
218:
219: area->iommu_prot = iommu_prot;
220: area->page_offset = start_byte % PAGE_SIZE;
221: if (area->page_offset & (iopt->iova_alignment - 1))
222: return -EINVAL;
223:
224: area->node.start = iova;
225: if (check_add_overflow(iova, length - 1, &area->node.last))
226: return -EOVERFLOW;
227:
228: area->pages_node.start = start_byte / PAGE_SIZE;
229: if (check_add_overflow(start_byte, length - 1, &area->pages_node.last))
230: return -EOVERFLOW;
231: area->pages_node.last = area->pages_node.last / PAGE_SIZE;
232: if (WARN_ON(area->pages_node.last >= pages->npages))
233: return -EOVERFLOW;
234:
235: /*
236: * The area is inserted with a NULL pages indicating it is not fully
237: * initialized yet.
238: */
239: area->iopt = iopt;
240: interval_tree_insert(&area->node, &iopt->area_itree);
241: return 0;
242: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 22/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 21730
output: 24
thoughts: 83
Thoughts: **My Troubleshooting Flow**
Okay, so I'm chasing down an error here. It seems like the `iopt_insert_area` function is the initial point of failure – if that kicks back an error, we're in trouble. From there, `iopt_alloc_area_pages` and `iopt_map_pages` get involved and return their respective return codes, `rc`. Then, `iopt_map_common` tries to clean things up a bit by calling `iopt_abort_area(elm.area)`. Since we're dealing with an error scenario, my instinct is to dig into `iopt_abort_area` to understand what kind of cleanup it's attempting and what might be going wrong there. It's the logical next step in tracing the issue. Let's see what's happening in that function.
|
| 23/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_abort_area]
Results: map[SourceCode: 325: static void iopt_abort_area(struct iopt_area *area)
326: {
327: if (IS_ENABLED(CONFIG_IOMMUFD_TEST))
328: WARN_ON(area->pages);
329: if (area->iopt) {
330: down_write(&area->iopt->iova_rwsem);
331: interval_tree_remove(&area->node, &area->iopt->area_itree);
332: up_write(&area->iopt->iova_rwsem);
333: }
334: kfree(area);
335: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 24/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 22245
output: 26
thoughts: 96
Thoughts: **My Analysis of a Potential Memory Allocation Issue**
Okay, let me break this down. My initial concern is a bit complex. If `iopt_alloc_area_pages` fails during the `iopt_insert_area` process, I need to consider if partial area insertions are a possibility. The situation changes based on the context of the `pages_list`. Specifically, multiple elements in `pages_list` with multiple allocations.
But then, I remember something crucial: `iopt_map_common` *only* deals with a single element within that `pages_list`. This means the `list_for_each_entry` loop, that iterates through the list, will execute just once, no matter what. So that simplifies things... a little.
Now, a new problem arises: What if `iopt_fill_domains_pages` fails instead? That becomes another critical point of failure that I need to analyze. My thought process needs to account for all failure scenarios during this area handling.
|
| 25/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_fill_domains_pages]
Results: map[SourceCode: 352: static int iopt_fill_domains_pages(struct list_head *pages_list)
353: {
354: struct iopt_pages_list *undo_elm;
355: struct iopt_pages_list *elm;
356: int rc;
357:
358: list_for_each_entry(elm, pages_list, next) {
359: rc = iopt_area_fill_domains(elm->area, elm->pages);
360: if (rc)
361: goto err_undo;
362: }
363: return 0;
364:
365: err_undo:
366: list_for_each_entry(undo_elm, pages_list, next) {
367: if (undo_elm == elm)
368: break;
369: iopt_area_unfill_domains(undo_elm->area, undo_elm->pages);
370: }
371: return rc;
372: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 26/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 22922
output: 24
thoughts: 256
Thoughts: **My Concerns about `iopt_map_pages` Error Handling**
Okay, so if `iopt_fill_domains_pages` fails, it's supposed to return an error code, `rc`. The code then jumps right into `iopt_map_pages` like so:
```c
rc = iopt_fill_domains_pages(pages_list);
if (rc)
goto out_unlock_domains;
```
That makes sense, and the function then also returns `rc`. But then, `iopt_map_common` gets called and calls `iopt_abort_area(elm.area)` and `iopt_put_pages(elm.pages)`. I need to think this through carefully. `iopt_abort_area` removes the memory area from `iopt->area_itree` and frees the area. But... hold on, wasn't the area *just* inserted into the `iopt->area_itree` by `iopt_alloc_area_pages`?
So, if `iopt_fill_domains_pages` fails, and `iopt_abort_area` gets called, it *removes* that area from `iopt->area_itree` – which seems correct. But here's a potential wrinkle: What if `iopt_map_common` is called with a `pages` structure that has `pages->file` set? Because `iopt_put_pages` is called, that means that it would free `pages`. I need to verify how `iopt_put_pages` handles a file-backed `pages` structure. I need to make sure this doesn't lead to any unexpected resource leaks or double-frees. This needs a closer look.
|
| 27/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode: 278: static inline void iopt_put_pages(struct iopt_pages *pages)
279: {
280: kref_put(&pages->kref, iopt_release_pages);
281: }
SourceFile:drivers/iommu/iommufd/io_pagetable.h]
|
| 28/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 23689
output: 24
thoughts: 12
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Investigating `iopt_release_pages`**
Okay, time to circle back to `iopt_release_pages`. Given the context, I need to consider a few immediate things. My primary concern here is likely memory management. I need to quickly ascertain the purpose and scope of this function, specifically, how it interacts with the VM subsystem, the physical page allocator, and any relevant data structures like page tables or zone structures. I want to see how memory is being de-allocated, released back to the system, or potentially freed for reuse within the current process or the entire system.
I'm mentally running through the typical scenarios: are these pages being immediately returned to the free list, or are there any intermediate steps like caching or deferral involved? Are there any potential issues around fragmentation or contention that I should be aware of? I will look for calls to this function. Then trace the execution. If this is part of a larger memory management system, I'm going to look to see what parts of the execution is being covered.
I need to quickly assess its potential for performance bottlenecks or memory leaks. Any interaction with DMA, I/O devices, or shared memory areas is especially important to watch. I am also thinking about locking and synchronization: what mutexes or spinlocks are involved, and what is the potential for deadlocks or race conditions?
I'm ready to dive into the code and start tracing the execution to answer these questions and better understand the overall memory lifecycle. I’ll start by following the function's definition and its callers. The goal is to rapidly build a mental model of its behavior and potential impact.
|
| 29/2 |
2026/08/22 15:16 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_release_pages]
Results: map[SourceCode:1651: void iopt_release_pages(struct kref *kref)
1652: {
1653: struct iopt_pages *pages = container_of(kref, struct iopt_pages, kref);
1654:
1655: WARN_ON(!RB_EMPTY_ROOT(&pages->access_itree.rb_root));
1656: WARN_ON(!RB_EMPTY_ROOT(&pages->domains_itree.rb_root));
1657: WARN_ON(pages->npinned);
1658: WARN_ON(!xa_empty(&pages->pinned_pfns));
1659: if (iopt_is_dmabuf(pages) && pages->dmabuf.attach) {
1660: struct dma_buf *dmabuf = pages->dmabuf.attach->dmabuf;
1661:
1662: dma_resv_lock(dmabuf->resv, NULL);
1663: dma_buf_unpin(pages->dmabuf.attach);
1664: dma_resv_unlock(dmabuf->resv);
1665: dma_buf_detach(dmabuf, pages->dmabuf.attach);
1666: dma_buf_put(dmabuf);
1667: WARN_ON(!list_empty(&pages->dmabuf.tracker));
1668: } else if (pages->type == IOPT_ADDRESS_FILE) {
1669: fput(pages->file);
1670: }
1671: mmdrop(pages->source_mm);
1672: mutex_destroy(&pages->mutex);
1673: put_task_struct(pages->source_task);
1674: free_uid(pages->source_user);
1675: kfree(pages);
1676: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 30/2 |
2026/08/22 15:16 |
llm |
expert |
0m
Model:
Tokens:
input: 24615
output: 26
thoughts: 2536
Thoughts: **Analysis of File Page Mapping and Error Handling**
Okay, let me break this down. My initial concern was centered around potential race conditions and resource leaks during file page mapping, specifically within the `iopt_alloc_file_pages` and related functions. I needed to be sure about the correct reference counting and release of resources.
The flow in my mind starts with `iopt_alloc_file_pages`. I see that it takes a reference to the `file` using `get_file()`, which is good. Then the subsequent `fput(file)` happens *after* the allocation, so that's consistent and prevents a premature release, so this first sequence looks right. The error handling, where `iopt_put_pages` calls `iopt_release_pages`, which then calls `fput(pages->file)` and `kfree(pages)` seems correct, ensuring proper cleanup on failure before `iopt_map_common` is even called.
The critical path became `iopt_map_common` returning an error after a successful file allocation. The call stack involves the `iopt_map_pages` function, and how it handles potential errors. `iopt_map_pages` calls `iopt_alloc_area_pages`. Inside `iopt_alloc_area_pages`, `elm->area` is allocated. If it fails, that's handled at the caller and the function returns the error, but I had to be absolutely sure that no partially allocated `area` structures were left hanging.
I meticulously traced the logic. The local variable `elm` in `iopt_map_common` and `iopt_alloc_area_pages` plays a critical role here. `elm->area` is set in `iopt_alloc_area_pages`, and if allocation fails *during* the loop, the check `if (elm.area)` in `iopt_map_common` will correctly trigger `iopt_abort_area`, which frees the area.
Now, what if there's an error in `iopt_insert_area`? `iopt_insert_area` sets `area->iopt = iopt` *after* the error check. If the insert fails *before* it gets to the end (e.g., due to permissions or invalid arguments), `area->iopt` would remain NULL. The `iopt_abort_area` function checks if `area->iopt` is not NULL and then frees it, so that's good. If `iopt_insert_area` fails early, the corresponding `kfree` would happen safely. The crucial logic is that `area->iopt` being NULL means the area hasn't been fully initialized, and therefore doesn't need the other logic.
And, finally, if `iopt_insert_area` fails after multiple elements in `pages_list` are iterated (a hypothetical), the first element will be inserted correctly. However, that does not affect the ONE element in `iopt_map_common`.
All of this gives me a good degree of confidence that the error paths in the file page mapping and allocation routines are correctly handled. No resources are leaked, which is exactly what I wanted to verify.
|
| 31/2 |
2026/08/22 15:17 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_map_user_pages]
Results: map[SourceCode: 436: /**
437: * iopt_map_user_pages() - Map a user VA to an iova in the io page table
438: * @ictx: iommufd_ctx the iopt is part of
439: * @iopt: io_pagetable to act on
440: * @iova: If IOPT_ALLOC_IOVA is set this is unused on input and contains
441: * the chosen iova on output. Otherwise is the iova to map to on input
442: * @uptr: User VA to map
443: * @length: Number of bytes to map
444: * @iommu_prot: Combination of IOMMU_READ/WRITE/etc bits for the mapping
445: * @flags: IOPT_ALLOC_IOVA or zero
446: *
447: * iova, uptr, and length must be aligned to iova_alignment. For domain backed
448: * page tables this will pin the pages and load them into the domain at iova.
449: * For non-domain page tables this will only setup a lazy reference and the
450: * caller must use iopt_access_pages() to touch them.
451: *
452: * iopt_unmap_iova() must be called to undo this before the io_pagetable can be
453: * destroyed.
454: */
455: int iopt_map_user_pages(struct iommufd_ctx *ictx, struct io_pagetable *iopt,
456: unsigned long *iova, void __user *uptr,
457: unsigned long length, int iommu_prot,
458: unsigned int flags)
459: {
460: struct iopt_pages *pages;
461:
462: pages = iopt_alloc_user_pages(uptr, length, iommu_prot & IOMMU_WRITE);
463: if (IS_ERR(pages))
464: return PTR_ERR(pages);
465:
466: return iopt_map_common(ictx, iopt, pages, iova, length,
467: uptr - pages->uptr, iommu_prot, flags);
468: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 32/2 |
2026/08/22 15:17 |
llm |
expert |
0m
Model:
Tokens:
input: 28534
output: 24
thoughts: 46
Thoughts: Okay, here's my interpretation of those thoughts, framed as my own:
**Analyzing Memory Mapping Operations**
Alright, let's see. `iopt_map_user_pages` calls `iopt_map_common`. Now, what jumps out immediately is that `iopt_map_common` is dealing with *only one* element. That's a bit peculiar. I need to understand the relationship better.
The question then is, are there any other instances where `iopt_map_pages` is called and passed multiple elements? Knowing where the function is used is key. I need to quickly scan the call graph and usages of `iopt_map_pages`. The answer could change my mental model about how this part of the kernel operates. Let's dig in and find out.
|
| 33/2 |
2026/08/22 15:17 |
tool |
codesearch-find-references |
0m
Args:
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:iommufd_ioas_copy SourceFile:drivers/iommu/iommufd/ioas.c SourceLine:326] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:iopt_map_common SourceFile:drivers/iommu/iommufd/io_pagetable.c SourceLine:425]] TruncatedOutput:false]
|
| 34/2 |
2026/08/22 15:17 |
llm |
expert |
0m
Model:
Tokens:
input: 28916
output: 27
thoughts: 15
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Diving into `iommufd_ioas_copy`**
Alright, time to dive into `iommufd_ioas_copy`. This likely means I'm about to scrutinize the I/O memory management unit (IOMMU) file descriptor related code responsible for copying data between different address spaces, specifically the part that handles I/O address space (IOAS) copies. My initial thought process now will likely involve asking myself these questions in order to understand the flow:
1. *Where is this function called from*? Understanding the call stack provides context - is it triggered by a specific device driver, a user-space utility, or kernel-internal operations?
2. *What are the inputs and outputs*? I'll need to clearly understand the source and destination buffers/regions, any associated metadata, and the expected semantics (synchronization, error handling, etc.). The parameters passed to this function are key.
3. *What's the overall copy strategy*? Is it a direct memory access (DMA), is it a bounce buffer, or some other IOMMU-mediated scheme? Is the copy hardware-accelerated, or done through software translation?
4. *What are the locking semantics*? I'll need to pay close attention to the lock acquisition/release and how this function ensures data integrity and consistency, especially in a multi-threaded environment. Race conditions in the IOMMU code are particularly nasty.
5. *How are page tables involved*? Are page table mappings being updated, invalidating, or simply used? What's the process for invalidating/flushing the TLBs after making changes? Is there anything done to avoid TLB misses when the new mappings are being accessed?
6. *Are there any cache coherence considerations*? Proper handling of cache coherence is paramount, especially when copying data between devices with different cache policies.
7. *Error Handling*? The ability to detect and handle different error scenarios, such as IOMMU faults, memory allocation failures, or invalid input parameters, is important.
8. *What specific IOMMU features are being leveraged*? Depending on the architecture, there could be subtle differences in how the copy is happening.
9. *What is the impact on performance*? I will need to consider the overhead of the memory copy operation, whether there are any optimizations in place and what the potential bottlenecks are.
10. *Is this a critical path operation*? If it's on a time-sensitive path, I'll need to be extra vigilant about potential sources of latency and overhead.
I'm expecting this function to be a core piece of code, and understanding its details is fundamental to ensuring efficient and secure I/O operations. Let's see what we can find.
|
| 35/2 |
2026/08/22 15:17 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommufd_ioas_copy]
Results: map[SourceCode: 283: int iommufd_ioas_copy(struct iommufd_ucmd *ucmd)
284: {
285: struct iommu_ioas_copy *cmd = ucmd->cmd;
286: struct iommufd_ioas *src_ioas;
287: struct iommufd_ioas *dst_ioas;
288: unsigned int flags = 0;
289: LIST_HEAD(pages_list);
290: unsigned long iova;
291: int rc;
292:
293: iommufd_test_syz_conv_iova_id(ucmd, cmd->src_ioas_id, &cmd->src_iova,
294: &cmd->flags);
295:
296: if ((cmd->flags &
297: ~(IOMMU_IOAS_MAP_FIXED_IOVA | IOMMU_IOAS_MAP_WRITEABLE |
298: IOMMU_IOAS_MAP_READABLE)))
299: return -EOPNOTSUPP;
300: if (cmd->length >= ULONG_MAX || cmd->src_iova >= ULONG_MAX ||
301: cmd->dst_iova >= ULONG_MAX)
302: return -EOVERFLOW;
303:
304: if (!(cmd->flags &
305: (IOMMU_IOAS_MAP_WRITEABLE | IOMMU_IOAS_MAP_READABLE)))
306: return -EINVAL;
307:
308: src_ioas = iommufd_get_ioas(ucmd->ictx, cmd->src_ioas_id);
309: if (IS_ERR(src_ioas))
310: return PTR_ERR(src_ioas);
311: rc = iopt_get_pages(&src_ioas->iopt, cmd->src_iova, cmd->length,
312: &pages_list);
313: iommufd_put_object(ucmd->ictx, &src_ioas->obj);
314: if (rc)
315: return rc;
316:
317: dst_ioas = iommufd_get_ioas(ucmd->ictx, cmd->dst_ioas_id);
318: if (IS_ERR(dst_ioas)) {
319: rc = PTR_ERR(dst_ioas);
320: goto out_pages;
321: }
322:
323: if (!(cmd->flags & IOMMU_IOAS_MAP_FIXED_IOVA))
324: flags = IOPT_ALLOC_IOVA;
325: iova = cmd->dst_iova;
326: rc = iopt_map_pages(&dst_ioas->iopt, &pages_list, cmd->length, &iova,
327: conv_iommu_prot(cmd->flags), flags);
328: if (rc)
329: goto out_put_dst;
330:
331: cmd->dst_iova = iova;
332: rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
333: out_put_dst:
334: iommufd_put_object(ucmd->ictx, &dst_ioas->obj);
335: out_pages:
336: iopt_free_pages_list(&pages_list);
337: return rc;
338: }
SourceFile:drivers/iommu/iommufd/ioas.c]
|
| 36/2 |
2026/08/22 15:17 |
llm |
expert |
0m
Model:
Tokens:
input: 30619
output: 26
thoughts: 78
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing:
**Analyzing `iommufd_ioas_copy` and Page Management**
Right, let's see. `iommufd_ioas_copy` is calling `iopt_map_pages`, and that function's getting a `pages_list` argument, which, if I'm reading this correctly, *can* contain multiple pages. That's a key observation. Now, what happens if `iopt_map_pages` throws an error? Ah, it calls `iopt_free_pages_list(&pages_list)`. That's good defensive programming – ensuring we clean up any allocated pages on failure. My immediate focus then needs to be on how `iopt_free_pages_list` actually works. I need to understand that freeing logic, and any potential edge cases in it, before I can be comfortable. I'm especially interested in whether that freeing is safe and complete under all potential failure scenarios. That's the next line of inquiry.
|
| 37/2 |
2026/08/22 15:17 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_free_pages_list]
Results: map[SourceCode: 337: void iopt_free_pages_list(struct list_head *pages_list)
338: {
339: struct iopt_pages_list *elm;
340:
341: while ((elm = list_first_entry_or_null(pages_list,
342: struct iopt_pages_list, next))) {
343: if (elm->area)
344: iopt_abort_area(elm->area);
345: if (elm->pages)
346: iopt_put_pages(elm->pages);
347: list_del(&elm->next);
348: kfree(elm);
349: }
350: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 38/2 |
2026/08/22 15:17 |
llm |
expert |
0m
Model:
Tokens:
input: 31199
output: 28
thoughts: 1544
Thoughts: **Analyzing IOMMUFD Memory Management in the Context of a Potential Leak**
Okay, let's break this down systematically. I'm focusing on `iopt_free_pages_list` and its interactions, as it seems to be at the heart of the issue.
First, I'm checking the flow of `iopt_free_pages_list`. It calls `iopt_abort_area` if `elm->area` is set. Now, I'm trying to figure out if that will leak.
If `iopt_alloc_area_pages` fails during `iopt_insert_area`, it returns an error. Then `iopt_map_pages` returns an error, and finally, `iommufd_ioas_copy` calls `iopt_free_pages_list`. I need to understand what happens if allocation within the loop fails. If `iopt_area_alloc` fails for, say, the second element in the `pages_list`, the first element already has `elm->area` allocated. `iopt_free_pages_list` is called, it will call `iopt_abort_area` for that first element, then the second element will not have an area, so no problem. `iopt_abort_area` then releases memory using `kfree`, which is good. That's fine. If `iopt_area_alloc` fails.
Now I'm considering the more complex case: What if `iopt_insert_area` fails? If it fails for the second element, the first element's area *was* successfully inserted. `elm->area->iopt` is set in this case, and it is in `iopt->area_itree`. This also gets handled. `iopt_free_pages_list` then gets called. It calls `iopt_abort_area` for both elements. For the first one, which *was* inserted, the `iopt` field is set, so it's removed from the tree and freed. For the second one, which *wasn't* inserted, the `iopt` field is still NULL, so it just gets freed. This works. The logic appears correct.
Next I'm checking a different failure point: What if `iopt_fill_domains_pages` fails? If this happens, it returns an error, and then `iopt_free_pages_list` runs. Again, it calls `iopt_abort_area`. All the elements were successfully inserted into the tree. So `iopt_abort_area` removes them from the tree and frees them. Good. That's also handled.
So, *where* is the memory leak? I thought that the memory leak was in `iopt_alloc_pages`, `iommufd_ioas_alloc`, `xas_alloc`, `security_file_alloc`, `alloc_empty_file` but based on the code I am looking at I do not see the leak there.
Looking at the reproducer: it opens `/dev/iommu`, and does `IOMMU_IOAS_ALLOC`, then `IOMMU_IOAS_MAP_FILE`. The `IOMMU_IOAS_MAP_FILE` ioctl call has some strange looking arguments. I should focus on `IOMMU_IOAS_MAP_FILE` itself. What does it pass?
I see a memory copy into some address. Examining the data reveals something that is likely a `iommu_ioas_map_file` struct. The byte 0x10 is suspicious.
|
| 39/2 |
2026/08/22 15:17 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommu_ioas_map_file]
Results: map[SourceCode: 250: /**
251: * struct iommu_ioas_map_file - ioctl(IOMMU_IOAS_MAP_FILE)
252: * @size: sizeof(struct iommu_ioas_map_file)
253: * @flags: same as for iommu_ioas_map
254: * @ioas_id: same as for iommu_ioas_map
255: * @fd: the memfd or supported dma-buf file to map
256: * @start: byte offset from start of the file to map from
257: * @length: same as for iommu_ioas_map
258: * @iova: same as for iommu_ioas_map
259: *
260: * Set an IOVA mapping from a memfd file. On kernels with dma-buf support,
261: * supported dma-buf files may also be accepted. This is not a generic
262: * dma-buf import path; currently supported dma-bufs include single-range
263: * VFIO PCI dma-bufs exported through VFIO_DEVICE_FEATURE_DMA_BUF, and
264: * other dma-bufs may be rejected. All other arguments and semantics match
265: * those of IOMMU_IOAS_MAP.
266: */
267: struct iommu_ioas_map_file {
268: __u32 size;
269: __u32 flags;
270: __u32 ioas_id;
271: __s32 fd;
272: __aligned_u64 start;
273: __aligned_u64 length;
274: __aligned_u64 iova;
275: };
SourceFile:include/uapi/linux/iommufd.h]
|
| 40/2 |
2026/08/22 15:17 |
llm |
expert |
0m
Model:
Tokens:
input: 34078
output: 27
thoughts: 1229
Thoughts: **Decoding the IOMMU IOAS Map File Request**
Okay, let's break this down. We're looking at a memory map request for the IOMMU, represented as a series of bytes. First, we have the size: `\x28\x00\x00\x00`, which translates to 40 bytes. Then we see the flags: `\x06\x00\x00\x00`, this corresponds to `IOMMU_IOAS_MAP_WRITEABLE | IOMMU_IOAS_MAP_READABLE`. The `ioas_id` is `1` (`\x01\x00\x00\x00`) and the file descriptor (`fd`) is `4` (`\x04\x00\x00\x00`). The starting address `start` is zero, represented by all zeros. Now, the length. This is where it gets interesting because the length seems truncated: we see only `\x00\x10`, but the expected length is `0x1000`. We know `memcpy` only copies 26 bytes, and the `iommufd_fops_ioctl` will copy `size` bytes from userspace. It will initialize the unused parts with zeros since the memory is mapped as `MAP_ANONYMOUS`. This means the provided `\x00\x10` at offset 24 will get interpreted as the beginning of the length field, so the full length is indeed 0x1000 (4096 bytes). Also, `iova` is initialized to `0`.
Now, the crucial point: `fd` is 4. The reproducer reveals this is not the usual socket file descriptor (fd=3), but the file descriptor returned by `openat` for `/dev/iommu`. This means `IOMMU_IOAS_MAP_FILE` is being called with the `/dev/iommu` file descriptor itself!
Let's trace what happens with `/dev/iommu`. In `iopt_map_file_pages`, the code attempts to use `dma_buf_get(fd)`. However, `/dev/iommu` isn't a DMA-BUF, so that fails. The code then falls back to `fget(fd)`. This retrieves a `struct file` pointer for the `/dev/iommu` file. Next, it calls `iopt_alloc_file_pages`, which allocates page structures and gets a reference to the `file`. This then calls `iopt_map_common`. The function `iopt_map_pages` allocates the pages into `iopt->area_itree`.
If `iopt_map_pages` succeeds, the function returns 0. That's good. In `iopt_map_common`, the success of `iopt_map_pages` will store `pages` in `area->pages`, and the `area` is added to `iopt->area_itree`. This `area` will be stored. Now, we need to make sure that the pages are cleaned up. We need to confirm whether `iommufd_ioas_destroy` frees the allocated areas and pages.
|
| 41/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommufd_ioas_destroy]
Results: map[SourceCode: 13: void iommufd_ioas_destroy(struct iommufd_object *obj)
14: {
15: struct iommufd_ioas *ioas = container_of(obj, struct iommufd_ioas, obj);
16: int rc;
17:
18: rc = iopt_unmap_all(&ioas->iopt, NULL);
19: WARN_ON(rc && rc != -ENOENT);
20: iopt_destroy_table(&ioas->iopt);
21: mutex_destroy(&ioas->mutex);
22: }
SourceFile:drivers/iommu/iommufd/ioas.c]
|
| 42/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 36258
output: 25
thoughts: 13
Thoughts: Okay, let's dive into this. Here's my thought process on this:
**Checking `iopt_unmap_all`**
Alright, time to get to work. Let's see... the task at hand is to check and understand how `iopt_unmap_all` functions. I know the core principle here – we're talking about unmapping memory, likely related to optimized I/O operations. Given my understanding of memory management and I/O optimization, I want to assess the logic and purpose of `iopt_unmap_all`. I'll analyze the code to get an understanding. What does it unmap? Why is it necessary? What potential errors or issues could arise, such as resource leaks or double frees, are there? I will also be looking to see if there is anything that is unexpected that I can provide an explanation for. Understanding this function could be key to ensuring the efficiency and stability of the system. Let's start digging in.
|
| 43/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode: 940: int iopt_unmap_all(struct io_pagetable *iopt, unsigned long *unmapped)
941: {
942: /* If the IOVAs are empty then unmap all succeeds */
943: return iopt_unmap_iova_range(iopt, 0, ULONG_MAX, unmapped);
944: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 44/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 36645
output: 28
thoughts: 16
Thoughts: Okay, let's dive into this. Here's my thought process on checking `iopt_unmap_iova_range`, summarized as requested:
**Diving into `iopt_unmap_iova_range`**
Alright, time to focus. I'm going to take a look at `iopt_unmap_iova_range`. I know this function is crucial. It's the one responsible for unmapping a range of IO Virtual Addresses (IOVAs). So, the core functionality here is about deallocating resources. I need to understand the specifics of how this function handles that unmapping process. I'm thinking about the implications if there are any race conditions to be aware of, perhaps some shared data it's touching, or what might happen if there are any errors during the unmapping. It's critical to make sure that the system is left in a consistent state and that no memory is leaked or corrupted. My main concerns revolve around correctness, performance, and robustness, as always. Let's see how it's implemented.
|
| 45/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_unmap_iova_range]
Results: map[SourceCode: 741: static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
742: unsigned long last, unsigned long *unmapped)
743: {
744: struct iopt_area *area;
745: unsigned long unmapped_bytes = 0;
746: unsigned int tries = 0;
747: /* If there are no mapped entries then success */
748: int rc = 0;
749:
750: /*
751: * The domains_rwsem must be held in read mode any time any area->pages
752: * is NULL. This prevents domain attach/detatch from running
753: * concurrently with cleaning up the area.
754: */
755: again:
756: down_read(&iopt->domains_rwsem);
757: down_write(&iopt->iova_rwsem);
758: while ((area = iopt_area_iter_first(iopt, start, last))) {
759: unsigned long area_last = iopt_area_last_iova(area);
760: unsigned long area_first = iopt_area_iova(area);
761: struct iopt_pages *pages;
762:
763: /* Userspace should not race map/unmap's of the same area */
764: if (!area->pages) {
765: rc = -EBUSY;
766: goto out_unlock_iova;
767: }
768:
769: /* The area is locked by an object that has not been destroyed */
770: if (area->num_locks) {
771: rc = -EBUSY;
772: goto out_unlock_iova;
773: }
774:
775: if (area_first < start || area_last > last) {
776: rc = -ENOENT;
777: goto out_unlock_iova;
778: }
779:
780: if (area_first != start)
781: tries = 0;
782:
783: /*
784: * num_accesses writers must hold the iova_rwsem too, so we can
785: * safely read it under the write side of the iovam_rwsem
786: * without the pages->mutex.
787: */
788: if (area->num_accesses) {
789: size_t length = iopt_area_length(area);
790:
791: start = area_first;
792: area->prevent_access = true;
793: up_write(&iopt->iova_rwsem);
794: up_read(&iopt->domains_rwsem);
795:
796: iommufd_access_notify_unmap(iopt, area_first, length);
797: /* Something is not responding to unmap requests. */
798: tries++;
799: if (WARN_ON(tries > 100)) {
800: rc = -EDEADLOCK;
801: goto out_unmapped;
802: }
803: goto again;
804: }
805:
806: pages = area->pages;
807: area->pages = NULL;
808: up_write(&iopt->iova_rwsem);
809:
810: iopt_area_unfill_domains(area, pages);
811: iopt_abort_area(area);
812: iopt_put_pages(pages);
813:
814: unmapped_bytes += area_last - area_first + 1;
815:
816: down_write(&iopt->iova_rwsem);
817:
818: /*
819: * After releasing the iova_rwsem concurrent allocation could
820: * place new areas at IOVAs we have already unmapped. Keep
821: * moving the start of the search forward to ignore the area
822: * already unmapped.
823: */
824: if (area_last >= last)
825: break;
826: start = area_last + 1;
827: }
828:
829: out_unlock_iova:
830: up_write(&iopt->iova_rwsem);
831: up_read(&iopt->domains_rwsem);
832: out_unmapped:
833: if (unmapped)
834: *unmapped = unmapped_bytes;
835: return rc;
836: }
SourceFile:drivers/iommu/iommufd/io_pagetable.c]
|
| 46/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 38339
output: 27
thoughts: 1505
Thoughts: **Analyzing a Potential Race Condition in IOMMU Unmapping**
Okay, let's break this down. My initial concern is with `iopt_unmap_iova_range`, specifically the check `if (!area->pages) { rc = -EBUSY; goto out_unlock_iova; }`. This seems like a critical path, and I need to understand when `area->pages` can be NULL.
I've traced the flow. `area->pages` is initialized as NULL in `iopt_insert_area`. It's only assigned in `iopt_map_pages`, where the value of `elm->pages` is assigned to `elm->area->pages`. However, `iopt_map_pages` relies on the success of `iopt_fill_domains_pages`, and if *that* fails, `elm->area->pages` *isn't* set. Then, `iopt_map_common` calls `iopt_abort_area(elm.area)`. `iopt_abort_area` removes the area from `iopt->area_itree`. So, if `iopt_map_pages` fails during the mapping process, the area is removed from the tree, and the unmap function won't find it. That seems safe.
But then there's another point in `iopt_unmap_iova_range` itself: the case where `area->pages` is explicitly set to NULL within the function itself, before `iopt_abort_area` is called. Specifically:
```c
pages = area->pages;
area->pages = NULL;
up_write(&iopt->iova_rwsem);
iopt_area_unfill_domains(area, pages);
iopt_abort_area(area);
iopt_put_pages(pages);
```
Here, it sets `area->pages = NULL`, releases the write lock on `iova_rwsem` and *then* calls `iopt_abort_area`. Now, `iopt_abort_area` takes `iova_rwsem` *again* to remove the area from the `area_itree`.
So the window is: the area is still in `area_itree`, but `area->pages` is NULL *between* the `up_write` and the `down_write` within `iopt_abort_area`. If another thread calls `iopt_unmap_iova_range` concurrently *during this window*, it will find the area in the tree, see `!area->pages`, and return `-EBUSY`! That's a definite race condition.
I need to think about the circumstances under which this might happen. `iopt_unmap_all` is called during `iommufd_ioas_destroy`, which is called when the `ioas` object is destroyed. My first thought is that there's not a direct concurrency issue there, because the refcount of the `ioas` object should prevent this. However, this relies on that the only function call to `iopt_unmap_iova_range` is from `iommufd_ioas_destroy`.
Then, I thought, maybe another `IOMMU_IOAS_UNMAP` ioctl could call this concurrently. If concurrent `IOMMU_IOAS_UNMAP` calls are made, then yes, one of them could very well return `-EBUSY`. But that's not what the reproducer does.
Now, I'm examining the reproducer itself. It opens a file descriptor to `/dev/iommu`, allocates an `ioas`, and then uses `IOMMU_IOAS_MAP_FILE` to map the *file itself* (the `/dev/iommu` file) into the IOMMU. This is a bit unusual. The key is what happens on process exit.
The process closes all file descriptors on exit. So, it's closing `fd` 4, which is the `/dev/iommu` file. But the ioas has a mapping to `fd` 4. When the program calls `IOMMU_IOAS_MAP_FILE`, the code increments the refcount of the underlying `file` struct for `/dev/iommu` via `get_file(file)`. This means the `file` struct won't be destroyed when `fd` 4 is closed because the refcount is > 0 (it is held by the ioas mapping). Since the `file` structure is not destroyed, its `release` function won't be called. The `release` function for `/dev/iommu` is `iommuf
|
| 47/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommufd_fops_release]
Results: map[SourceCode: 345: static int iommufd_fops_release(struct inode *inode, struct file *filp)
346: {
347: struct iommufd_ctx *ictx = filp->private_data;
348: struct iommufd_sw_msi_map *next;
349: struct iommufd_sw_msi_map *cur;
350: struct iommufd_object *obj;
351:
352: /*
353: * The objects in the xarray form a graph of "users" counts, and we have
354: * to destroy them in a depth first manner. Leaf objects will reduce the
355: * users count of interior objects when they are destroyed.
356: *
357: * Repeatedly destroying all the "1 users" leaf objects will progress
358: * until the entire list is destroyed. If this can't progress then there
359: * is some bug related to object refcounting.
360: */
361: while (!xa_empty(&ictx->objects)) {
362: unsigned int destroyed = 0;
363: unsigned long index;
364: bool empty = true;
365:
366: /*
367: * We can't use xa_empty() to end the loop as the tombstones
368: * are stored as XA_ZERO_ENTRY in the xarray. However
369: * xa_for_each() automatically converts them to NULL and skips
370: * them causing xa_empty() to be kept false. Thus once
371: * xa_for_each() finds no further !NULL entries the loop is
372: * done.
373: */
374: xa_for_each(&ictx->objects, index, obj) {
375: empty = false;
376: if (!refcount_dec_if_one(&obj->users))
377: continue;
378:
379: destroyed++;
380: xa_erase(&ictx->objects, index);
381: iommufd_object_ops[obj->type].destroy(obj);
382: kfree(obj);
383: }
384:
385: if (empty)
386: break;
387:
388: /* Bug related to users refcount */
389: if (WARN_ON(!destroyed))
390: break;
391: }
392:
393: /*
394: * There may be some tombstones left over from
395: * iommufd_object_tombstone_user()
396: */
397: xa_destroy(&ictx->objects);
398:
399: WARN_ON(!xa_empty(&ictx->groups));
400:
401: mutex_destroy(&ictx->sw_msi_lock);
402: list_for_each_entry_safe(cur, next, &ictx->sw_msi_list, sw_msi_item)
403: kfree(cur);
404:
405: kfree(ictx);
406: return 0;
407: }
SourceFile:drivers/iommu/iommufd/main.c]
|
| 48/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 41865
output: 26
thoughts: 842
Thoughts: **My Analysis of the IOMMU File Descriptor Memory Leak**
Okay, here's what I've figured out: `iommufd_fops_release` is supposed to clean up `ioas` objects, but it's only called when the file descriptor's reference count hits zero. The problem is, this *never* happens due to a circular reference. The `ioas` object holds a reference to the `file` object (specifically via `pages->file`), and, because of the data structures involved, the `file` (through `ictx->objects`) holds a reference to the `ioas`. This creates an eternal, unbreakable, loop!
Let me break down the process step-by-step to be sure. My reproducer opens `/dev/iommu` and gets an `fd`. It creates an `ioas` object tied to that `fd`. Then, `IOMMU_IOAS_MAP_FILE` is called with that `fd`. This triggers `iopt_map_file_pages`, which then calls `fget(4)` to get a reference to the `/dev/iommu` file. `iopt_alloc_file_pages` then calls `get_file(file)` and assigns it to `pages->file`. The pages are then mapped into the `ioas`. So far, so good, but here's where the problem arises: the `ioas` now has an `area` that points to `pages`, which points back to the `/dev/iommu` file.
When the process closes that `fd`, `fput(file)` is called. But the file refcount is 2 (fd table + `pages->file`). `fput` *decrements* the refcount to 1, and so `iommufd_fops_release` is *not* called. The `ictx->objects` is not destroyed, so the `ioas` persists, and neither does the `iopt` or `area`. This means the `/dev/iommu` file also persists, held by `pages`. This confirms it: It's a circular reference, a classic memory leak!
This is definitely exploitable, as it's a denial-of-service vulnerability through resource exhaustion. A user can create tons of these leaked objects by repeatedly opening `/dev/iommu`, mapping it, and closing the fd. Each instance leaks a `file`, an `ictx`, an `ioas`, an `iopt_pages`, an `iopt_area`, and the associated structures, ultimately leading to system instability and, potentially, a crash.
I've considered other mapping scenarios but the circular reference is really specific to mapping `/dev/iommu` itself. Mapping a memfd won't cause the circular reference, as memfd doesn't understand the IOMMU data structures. It seems the crux of the problem lies in the design of the mapping function, and how it handles the references to the underlying `/dev/iommu` file. The fact that the original `fd` is used with `IOMMU_IOAS_MAP_FILE` is central to triggering the issue. I need to review `iopt_alloc_file_pages` to confirm that my conclusions are correct.
|
| 49/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_alloc_file_pages]
Results: map[SourceCode:1417: struct iopt_pages *iopt_alloc_file_pages(struct file *file,
1418: unsigned long start_byte,
1419: unsigned long start,
1420: unsigned long length, bool writable)
1421:
1422: {
1423: struct iopt_pages *pages;
1424:
1425: pages = iopt_alloc_pages(start_byte, length, writable);
1426: if (IS_ERR(pages))
1427: return pages;
1428: pages->file = get_file(file);
1429: pages->start = start - start_byte;
1430: pages->type = IOPT_ADDRESS_FILE;
1431: return pages;
1432: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 50/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 43695
output: 26
thoughts: 54
Thoughts: Okay, let me think this through.
**Digging into File Page Allocation**
Alright, so `iopt_alloc_file_pages` just needs the `file` pointer, right? But that seems... incomplete. How does it *actually* get those pages from the file? I mean, it's not magic. There has to be a mechanism. Let's dig deeper. I need to understand how the data gets pinned, how it's brought into memory and mapped. I should probably look at something related to accessing the pages themselves – maybe a function called `iopt_access_pages` or something similar that handles the underlying pinning and mapping operations. I need to trace this sequence to understand the core logic.
|
| 51/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iopt_area_fill_domains]
Results: map[SourceCode:1893: /**
1894: * iopt_area_fill_domains() - Install PFNs into the area's domains
1895: * @area: The area to act on
1896: * @pages: The pages associated with the area (area->pages is NULL)
1897: *
1898: * Called during area creation. The area is freshly created and not inserted in
1899: * the domains_itree yet. PFNs are read and loaded into every domain held in the
1900: * area's io_pagetable and the area is installed in the domains_itree.
1901: *
1902: * On failure all domains are left unchanged.
1903: */
1904: int iopt_area_fill_domains(struct iopt_area *area, struct iopt_pages *pages)
1905: {
1906: unsigned long done_first_end_index;
1907: unsigned long done_all_end_index;
1908: struct iommu_domain *domain;
1909: unsigned long unmap_index;
1910: struct pfn_reader pfns;
1911: unsigned long index;
1912: int rc;
1913:
1914: lockdep_assert_held(&area->iopt->domains_rwsem);
1915:
1916: if (xa_empty(&area->iopt->domains))
1917: return 0;
1918:
1919: mutex_lock(&pages->mutex);
1920: if (iopt_is_dmabuf(pages)) {
1921: rc = iopt_dmabuf_track_all_domains(area, pages);
1922: if (rc)
1923: goto out_unlock;
1924: }
1925:
1926: if (!iopt_dmabuf_revoked(pages)) {
1927: rc = pfn_reader_first(&pfns, pages, iopt_area_index(area),
1928: iopt_area_last_index(area));
1929: if (rc)
1930: goto out_untrack;
1931:
1932: while (!pfn_reader_done(&pfns)) {
1933: done_first_end_index = pfns.batch_end_index;
1934: done_all_end_index = pfns.batch_start_index;
1935: xa_for_each(&area->iopt->domains, index, domain) {
1936: rc = batch_to_domain(&pfns.batch, domain, area,
1937: pfns.batch_start_index);
1938: if (rc)
1939: goto out_unmap;
1940: }
1941: done_all_end_index = done_first_end_index;
1942:
1943: rc = pfn_reader_next(&pfns);
1944: if (rc)
1945: goto out_unmap;
1946: }
1947: rc = pfn_reader_update_pinned(&pfns);
1948: if (rc)
1949: goto out_unmap;
1950:
1951: pfn_reader_destroy(&pfns);
1952: }
1953:
1954: area->storage_domain = xa_load(&area->iopt->domains, 0);
1955: interval_tree_insert(&area->pages_node, &pages->domains_itree);
1956: mutex_unlock(&pages->mutex);
1957: return 0;
1958:
1959: out_unmap:
1960: pfn_reader_release_pins(&pfns);
1961: xa_for_each(&area->iopt->domains, unmap_index, domain) {
1962: unsigned long end_index;
1963:
1964: if (unmap_index < index)
1965: end_index = done_first_end_index;
1966: else
1967: end_index = done_all_end_index;
1968:
1969: /*
1970: * The area is not yet part of the domains_itree so we have to
1971: * manage the unpinning specially. The last domain does the
1972: * unpin, every other domain is just unmapped.
1973: */
1974: if (unmap_index != area->iopt->next_domain_id - 1) {
1975: if (end_index != iopt_area_index(area))
1976: iopt_area_unmap_domain_range(
1977: area, domain, iopt_area_index(area),
1978: end_index - 1);
1979: } else {
1980: iopt_area_unfill_partial_domain(area, pages, domain,
1981: end_index);
1982: }
1983: }
1984: pfn_reader_destroy(&pfns);
1985: out_untrack:
1986: if (iopt_is_dmabuf(pages))
1987: iopt_dmabuf_untrack_all_domains(area, pages);
1988: out_unlock:
1989: mutex_unlock(&pages->mutex);
1990: return rc;
1991: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 52/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 45506
output: 24
thoughts: 34
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the code:
**Diving into the Function Call Chain**
Alright, hang on a second. I'm looking at `iopt_area_fill_domains`, and it's calling `pfn_reader_first`. That's interesting, I need to know why. Let me quickly jump into the `pfn_reader_first` function to get a handle on what's going on there. I need to understand this immediate call and how it fits into the larger scope of this routine. This looks like a promising avenue of investigation.
|
| 53/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:pfn_reader_first]
Results: map[SourceCode:1343: static int pfn_reader_first(struct pfn_reader *pfns, struct iopt_pages *pages,
1344: unsigned long start_index, unsigned long last_index)
1345: {
1346: int rc;
1347:
1348: if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
1349: WARN_ON(last_index < start_index))
1350: return -EINVAL;
1351:
1352: rc = pfn_reader_init(pfns, pages, start_index, last_index);
1353: if (rc)
1354: return rc;
1355: rc = pfn_reader_next(pfns);
1356: if (rc) {
1357: pfn_reader_destroy(pfns);
1358: return rc;
1359: }
1360: return 0;
1361: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 54/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 46010
output: 24
thoughts: 12
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Checking `pfn_reader_next`**
Alright, time to get my hands dirty. I need to take a look at `pfn_reader_next`. No need for a lengthy preamble – my initial thought process is to dive straight into the function itself. Given the name, I'm expecting this to be a core component of whatever reading mechanism we're dealing with, likely related to processing packet flow notifications (PFNs) or a similar datastream. It's the "next" function, so I'm immediately interested in how it handles iteration or state management within a read loop. Is it thread-safe? Does it handle potential errors gracefully, like EOF or malformed packets? Are there any obvious performance bottlenecks in its design? I need to understand how this ties into the overall data flow – where does the data come from that it reads, and where does it go afterwards? A careful examination of this function will quickly reveal its underlying logic and efficiency. I'll need to scrutinize how it handles the underlying data structures it manipulates.
|
| 55/2 |
2026/08/22 15:18 |
tool |
codesearch-definition-source |
0m
Args: map[Name:pfn_reader_next]
Results: map[SourceCode:1234: static int pfn_reader_next(struct pfn_reader *pfns)
1235: {
1236: int rc;
1237:
1238: batch_clear(&pfns->batch);
1239: pfns->batch_start_index = pfns->batch_end_index;
1240:
1241: while (pfns->batch_end_index != pfns->last_index + 1) {
1242: unsigned int npfns = pfns->batch.total_pfns;
1243:
1244: if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
1245: WARN_ON(interval_tree_double_span_iter_done(&pfns->span)))
1246: return -EINVAL;
1247:
1248: rc = pfn_reader_fill_span(pfns);
1249: if (rc)
1250: return rc;
1251:
1252: if (WARN_ON(!pfns->batch.total_pfns))
1253: return -EINVAL;
1254:
1255: pfns->batch_end_index =
1256: pfns->batch_start_index + pfns->batch.total_pfns;
1257: if (pfns->batch_end_index == pfns->span.last_used + 1)
1258: interval_tree_double_span_iter_next(&pfns->span);
1259:
1260: /* Batch is full */
1261: if (npfns == pfns->batch.total_pfns)
1262: return 0;
1263: }
1264: return 0;
1265: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 56/2 |
2026/08/22 15:18 |
llm |
expert |
0m
Model:
Tokens:
input: 46816
output: 26
thoughts: 14
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Diving into `pfn_reader_fill_span`**
Alright, time to dig into `pfn_reader_fill_span`. I need to refresh my memory on what that function is supposed to be doing, and how it interacts with the broader architecture. I want to check for potential areas of concern, maybe bottlenecks, or anything that might be introducing inefficiencies. Is it handling memory correctly? Are we potentially making unnecessary copies or allocations within that span fill? Does it use the cache efficiently? Let's quickly review the input parameters and return values to confirm my understanding is correct. This is the heart of reading in data, so I need to make sure this portion is running as efficiently as it can. I'm especially interested in the edge cases – are there any boundary conditions or unusual data patterns that could expose vulnerabilities or performance issues? I want to make sure the assumptions built into this code are still valid, particularly in light of recent changes. Finally, I'll consider how this function would impact other sections of the system.
|
| 57/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args: map[Name:pfn_reader_fill_span]
Results: map[SourceCode:1167: /* Process a single span to load it from the proper storage */
1168: static int pfn_reader_fill_span(struct pfn_reader *pfns)
1169: {
1170: struct interval_tree_double_span_iter *span = &pfns->span;
1171: unsigned long start_index = pfns->batch_end_index;
1172: struct pfn_reader_user *user;
1173: unsigned long npages;
1174: struct iopt_area *area;
1175: int rc;
1176:
1177: if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
1178: WARN_ON(span->last_used < start_index))
1179: return -EINVAL;
1180:
1181: if (span->is_used == 1) {
1182: batch_from_xarray(&pfns->batch, &pfns->pages->pinned_pfns,
1183: start_index, span->last_used);
1184: return 0;
1185: }
1186:
1187: if (span->is_used == 2) {
1188: /*
1189: * Pull as many pages from the first domain we find in the
1190: * target span. If it is too small then we will be called again
1191: * and we'll find another area.
1192: */
1193: area = iopt_pages_find_domain_area(pfns->pages, start_index);
1194: if (WARN_ON(!area))
1195: return -EINVAL;
1196:
1197: /* The storage_domain cannot change without the pages mutex */
1198: batch_from_domain(
1199: &pfns->batch, area->storage_domain, area, start_index,
1200: min(iopt_area_last_index(area), span->last_used));
1201: return 0;
1202: }
1203:
1204: if (iopt_is_dmabuf(pfns->pages))
1205: return pfn_reader_fill_dmabuf(&pfns->dmabuf, &pfns->batch,
1206: start_index, span->last_hole);
1207:
1208: user = &pfns->user;
1209: if (start_index >= user->upages_end) {
1210: rc = pfn_reader_user_pin(user, pfns->pages, start_index,
1211: span->last_hole);
1212: if (rc)
1213: return rc;
1214: }
1215:
1216: npages = user->upages_end - start_index;
1217: start_index -= user->upages_start;
1218: rc = 0;
1219:
1220: if (!user->file)
1221: batch_from_pages(&pfns->batch, user->upages + start_index,
1222: npages);
1223: else
1224: rc = batch_from_folios(&pfns->batch, &user->ufolios_next,
1225: &user->ufolios_offset, npages);
1226: return rc;
1227: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 58/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 48090
output: 26
thoughts: 79
Thoughts: Here's my thought process, as I delve into this code snippet:
**Diving into `pfn_reader_fill_span`**
Okay, so I'm looking at `pfn_reader_fill_span` and the first thing that jumps out is that it's checking `if (iopt_is_dmabuf(pfns->pages))`. That's a key initial condition, suggesting DMA buffer handling is involved. Then, immediately after, it checks `if (!user->file)`. This is interesting; why would the presence or absence of a `user->file` be relevant *after* we've possibly identified DMA buffer usage? It's a conditional branch that needs closer scrutiny.
My next step is clear: I need to trace where this `user->file` is set, and how it is involved in the overall PFN reading process. That means going directly to the definition and usage of `pfn_reader_user_pin`. That function is probably where the `user->file` is initialized, or cleared, or used to indicate a state. The interaction between the conditions in `pfn_reader_fill_span` and the initialization of `user->file` in `pfn_reader_user_pin` holds the key to the logic here.
|
| 59/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args: map[Name:pfn_reader_user_pin]
Results: map[SourceCode: 876: static int pfn_reader_user_pin(struct pfn_reader_user *user,
877: struct iopt_pages *pages,
878: unsigned long start_index,
879: unsigned long last_index)
880: {
881: bool remote_mm = pages->source_mm != current->mm;
882: unsigned long npages = last_index - start_index + 1;
883: unsigned long start;
884: unsigned long unum;
885: uintptr_t uptr;
886: long rc;
887:
888: if (IS_ENABLED(CONFIG_IOMMUFD_TEST) &&
889: WARN_ON(last_index < start_index))
890: return -EINVAL;
891:
892: if (!user->file && !user->upages) {
893: /* All undone in pfn_reader_destroy() */
894: user->upages_len = npages * sizeof(*user->upages);
895: user->upages = temp_kmalloc(&user->upages_len, NULL, 0);
896: if (!user->upages)
897: return -ENOMEM;
898: }
899:
900: if (user->file && !user->ufolios) {
901: user->ufolios_len = npages * sizeof(*user->ufolios);
902: user->ufolios = temp_kmalloc(&user->ufolios_len, NULL, 0);
903: if (!user->ufolios)
904: return -ENOMEM;
905: }
906:
907: if (user->locked == -1) {
908: /*
909: * The majority of usages will run the map task within the mm
910: * providing the pages, so we can optimize into
911: * get_user_pages_fast()
912: */
913: if (!user->file && remote_mm) {
914: if (!mmget_not_zero(pages->source_mm))
915: return -EFAULT;
916: }
917: user->locked = 0;
918: }
919:
920: unum = user->file ? user->ufolios_len / sizeof(*user->ufolios) :
921: user->upages_len / sizeof(*user->upages);
922: npages = min_t(unsigned long, npages, unum);
923:
924: if (iommufd_should_fail())
925: return -EFAULT;
926:
927: if (user->file) {
928: start = pages->start + (start_index * PAGE_SIZE);
929: rc = pin_memfd_pages(user, start, npages);
930: } else if (!remote_mm) {
931: uptr = (uintptr_t)(pages->uptr + start_index * PAGE_SIZE);
932: rc = pin_user_pages_fast(uptr, npages, user->gup_flags,
933: user->upages);
934: } else {
935: uptr = (uintptr_t)(pages->uptr + start_index * PAGE_SIZE);
936: if (!user->locked) {
937: mmap_read_lock(pages->source_mm);
938: user->locked = 1;
939: }
940: rc = pin_user_pages_remote(pages->source_mm, uptr, npages,
941: user->gup_flags, user->upages,
942: &user->locked);
943: }
944: if (rc <= 0) {
945: if (WARN_ON(!rc))
946: return -EFAULT;
947: return rc;
948: }
949: iopt_pages_add_npinned(pages, rc);
950: user->upages_start = start_index;
951: user->upages_end = start_index + rc;
952: return 0;
953: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 60/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 49747
output: 24
thoughts: 43
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing:
**Pinpointing the Memory Leak**
Right, hang on a second. I'm following the code path, and I've just noticed something potentially significant. The `pfn_reader_user_pin` function... ah, that's interesting. It looks like it's calling `pin_memfd_pages` if the `user->file` pointer is actually pointing to a file. That's a good clue. I need to understand that. Let me quickly refresh my memory of `pin_memfd_pages`. Let's see what that function is doing in detail and whether it plays a part in the issue at hand.
|
| 61/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args: map[Name:pin_memfd_pages]
Results: map[SourceCode: 824: static long pin_memfd_pages(struct pfn_reader_user *user, unsigned long start,
825: unsigned long npages)
826: {
827: unsigned long i;
828: unsigned long offset;
829: unsigned long npages_out = 0;
830: struct page **upages = user->upages;
831: unsigned long end = start + (npages << PAGE_SHIFT) - 1;
832: long nfolios = user->ufolios_len / sizeof(*user->ufolios);
833:
834: /*
835: * todo: memfd_pin_folios should return the last pinned offset so
836: * we can compute npages pinned, and avoid looping over folios here
837: * if upages == NULL.
838: */
839: nfolios = memfd_pin_folios(user->file, start, end, user->ufolios,
840: nfolios, &offset);
841: if (nfolios <= 0)
842: return nfolios;
843:
844: offset >>= PAGE_SHIFT;
845: user->ufolios_next = user->ufolios;
846: user->ufolios_offset = offset;
847:
848: for (i = 0; i < nfolios; i++) {
849: struct folio *folio = user->ufolios[i];
850: unsigned long nr = folio_nr_pages(folio);
851: unsigned long npin = min(nr - offset, npages);
852:
853: npages -= npin;
854: npages_out += npin;
855:
856: if (upages) {
857: if (npin == 1) {
858: *upages++ = folio_page(folio, offset);
859: } else {
860: int rc = folio_add_pins(folio, npin - 1);
861:
862: if (rc)
863: return rc;
864:
865: while (npin--)
866: *upages++ = folio_page(folio, offset++);
867: }
868: }
869:
870: offset = 0;
871: }
872:
873: return npages_out;
874: }
SourceFile:drivers/iommu/iommufd/pages.c]
|
| 62/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 50728
output: 24
thoughts: 32
Thoughts: Here's my thought process, as if I were analyzing that code:
**Diving into Memory Pinning**
Okay, first things first. I see `pin_memfd_pages` called. That name immediately suggests it's involved in pinning memory pages associated with a memory file descriptor. Now, that function's probably key to how this whole pinning mechanism works, which is why I want to understand it. Let's dig deeper and see what `pin_memfd_pages` actually does. Ah, it calls `memfd_pin_folios` - that's interesting. Folios, right? Those are the memory management units. So, `memfd_pin_folios` must be where the actual work of *pinning* these folios (which contain our pages) is happening. Time to check out what that function does. That function call seems important. I'm going to follow the trail.
|
| 63/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args: map[Name:memfd_pin_folios]
Results: map[SourceCode:3415: /**
3416: * memfd_pin_folios() - pin folios associated with a memfd
3417: * @memfd: the memfd whose folios are to be pinned
3418: * @start: the first memfd offset
3419: * @end: the last memfd offset (inclusive)
3420: * @folios: array that receives pointers to the folios pinned
3421: * @max_folios: maximum number of entries in @folios
3422: * @offset: the offset into the first folio
3423: *
3424: * Attempt to pin folios associated with a memfd in the contiguous range
3425: * [start, end]. Given that a memfd is either backed by shmem or hugetlb,
3426: * the folios can either be found in the page cache or need to be allocated
3427: * if necessary. Once the folios are located, they are all pinned via
3428: * FOLL_PIN and @offset is populatedwith the offset into the first folio.
3429: * And, eventually, these pinned folios must be released either using
3430: * unpin_folios() or unpin_folio().
3431: *
3432: * It must be noted that the folios may be pinned for an indefinite amount
3433: * of time. And, in most cases, the duration of time they may stay pinned
3434: * would be controlled by the userspace. This behavior is effectively the
3435: * same as using FOLL_LONGTERM with other GUP APIs.
3436: *
3437: * Returns number of folios pinned, which could be less than @max_folios
3438: * as it depends on the folio sizes that cover the range [start, end].
3439: * If no folios were pinned, it returns -errno.
3440: */
3441: long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
3442: struct folio **folios, unsigned int max_folios,
3443: pgoff_t *offset)
3444: {
3445: unsigned int flags, nr_folios, nr_found;
3446: unsigned int i, pgshift = PAGE_SHIFT;
3447: pgoff_t start_idx, end_idx;
3448: struct folio *folio = NULL;
3449: struct folio_batch fbatch;
3450: struct hstate *h;
3451: long ret = -EINVAL;
3452:
3453: if (start < 0 || start > end || !max_folios)
3454: return -EINVAL;
3455:
3456: if (!memfd)
3457: return -EINVAL;
3458:
3459: if (!shmem_file(memfd) && !is_file_hugepages(memfd))
3460: return -EINVAL;
3461:
3462: if (end >= i_size_read(file_inode(memfd)))
3463: return -EINVAL;
3464:
3465: if (is_file_hugepages(memfd)) {
3466: h = hstate_file(memfd);
3467: pgshift = huge_page_shift(h);
3468: }
3469:
3470: flags = memalloc_pin_save();
3471: do {
3472: nr_folios = 0;
3473: start_idx = start >> pgshift;
3474: end_idx = end >> pgshift;
3475: if (is_file_hugepages(memfd)) {
3476: start_idx <<= huge_page_order(h);
3477: end_idx <<= huge_page_order(h);
3478: }
3479:
3480: folio_batch_init(&fbatch);
3481: while (start_idx <= end_idx && nr_folios < max_folios) {
3482: /*
3483: * In most cases, we should be able to find the folios
3484: * in the page cache. If we cannot find them for some
3485: * reason, we try to allocate them and add them to the
3486: * page cache.
3487: */
3488: nr_found = filemap_get_folios_contig(memfd->f_mapping,
3489: &start_idx,
3490: end_idx,
3491: &fbatch);
3492: if (folio) {
3493: folio_put(folio);
3494: folio = NULL;
3495: }
3496:
3497: for (i = 0; i < nr_found; i++) {
3498: folio = fbatch.folios[i];
3499:
3500: if (try_grab_folio(folio, 1, FOLL_PIN)) {
3501: folio_batch_release(&fbatch);
3502: ret = -EINVAL;
3503: goto err;
3504: }
3505:
3506: if (nr_folios == 0)
3507: *offset = offset_in_folio(folio, start);
3508:
3509: folios[nr_folios] = folio;
3510: if (++nr_folios == max_folios)
3511: break;
3512: }
3513:
3514: folio = NULL;
3515: folio_batch_release(&fbatch);
3516: if (!nr_found) {
3517: folio = memfd_alloc_folio(memfd, start_idx);
3518: if (IS_ERR(folio)) {
3519: ret = PTR_ERR(folio);
3520: if (ret != -EEXIST)
3521: goto err;
3522: folio = NULL;
3523: }
3524: }
3525: }
3526:
3527: ret = check_and_migrate_movable_folios(nr_folios, folios);
3528: } while (ret == -EAGAIN);
3529:
3530: memalloc_pin_restore(flags);
3531: return ret ? ret : nr_folios;
3532: err:
3533: memalloc_pin_restore(flags);
3534: unpin_folios(folios, nr_folios);
3535:
3536: return ret;
3537: }
SourceFile:mm/gup.c]
|
| 64/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 52872
output: 24
thoughts: 2114
Thoughts: **Analysis of the IOMMU File Mapping Memory Leak**
Okay, let's break this down. It seems the core issue lies within the `memfd_pin_folios` function, and how it interacts with IOMMU mappings. Initially, I thought a failed `memfd_pin_folios` call would result in a clean teardown, preventing any leaks. The logic appears to flow from `memfd_pin_folios` down through several functions: `pin_memfd_pages`, `pfn_reader_user_pin`, `pfn_reader_fill_span`, `pfn_reader_next`, `pfn_reader_first`, `iopt_area_fill_domains`, and finally to `iopt_map_pages`. The intention seemed to be that if there's an error at any point, the mapping would be aborted and resources freed via `iopt_abort_area` and `iopt_put_pages`. And, the `pages` are freed via `fput`. So, good! No memory leak.
But, hang on, re-examining the code, specifically within `iopt_map_common` where `iopt_put_pages` is called, it became clear that `elm.pages` is not NULL and therefore *is* cleaned up by the function. It appeared, at first glance, like the failure of `memfd_pin_folios` was a sufficient condition for a safe exit.
Okay, let's back up. Where's the *real* problem? The bug likely happens in `iopt_map_pages`. Digging deeper into `iopt_fill_domains_pages`, the function calls `iopt_area_fill_domains`. And that's where the critical condition arises. The code has this check: `if (xa_empty(&area->iopt->domains)) return 0;`. If no domains are defined, `iopt_area_fill_domains` returns immediately *without* calling `memfd_pin_folios` and without an error! This results in an empty, or *zero*, return code.
This is the vulnerability's entry-point: If `iopt_area_fill_domains` doesn't call `memfd_pin_folios`, then the check that should prevent us from hitting the memfd bug *never happens*. The happy-path code will then proceed. `elm->area->pages = elm->pages` is set, and `elm->pages = NULL`. The data is then mapped, and the `file` reference *is* kept, creating a new reference-count cycle. This also means that `iopt_put_pages` is *never* called, thus never releasing the `file`'s reference to the memfd.
Let's confirm this by analyzing the reproducer. The reproducer opens `/dev/iommu`, calls `IOMMU_IOAS_ALLOC`, and then `IOMMU_IOAS_MAP_FILE`, *without* attaching a domain to the IOMMU. Thus, `xa_empty(&area->iopt->domains)` is indeed TRUE. So the mapping *succeeds* despite the lack of proper pinning, creating the memory leak.
The process closes the `/dev/iommu` file descriptor. The file's reference count *isn't* zero because the `pages->file` keeps a reference to it. The `iommufd_fops_release` function which should destroy the `ioas` object *isn't* called, meaning the IOMMU object is *not* destroyed. This is a perpetual loop: The `pages` point to the file, and the file points back to `pages`, creating a *permanent* reference count loop. The core structure leaking is: `struct file` -> `struct iommufd_ctx` -> `struct iommufd_ioas` -> `struct iopt_pages` -> `struct iopt_area` -> `struct iopt_pages`.
This is a clean, nasty memory leak.
The key is that `/dev/iommu` is *not* cleaned up when the file descriptor is closed. The memory persists, and each iteration leaks several kernel structures.
This has *no* exploit potential beyond a DoS. It's not a use-after-free, or a type confusion. It's a DoS by exhausting memory. And, based on the permissions, this could be exploited by an unprivileged user. A simple loop that repeatedly calls `open`, `IOMMU_IOAS_ALLOC`, and `IOMMU_IOAS_MAP_FILE` will quickly exhaust kernel memory, leading to an OOM condition.
|
| 65/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode: 786: static int __init iommufd_init(void)
787: {
788: int ret;
789:
790: ret = misc_register(&iommu_misc_dev);
791: if (ret)
792: return ret;
793:
794: if (IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER)) {
795: ret = misc_register(&vfio_misc_dev);
796: if (ret)
797: goto err_misc;
798: }
799: ret = iommufd_test_init();
800: if (ret)
801: goto err_vfio_misc;
802: return 0;
803:
804: err_vfio_misc:
805: if (IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER))
806: misc_deregister(&vfio_misc_dev);
807: err_misc:
808: misc_deregister(&iommu_misc_dev);
809: return ret;
810: }
SourceFile:drivers/iommu/iommufd/main.c]
|
| 66/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 56397
output: 25
thoughts: 13
Thoughts: Here's a summary of my thought process:
**Diving into `iommu_misc_dev`**
Okay, time to dig into `iommu_misc_dev`. This is where things get interesting, and potentially complicated. I immediately need to understand the context. What's the specific problem or area I'm investigating that's led me here? I need to quickly recall my knowledge of the kernel architecture around IOMMU management. What specific aspects of the IOMMU subsystem are potentially relevant to whatever I'm troubleshooting or exploring? I know there's a lot packed into the kernel, from the hardware configuration to the DMA mapping and security. This `iommu_misc_dev` likely holds some low-level interface or control mechanism. I need to be thinking about its purpose. Is this a driver, a helper, an entry point? Is it related to the IOMMU's management, initialization, or specific device handling? My goal now is to quickly and efficiently understand the role and functionality of `iommu_misc_dev` within the broader IOMMU system. Let's see what we can find out.
|
| 67/2 |
2026/08/22 15:19 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode: 761: static struct miscdevice iommu_misc_dev = {
762: .minor = MISC_DYNAMIC_MINOR,
763: .name = "iommu",
764: .fops = &iommufd_fops,
765: .nodename = "iommu",
766: .mode = 0660,
767: };
SourceFile:drivers/iommu/iommufd/main.c]
|
| 68/2 |
2026/08/22 15:19 |
llm |
expert |
0m
Model:
Tokens:
input: 56828
output: 29
thoughts: 1564
Thoughts: **Analyzing the IOMMU Memory Leak Bug**
Okay, so I'm looking at this `IOMMU_IOAS_MAP_FILE` issue. The mode of `/dev/iommu` is `0660`, which immediately tells me it's readable and writable by the owner and group, but not typically accessible to just *any* user. Usually, the owner is `root`, and the group is either `root` or something specific like `kvm` or `iommu`. So, a completely unprivileged user is probably blocked from accessing this, unless they're in the right group.
But wait, considering the bug report mentions `syz.0.25` running as an unprivileged user. That's a good point, I need to consider that it might be in a user namespace, or it might have some special groups. But, access to `/dev/iommu` inside a user namespace isn't automatic; those device nodes aren't exposed unless specifically bind-mounted, or the user has appropriate UID/GID mappings. So, unless Syzkaller is doing something unusual with sandboxing, it wouldn't have direct access. And, the prompt explicitly states that we're looking for a bug accessible to a typical, unprivileged user without any special capabilities. Given the `0660` permissions on `/dev/iommu`, that looks unlikely.
So, `/dev/iommu` is effectively restricted to root, right? Unless udev has changed the group to `kvm` or `vfio`, which can happen. Console users might get access through ACLs, for example. But, strictly speaking, it's a device node designed for root or specific groups.
The key here is whether there's some other way to reach this. What if we use a `memfd`? Let's say, I create a `memfd` and then map that into the IOMMU. The flow is: `memfd` is created, then it becomes `fd`, and `IOMMU_IOAS_MAP_FILE` uses the `fd` (memfd). The code then gets the memfd `file`, allocates pages and sets `pages->file = memfd_file`. This gets mapped into the `ioas`. Okay, now, when I close the `memfd`, the reference count goes down, but it's still held by `pages->file`. So it's still there.
Here's the critical point. This isn't a circular reference! The `ioas` holds the `memfd`. Then, when I close the `iommu_fd`, the `ioas` gets destroyed, which destroys the `iopt`. The `iopt` unmaps the area and frees the `pages`. The pages then drop the reference to the memfd. Therefore, the memfd is freed. So, there is NO memory leak if we are using a memfd!
Ah, right, now I see it. The memory leak *only* happens if I pass the `iommu_fd` *itself* as the file descriptor! That creates a cycle: `iommu_fd` -> `ioas` -> `pages` -> `iommu_fd`. The same object! So, to trigger this, I *must* have access to `/dev/iommu` in the first place, because I need the `iommu_fd`! If I can't open the device, I can't even issue the `ioctl`, so I can't trigger the bug.
Therefore, is this exploitable? No, it's just a memory leak. Is it a Denial of Service? Yes, a memory leak can lead to OOM conditions. Is this accessible to unprivileged processes? No, it requires access to `/dev/iommu`, which is `0660` root:root. Is it accessible via user namespaces? No, user namespaces don't automatically grant access. VM guest, VM host, network trigger? No. Peripheral or malicious filesystem triggers? No.
Wait. Is there any other file we can pass that creates the cycle? What about an `epoll` file descriptor that monitors the `iommu_fd`? `epoll` *holds* a reference to the `iommu_fd`. If I map that `epoll_fd` into the `iommu_fd`, I get: `iommu_fd` -> `ioas` -> `pages` -> `epoll_fd` -> `iommu_fd`. Boom! A cycle! But, wait, an `epoll_fd` is not a memfd or hugetlbfs file. I see, if I attach a domain to the `ioas`, `iopt_area_
|
| 69/2 |
2026/08/22 15:20 |
tool |
grepper |
0m
Args: map[Expression:iommufd PathPrefix:drivers/vfio/]
Results: map[Output:
Full output is too long, showing 500 out of 777 lines.
Use more precise expression if possible.
drivers/vfio/Kconfig=17=config VFIO_DEVICE_CDEV
--
drivers/vfio/Kconfig-23- access. Userspace gets device fd by opening device cdev under
drivers/vfio/Kconfig:24: /dev/vfio/devices/vfioX, and then bind the device fd with an iommufd
drivers/vfio/Kconfig-25- to set up secure DMA context for device access.
--
drivers/vfio/Makefile=6=vfio-$(CONFIG_VFIO_GROUP) += group.o
drivers/vfio/Makefile:7:vfio-$(CONFIG_IOMMUFD) += iommufd.o
drivers/vfio/Makefile-8-vfio-$(CONFIG_VFIO_CONTAINER) += container.o
--
drivers/vfio/cdx/main.c=291=static const struct vfio_device_ops vfio_cdx_ops = {
--
drivers/vfio/cdx/main.c-300- .mmap = vfio_cdx_mmap,
drivers/vfio/cdx/main.c:301: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/cdx/main.c:302: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/cdx/main.c:303: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/cdx/main.c-304-};
--
drivers/vfio/device_cdev.c-5-#include <linux/vfio.h>
drivers/vfio/device_cdev.c:6:#include <linux/iommufd.h>
drivers/vfio/device_cdev.c-7-
--
drivers/vfio/device_cdev.c=72=static int vfio_df_check_token(struct vfio_device *device,
drivers/vfio/device_cdev.c:73: const struct vfio_device_bind_iommufd *bind)
drivers/vfio/device_cdev.c-74-{
--
drivers/vfio/device_cdev.c-91-
drivers/vfio/device_cdev.c:92:long vfio_df_ioctl_bind_iommufd(struct vfio_device_file *df,
drivers/vfio/device_cdev.c:93: struct vfio_device_bind_iommufd __user *arg)
drivers/vfio/device_cdev.c-94-{
--
drivers/vfio/device_cdev.c-96- struct vfio_device *device = df->device;
drivers/vfio/device_cdev.c:97: struct vfio_device_bind_iommufd bind;
drivers/vfio/device_cdev.c-98- unsigned long minsz;
--
drivers/vfio/device_cdev.c-103-
drivers/vfio/device_cdev.c:104: minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
drivers/vfio/device_cdev.c-105-
--
drivers/vfio/device_cdev.c-114-
drivers/vfio/device_cdev.c:115: if (bind.iommufd < 0 || bind.flags & ~VALID_FLAGS)
drivers/vfio/device_cdev.c-116- return -EINVAL;
--
drivers/vfio/device_cdev.c-136-
drivers/vfio/device_cdev.c:137: df->iommufd = iommufd_ctx_from_fd(bind.iommufd);
drivers/vfio/device_cdev.c:138: if (IS_ERR(df->iommufd)) {
drivers/vfio/device_cdev.c:139: ret = PTR_ERR(df->iommufd);
drivers/vfio/device_cdev.c:140: df->iommufd = NULL;
drivers/vfio/device_cdev.c-141- goto out_unlock;
--
drivers/vfio/device_cdev.c-173- vfio_device_put_kvm(device);
drivers/vfio/device_cdev.c:174: iommufd_ctx_put(df->iommufd);
drivers/vfio/device_cdev.c:175: df->iommufd = NULL;
drivers/vfio/device_cdev.c-176-out_unlock:
--
drivers/vfio/device_cdev.c-181-
drivers/vfio/device_cdev.c:182:void vfio_df_unbind_iommufd(struct vfio_device_file *df)
drivers/vfio/device_cdev.c-183-{
--
drivers/vfio/device_cdev.c-196- vfio_device_put_kvm(device);
drivers/vfio/device_cdev.c:197: iommufd_ctx_put(df->iommufd);
drivers/vfio/device_cdev.c-198- device->cdev_opened = false;
--
drivers/vfio/device_cdev.c=203=int vfio_df_ioctl_attach_pt(struct vfio_device_file *df,
drivers/vfio/device_cdev.c:204: struct vfio_device_attach_iommufd_pt __user *arg)
drivers/vfio/device_cdev.c-205-{
drivers/vfio/device_cdev.c:206: struct vfio_device_attach_iommufd_pt attach;
drivers/vfio/device_cdev.c-207- struct vfio_device *device = df->device;
--
drivers/vfio/device_cdev.c-210-
drivers/vfio/device_cdev.c:211: minsz = offsetofend(struct vfio_device_attach_iommufd_pt, pt_id);
drivers/vfio/device_cdev.c-212-
--
drivers/vfio/device_cdev.c-224- return -EOPNOTSUPP;
drivers/vfio/device_cdev.c:225: xend = offsetofend(struct vfio_device_attach_iommufd_pt, pasid);
drivers/vfio/device_cdev.c-226- }
--
drivers/vfio/device_cdev.c=262=int vfio_df_ioctl_detach_pt(struct vfio_device_file *df,
drivers/vfio/device_cdev.c:263: struct vfio_device_detach_iommufd_pt __user *arg)
drivers/vfio/device_cdev.c-264-{
drivers/vfio/device_cdev.c:265: struct vfio_device_detach_iommufd_pt detach;
drivers/vfio/device_cdev.c-266- struct vfio_device *device = df->device;
--
drivers/vfio/device_cdev.c-268-
drivers/vfio/device_cdev.c:269: minsz = offsetofend(struct vfio_device_detach_iommufd_pt, flags);
drivers/vfio/device_cdev.c-270-
--
drivers/vfio/device_cdev.c-282- return -EOPNOTSUPP;
drivers/vfio/device_cdev.c:283: xend = offsetofend(struct vfio_device_detach_iommufd_pt, pasid);
drivers/vfio/device_cdev.c-284- }
--
drivers/vfio/fsl-mc/vfio_fsl_mc.c=575=static const struct vfio_device_ops vfio_fsl_mc_ops = {
--
drivers/vfio/fsl-mc/vfio_fsl_mc.c-585- .mmap = vfio_fsl_mc_mmap,
drivers/vfio/fsl-mc/vfio_fsl_mc.c:586: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/fsl-mc/vfio_fsl_mc.c:587: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/fsl-mc/vfio_fsl_mc.c:588: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/fsl-mc/vfio_fsl_mc.c:589: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/fsl-mc/vfio_fsl_mc.c-590-};
--
drivers/vfio/group.c-13-#include <linux/vfio.h>
drivers/vfio/group.c:14:#include <linux/iommufd.h>
drivers/vfio/group.c-15-#include <linux/anon_inodes.h>
--
drivers/vfio/group.c=63=static bool vfio_group_has_iommu(struct vfio_group *group)
--
drivers/vfio/group.c-71-
drivers/vfio/group.c:72: return group->container || group->iommufd;
drivers/vfio/group.c-73-}
--
drivers/vfio/group.c=81=static int vfio_group_ioctl_unset_container(struct vfio_group *group)
--
drivers/vfio/group.c-96- }
drivers/vfio/group.c:97: if (group->iommufd) {
drivers/vfio/group.c:98: iommufd_ctx_put(group->iommufd);
drivers/vfio/group.c:99: group->iommufd = NULL;
drivers/vfio/group.c-100- }
--
drivers/vfio/group.c=107=static int vfio_group_ioctl_set_container(struct vfio_group *group,
--
drivers/vfio/group.c-110- struct vfio_container *container;
drivers/vfio/group.c:111: struct iommufd_ctx *iommufd;
drivers/vfio/group.c-112- int ret;
--
drivers/vfio/group.c-137-
drivers/vfio/group.c:138: iommufd = iommufd_ctx_from_file(fd_file(f));
drivers/vfio/group.c:139: if (!IS_ERR(iommufd)) {
drivers/vfio/group.c-140- if (IS_ENABLED(CONFIG_VFIO_NOIOMMU) &&
drivers/vfio/group.c-141- group->type == VFIO_NO_IOMMU)
drivers/vfio/group.c:142: ret = iommufd_vfio_compat_set_no_iommu(iommufd);
drivers/vfio/group.c-143- else
drivers/vfio/group.c:144: ret = iommufd_vfio_compat_ioas_create(iommufd);
drivers/vfio/group.c-145-
drivers/vfio/group.c-146- if (ret) {
drivers/vfio/group.c:147: iommufd_ctx_put(iommufd);
drivers/vfio/group.c-148- goto out_unlock;
--
drivers/vfio/group.c-150-
drivers/vfio/group.c:151: group->iommufd = iommufd;
drivers/vfio/group.c-152- goto out_unlock;
--
drivers/vfio/group.c=170=static int vfio_df_group_open(struct vfio_device_file *df)
--
drivers/vfio/group.c-191-
drivers/vfio/group.c:192: df->iommufd = device->group->iommufd;
drivers/vfio/group.c:193: if (df->iommufd && vfio_device_is_noiommu(device) && device->open_count == 0) {
drivers/vfio/group.c-194- /*
--
drivers/vfio/group.c-199- if (!capable(CAP_SYS_RAWIO) ||
drivers/vfio/group.c:200: vfio_iommufd_device_has_compat_ioas(device, df->iommufd)) {
drivers/vfio/group.c-201- ret = -EPERM;
--
drivers/vfio/group.c-209-
drivers/vfio/group.c:210: if (df->iommufd && device->open_count == 1) {
drivers/vfio/group.c:211: ret = vfio_iommufd_compat_attach_ioas(device, df->iommufd);
drivers/vfio/group.c-212- if (ret)
--
drivers/vfio/group.c-228-out_put_kvm:
drivers/vfio/group.c:229: df->iommufd = NULL;
drivers/vfio/group.c-230- if (device->open_count == 0)
--
drivers/vfio/group.c=238=void vfio_df_group_close(struct vfio_device_file *df)
--
drivers/vfio/group.c-245- vfio_df_close(df);
drivers/vfio/group.c:246: df->iommufd = NULL;
drivers/vfio/group.c-247-
--
drivers/vfio/group.c=325=static int vfio_group_ioctl_get_status(struct vfio_group *group,
--
drivers/vfio/group.c-347- * during SET_CONTAINER but for IOMMFD this is done during
drivers/vfio/group.c:348: * VFIO_GROUP_GET_DEVICE_FD. Meaning that with iommufd
drivers/vfio/group.c-349- * VFIO_GROUP_FLAGS_VIABLE could be set but GET_DEVICE_FD will fail due
--
drivers/vfio/group.c=453=static int vfio_group_fops_release(struct inode *inode, struct file *filep)
--
drivers/vfio/group.c-465- vfio_group_detach_container(group);
drivers/vfio/group.c:466: if (group->iommufd) {
drivers/vfio/group.c:467: iommufd_ctx_put(group->iommufd);
drivers/vfio/group.c:468: group->iommufd = NULL;
drivers/vfio/group.c-469- }
--
drivers/vfio/iommufd.c-5-#include <linux/vfio.h>
drivers/vfio/iommufd.c:6:#include <linux/iommufd.h>
drivers/vfio/iommufd.c-7-
--
drivers/vfio/iommufd.c=11=MODULE_IMPORT_NS("IOMMUFD_VFIO");
drivers/vfio/iommufd.c-12-
drivers/vfio/iommufd.c:13:bool vfio_iommufd_device_has_compat_ioas(struct vfio_device *vdev,
drivers/vfio/iommufd.c:14: struct iommufd_ctx *ictx)
drivers/vfio/iommufd.c-15-{
--
drivers/vfio/iommufd.c-17-
drivers/vfio/iommufd.c:18: return !iommufd_vfio_compat_ioas_get_id(ictx, &ioas_id);
drivers/vfio/iommufd.c-19-}
drivers/vfio/iommufd.c-20-
drivers/vfio/iommufd.c:21:int vfio_df_iommufd_bind(struct vfio_device_file *df)
drivers/vfio/iommufd.c-22-{
drivers/vfio/iommufd.c-23- struct vfio_device *vdev = df->device;
drivers/vfio/iommufd.c:24: struct iommufd_ctx *ictx = df->iommufd;
drivers/vfio/iommufd.c-25-
--
drivers/vfio/iommufd.c-27-
drivers/vfio/iommufd.c:28: /* Group noiommu via iommufd compat needs no device binding */
drivers/vfio/iommufd.c-29- if (df->group && vfio_device_is_noiommu(vdev))
--
drivers/vfio/iommufd.c-31-
drivers/vfio/iommufd.c:32: return vdev->ops->bind_iommufd(vdev, ictx, &df->devid);
drivers/vfio/iommufd.c-33-}
drivers/vfio/iommufd.c-34-
drivers/vfio/iommufd.c:35:int vfio_iommufd_compat_attach_ioas(struct vfio_device *vdev,
drivers/vfio/iommufd.c:36: struct iommufd_ctx *ictx)
drivers/vfio/iommufd.c-37-{
--
drivers/vfio/iommufd.c-44- * Compat noiommu does not need to do ioas attach. This helper is
drivers/vfio/iommufd.c:45: * only called from the legacy group/iommufd compat path, so no
drivers/vfio/iommufd.c-46- * explicit df->group check is needed.
--
drivers/vfio/iommufd.c-50-
drivers/vfio/iommufd.c:51: ret = iommufd_vfio_compat_ioas_get_id(ictx, &ioas_id);
drivers/vfio/iommufd.c-52- if (ret)
--
drivers/vfio/iommufd.c-58-
drivers/vfio/iommufd.c:59:void vfio_df_iommufd_unbind(struct vfio_device_file *df)
drivers/vfio/iommufd.c-60-{
--
drivers/vfio/iommufd.c-67-
drivers/vfio/iommufd.c:68: if (vdev->ops->unbind_iommufd)
drivers/vfio/iommufd.c:69: vdev->ops->unbind_iommufd(vdev);
drivers/vfio/iommufd.c-70-}
drivers/vfio/iommufd.c-71-
drivers/vfio/iommufd.c:72:struct iommufd_ctx *vfio_iommufd_device_ictx(struct vfio_device *vdev)
drivers/vfio/iommufd.c-73-{
drivers/vfio/iommufd.c:74: if (vdev->iommufd_device)
drivers/vfio/iommufd.c:75: return iommufd_device_to_ictx(vdev->iommufd_device);
drivers/vfio/iommufd.c-76- return NULL;
drivers/vfio/iommufd.c-77-}
drivers/vfio/iommufd.c:78:EXPORT_SYMBOL_GPL(vfio_iommufd_device_ictx);
drivers/vfio/iommufd.c-79-
drivers/vfio/iommufd.c:80:static int vfio_iommufd_device_id(struct vfio_device *vdev)
drivers/vfio/iommufd.c-81-{
drivers/vfio/iommufd.c:82: if (vdev->iommufd_device)
drivers/vfio/iommufd.c:83: return iommufd_device_to_id(vdev->iommufd_device);
drivers/vfio/iommufd.c-84- return -EINVAL;
--
drivers/vfio/iommufd.c-92- */
drivers/vfio/iommufd.c:93:int vfio_iommufd_get_dev_id(struct vfio_device *vdev, struct iommufd_ctx *ictx)
drivers/vfio/iommufd.c-94-{
--
drivers/vfio/iommufd.c-97-
drivers/vfio/iommufd.c:98: if (vfio_iommufd_device_ictx(vdev) == ictx)
drivers/vfio/iommufd.c:99: return vfio_iommufd_device_id(vdev);
drivers/vfio/iommufd.c-100-
--
drivers/vfio/iommufd.c-104-
drivers/vfio/iommufd.c:105: if (iommufd_ctx_has_group(ictx, group))
drivers/vfio/iommufd.c-106- devid = -ENOENT;
--
drivers/vfio/iommufd.c-113-}
drivers/vfio/iommufd.c:114:EXPORT_SYMBOL_GPL(vfio_iommufd_get_dev_id);
drivers/vfio/iommufd.c-115-
drivers/vfio/iommufd.c-116-/*
drivers/vfio/iommufd.c:117: * The physical standard ops mean that the iommufd_device is bound to the
drivers/vfio/iommufd.c-118- * physical device vdev->dev that was provided to vfio_init_group_dev(). Drivers
--
drivers/vfio/iommufd.c-120- */
drivers/vfio/iommufd.c:121:int vfio_iommufd_physical_bind(struct vfio_device *vdev,
drivers/vfio/iommufd.c:122: struct iommufd_ctx *ictx, u32 *out_device_id)
drivers/vfio/iommufd.c-123-{
drivers/vfio/iommufd.c:124: struct iommufd_device *idev;
drivers/vfio/iommufd.c-125-
drivers/vfio/iommufd.c:126: idev = iommufd_device_bind(ictx, vdev->dev, out_device_id);
drivers/vfio/iommufd.c-127- if (IS_ERR(idev))
drivers/vfio/iommufd.c-128- return PTR_ERR(idev);
drivers/vfio/iommufd.c:129: vdev->iommufd_device = idev;
drivers/vfio/iommufd.c-130- ida_init(&vdev->pasids);
--
drivers/vfio/iommufd.c-132-}
drivers/vfio/iommufd.c:133:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_bind);
drivers/vfio/iommufd.c-134-
drivers/vfio/iommufd.c:135:void vfio_iommufd_physical_unbind(struct vfio_device *vdev)
drivers/vfio/iommufd.c-136-{
--
drivers/vfio/iommufd.c-141- while ((pasid = ida_find_first(&vdev->pasids)) >= 0) {
drivers/vfio/iommufd.c:142: iommufd_device_detach(vdev->iommufd_device, pasid);
drivers/vfio/iommufd.c-143- ida_free(&vdev->pasids, pasid);
--
drivers/vfio/iommufd.c-145-
drivers/vfio/iommufd.c:146: if (vdev->iommufd_attached) {
drivers/vfio/iommufd.c:147: iommufd_device_detach(vdev->iommufd_device, IOMMU_NO_PASID);
drivers/vfio/iommufd.c:148: vdev->iommufd_attached = false;
drivers/vfio/iommufd.c-149- }
drivers/vfio/iommufd.c:150: iommufd_device_unbind(vdev->iommufd_device);
drivers/vfio/iommufd.c:151: vdev->iommufd_device = NULL;
drivers/vfio/iommufd.c-152-}
drivers/vfio/iommufd.c:153:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_unbind);
drivers/vfio/iommufd.c-154-
drivers/vfio/iommufd.c:155:int vfio_iommufd_physical_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
drivers/vfio/iommufd.c-156-{
--
drivers/vfio/iommufd.c-160-
drivers/vfio/iommufd.c:161: if (WARN_ON(!vdev->iommufd_device))
drivers/vfio/iommufd.c-162- return -EINVAL;
drivers/vfio/iommufd.c-163-
drivers/vfio/iommufd.c:164: if (vdev->iommufd_attached)
drivers/vfio/iommufd.c:165: rc = iommufd_device_replace(vdev->iommufd_device,
drivers/vfio/iommufd.c-166- IOMMU_NO_PASID, pt_id);
drivers/vfio/iommufd.c-167- else
drivers/vfio/iommufd.c:168: rc = iommufd_device_attach(vdev->iommufd_device,
drivers/vfio/iommufd.c-169- IOMMU_NO_PASID, pt_id);
--
drivers/vfio/iommufd.c-171- return rc;
drivers/vfio/iommufd.c:172: vdev->iommufd_attached = true;
drivers/vfio/iommufd.c-173- return 0;
drivers/vfio/iommufd.c-174-}
drivers/vfio/iommufd.c:175:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_attach_ioas);
drivers/vfio/iommufd.c-176-
drivers/vfio/iommufd.c:177:void vfio_iommufd_physical_detach_ioas(struct vfio_device *vdev)
drivers/vfio/iommufd.c-178-{
--
drivers/vfio/iommufd.c-180-
drivers/vfio/iommufd.c:181: if (WARN_ON(!vdev->iommufd_device) || !vdev->iommufd_attached)
drivers/vfio/iommufd.c-182- return;
drivers/vfio/iommufd.c-183-
drivers/vfio/iommufd.c:184: iommufd_device_detach(vdev->iommufd_device, IOMMU_NO_PASID);
drivers/vfio/iommufd.c:185: vdev->iommufd_attached = false;
drivers/vfio/iommufd.c-186-}
drivers/vfio/iommufd.c:187:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_detach_ioas);
drivers/vfio/iommufd.c-188-
drivers/vfio/iommufd.c:189:int vfio_iommufd_physical_pasid_attach_ioas(struct vfio_device *vdev,
drivers/vfio/iommufd.c-190- u32 pasid, u32 *pt_id)
--
drivers/vfio/iommufd.c-195-
drivers/vfio/iommufd.c:196: if (WARN_ON(!vdev->iommufd_device))
drivers/vfio/iommufd.c-197- return -EINVAL;
--
drivers/vfio/iommufd.c-199- if (ida_exists(&vdev->pasids, pasid))
drivers/vfio/iommufd.c:200: return iommufd_device_replace(vdev->iommufd_device,
drivers/vfio/iommufd.c-201- pasid, pt_id);
--
drivers/vfio/iommufd.c-206-
drivers/vfio/iommufd.c:207: rc = iommufd_device_attach(vdev->iommufd_device, pasid, pt_id);
drivers/vfio/iommufd.c-208- if (rc)
--
drivers/vfio/iommufd.c-212-}
drivers/vfio/iommufd.c:213:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_pasid_attach_ioas);
drivers/vfio/iommufd.c-214-
drivers/vfio/iommufd.c:215:void vfio_iommufd_physical_pasid_detach_ioas(struct vfio_device *vdev,
drivers/vfio/iommufd.c-216- u32 pasid)
--
drivers/vfio/iommufd.c-219-
drivers/vfio/iommufd.c:220: if (WARN_ON(!vdev->iommufd_device))
drivers/vfio/iommufd.c-221- return;
--
drivers/vfio/iommufd.c-225-
drivers/vfio/iommufd.c:226: iommufd_device_detach(vdev->iommufd_device, pasid);
drivers/vfio/iommufd.c-227- ida_free(&vdev->pasids, pasid);
drivers/vfio/iommufd.c-228-}
drivers/vfio/iommufd.c:229:EXPORT_SYMBOL_GPL(vfio_iommufd_physical_pasid_detach_ioas);
drivers/vfio/iommufd.c-230-
--
drivers/vfio/iommufd.c=238=static void vfio_emulated_unmap(void *data, unsigned long iova,
--
drivers/vfio/iommufd.c-246-
drivers/vfio/iommufd.c:247:static const struct iommufd_access_ops vfio_user_ops = {
drivers/vfio/iommufd.c-248- .needs_pin_pages = 1,
--
drivers/vfio/iommufd.c-251-
drivers/vfio/iommufd.c:252:int vfio_iommufd_emulated_bind(struct vfio_device *vdev,
drivers/vfio/iommufd.c:253: struct iommufd_ctx *ictx, u32 *out_device_id)
drivers/vfio/iommufd.c-254-{
drivers/vfio/iommufd.c:255: struct iommufd_access *user;
drivers/vfio/iommufd.c-256-
--
drivers/vfio/iommufd.c-258-
drivers/vfio/iommufd.c:259: user = iommufd_access_create(ictx, &vfio_user_ops, vdev, out_device_id);
drivers/vfio/iommufd.c-260- if (IS_ERR(user))
drivers/vfio/iommufd.c-261- return PTR_ERR(user);
drivers/vfio/iommufd.c:262: vdev->iommufd_access = user;
drivers/vfio/iommufd.c-263- return 0;
drivers/vfio/iommufd.c-264-}
drivers/vfio/iommufd.c:265:EXPORT_SYMBOL_GPL(vfio_iommufd_emulated_bind);
drivers/vfio/iommufd.c-266-
drivers/vfio/iommufd.c:267:void vfio_iommufd_emulated_unbind(struct vfio_device *vdev)
drivers/vfio/iommufd.c-268-{
--
drivers/vfio/iommufd.c-270-
drivers/vfio/iommufd.c:271: if (vdev->iommufd_access) {
drivers/vfio/iommufd.c:272: iommufd_access_destroy(vdev->iommufd_access);
drivers/vfio/iommufd.c:273: vdev->iommufd_attached = false;
drivers/vfio/iommufd.c:274: vdev->iommufd_access = NULL;
drivers/vfio/iommufd.c-275- }
drivers/vfio/iommufd.c-276-}
drivers/vfio/iommufd.c:277:EXPORT_SYMBOL_GPL(vfio_iommufd_emulated_unbind);
drivers/vfio/iommufd.c-278-
drivers/vfio/iommufd.c:279:int vfio_iommufd_emulated_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
drivers/vfio/iommufd.c-280-{
--
drivers/vfio/iommufd.c-284-
drivers/vfio/iommufd.c:285: if (vdev->iommufd_attached)
drivers/vfio/iommufd.c:286: rc = iommufd_access_replace(vdev->iommufd_access, *pt_id);
drivers/vfio/iommufd.c-287- else
drivers/vfio/iommufd.c:288: rc = iommufd_access_attach(vdev->iommufd_access, *pt_id);
drivers/vfio/iommufd.c-289- if (rc)
drivers/vfio/iommufd.c-290- return rc;
drivers/vfio/iommufd.c:291: vdev->iommufd_attached = true;
drivers/vfio/iommufd.c-292- return 0;
drivers/vfio/iommufd.c-293-}
drivers/vfio/iommufd.c:294:EXPORT_SYMBOL_GPL(vfio_iommufd_emulated_attach_ioas);
drivers/vfio/iommufd.c-295-
drivers/vfio/iommufd.c:296:void vfio_iommufd_emulated_detach_ioas(struct vfio_device *vdev)
drivers/vfio/iommufd.c-297-{
--
drivers/vfio/iommufd.c-299-
drivers/vfio/iommufd.c:300: if (WARN_ON(!vdev->iommufd_access) ||
drivers/vfio/iommufd.c:301: !vdev->iommufd_attached)
drivers/vfio/iommufd.c-302- return;
drivers/vfio/iommufd.c-303-
drivers/vfio/iommufd.c:304: iommufd_access_detach(vdev->iommufd_access);
drivers/vfio/iommufd.c:305: vdev->iommufd_attached = false;
drivers/vfio/iommufd.c-306-}
drivers/vfio/iommufd.c:307:EXPORT_SYMBOL_GPL(vfio_iommufd_emulated_detach_ioas);
--
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c=1581=static const struct vfio_device_ops hisi_acc_vfio_pci_migrn_ops = {
--
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c-1595- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1596: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1597: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1598: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1599: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c-1600-};
--
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c=1602=static const struct vfio_device_ops hisi_acc_vfio_pci_ops = {
--
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c-1616- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1617: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1618: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1619: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:1620: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c-1621-};
--
drivers/vfio/pci/ism/main.c=335=static const struct vfio_device_ops ism_pci_ops = {
--
drivers/vfio/pci/ism/main.c-348- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/ism/main.c:349: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/ism/main.c:350: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/ism/main.c:351: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/ism/main.c:352: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/ism/main.c-353-};
--
drivers/vfio/pci/mlx5/main.c=1386=static const struct vfio_device_ops mlx5vf_pci_ops = {
--
drivers/vfio/pci/mlx5/main.c-1400- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/mlx5/main.c:1401: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/mlx5/main.c:1402: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/mlx5/main.c:1403: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/mlx5/main.c:1404: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/mlx5/main.c-1405-};
--
drivers/vfio/pci/nvgrace-gpu/main.c=1065=static const struct vfio_device_ops nvgrace_gpu_pci_ops = {
--
drivers/vfio/pci/nvgrace-gpu/main.c-1079- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/nvgrace-gpu/main.c:1080: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/nvgrace-gpu/main.c:1081: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/nvgrace-gpu/main.c:1082: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/nvgrace-gpu/main.c:1083: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/nvgrace-gpu/main.c-1084-};
--
drivers/vfio/pci/nvgrace-gpu/main.c=1090=static const struct vfio_device_ops nvgrace_gpu_pci_core_ops = {
--
drivers/vfio/pci/nvgrace-gpu/main.c-1104- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/nvgrace-gpu/main.c:1105: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/nvgrace-gpu/main.c:1106: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/nvgrace-gpu/main.c:1107: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/nvgrace-gpu/main.c:1108: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/nvgrace-gpu/main.c-1109-};
--
drivers/vfio/pci/pds/vfio_dev.c=191=static const struct vfio_device_ops pds_vfio_ops = {
--
drivers/vfio/pci/pds/vfio_dev.c-205- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/pds/vfio_dev.c:206: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/pds/vfio_dev.c:207: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/pds/vfio_dev.c:208: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/pds/vfio_dev.c:209: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/pds/vfio_dev.c-210-};
--
drivers/vfio/pci/qat/main.c=604=static const struct vfio_device_ops qat_vf_pci_ops = {
--
drivers/vfio/pci/qat/main.c-617- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/qat/main.c:618: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/qat/main.c:619: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/qat/main.c:620: .attach_ioas = vfio_iommufd_physical_attach_ioas,
drivers/vfio/pci/qat/main.c:621: .detach_ioas = vfio_iommufd_physical_detach_ioas,
drivers/vfio/pci/qat/main.c-622-};
--
drivers/vfio/pci/vfio_pci.c=149=static const struct vfio_device_ops vfio_pci_ops = {
--
drivers/vfio/pci/vfio_pci.c-163- .match_token_uuid = vfio_pci_core_match_token_uuid,
drivers/vfio/pci/vfio_pci.c:164: .bind_iommufd = vfio_iommufd_physical_bind,
drivers/vfio/pci/vfio_pci.c:165: .unbind_iommufd = vfio_iommufd_physical_unbind,
drivers/vfio/pci/vfio_pci.c:166: .attach_ioas = vfio_iommufd_physical_attach_ioas,
]
|
| 70/2 |
2026/08/22 15:20 |
llm |
expert |
0m
Model:
Tokens:
input: 71824
output: 27
thoughts: 1196
Thoughts: **Analysis of the VFIO IOMMU Memory Leak Vulnerability**
Okay, let's break this down. VFIO allows binding a device to an `iommufd`, which is how the vulnerability is triggered. But to get an `iommufd`, the userspace must first open `/dev/iommu`, which provides the file descriptor needed for `iommufd_ctx_from_fd`. That's the entry point!
So, the critical dependency is the `/dev/iommu` file descriptor. Since this device node has permissions of `0660` root:root, it's not accessible to unprivileged users by default.
Now, what about user namespaces? Even if the user is mapped to root within a namespace, device nodes aren't accessible unless bind-mounted, and even then, the kernel checks permissions against the *initial* user namespace that created the node. This means a user in a user namespace also can't access `/dev/iommu` without real root privileges.
Therefore, this bug appears to be *inaccessible* from both unprivileged processes and user namespaces.
I'm starting to think this is just a Denial of Service (DoS) vulnerability – a memory leak. Not exploitable for privilege escalation, just a potential memory exhaustion issue.
Let's do a more careful examination. Could a cycle be formed by mapping a different file? What if we map a `dma_buf`? Looking at the code, if `CONFIG_DMA_SHARED_BUFFER` is enabled, then a call to `dma_buf_get(fd)` is made.
If a `dma_buf` is mapped, `iopt_alloc_dmabuf_pages` is invoked, which calls `iopt_alloc_pages` to get a page, and the page holds a reference to the `dma_buf`. The type is set to `IOPT_ADDRESS_DMABUF`.
If the `dma_buf` somehow also references the `iommufd`, then we'd have a cycle. Does any `dma_buf` inherently point back to the `iommufd`?
No, typically not. `dma_buf`s are often exported via DRM or VFIO. But, wait... if VFIO *exports* a `dma_buf`, and that `dma_buf` then references the `iommufd` (via the VFIO device's `df->iommufd` or `vdev->iommufd_device`), *then* we have a cycle! The cycle would be: `iommufd` -> `ioas` -> `pages` -> `dma_buf` -> `vfio_device` -> `iommufd`.
And *yes*, the `dma_buf` mapping *is* supported! This would trigger the memory leak!
But... even with this, we're still stuck with the access restriction. To trigger *this* particular cycle, you *still* need access to VFIO and, critically, the `iommufd`. Both are root-restricted.
Therefore, the conclusion remains:
* Exploitable: No.
* Denial Of Service: Yes.
* Accessible From Unprivileged Processes: No.
* Accessible From User Namespaces: No.
* VM Guest Trigger: No.
* VM Host Trigger in The Confidential Computing Context: No.
* Ethernet Network Trigger: No.
* Other Remote Trigger: No.
* Peripheral Trigger: No.
* Malicious Filesystem Trigger: No.
Hold on... could a malicious USB device somehow trigger this? No, USB devices don't interact directly with `/dev/iommu`. And no, a VM guest cannot open `/dev/iommu` as it's a host device node.
Let's re-evaluate the exploitability. Could this memory leak exhaust memory and crash the system? Yes, an Out-Of-Memory (OOM) condition is possible. Could it be used for information leakage? No. For memory corruption? No. It remains a DoS.
Let's double-check unprivileged access. Is `/dev/iommu` *ever* accessible to unprivileged users? In *some* configurations, it might be accessible to a specific group, like `kvm` or `iommu`. If a user is in that group, they *could* trigger it. However, the initial prompt specifies that this user does *not* have special capabilities or restricted device node access. Since `/dev/iommu` is restricted to root or a specific group, it's *inaccessible* to the typical unprivileged user.
One last thing, is there another
|
| 71/2 |
2026/08/22 15:20 |
tool |
codesearch-definition-source |
0m
Args: map[Name:iommufd_fops_ioctl]
Results: map[SourceCode: 524: static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
525: unsigned long arg)
526: {
527: struct iommufd_ctx *ictx = filp->private_data;
528: const struct iommufd_ioctl_op *op;
529: struct iommufd_ucmd ucmd = {};
530: union ucmd_buffer buf;
531: unsigned int nr;
532: int ret;
533:
534: nr = _IOC_NR(cmd);
535: if (nr < IOMMUFD_CMD_BASE ||
536: (nr - IOMMUFD_CMD_BASE) >= ARRAY_SIZE(iommufd_ioctl_ops))
537: return iommufd_vfio_ioctl(ictx, cmd, arg);
538:
539: ucmd.ictx = ictx;
540: ucmd.ubuffer = (void __user *)arg;
541: ret = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer);
542: if (ret)
543: return ret;
544:
545: op = &iommufd_ioctl_ops[nr - IOMMUFD_CMD_BASE];
546: if (op->ioctl_num != cmd)
547: return -ENOIOCTLCMD;
548: if (ucmd.user_size < op->min_size)
549: return -EINVAL;
550:
551: ucmd.cmd = &buf;
552: ret = copy_struct_from_user(ucmd.cmd, op->size, ucmd.ubuffer,
553: ucmd.user_size);
554: if (ret)
555: return ret;
556: ret = op->execute(&ucmd);
557:
558: if (ucmd.new_obj) {
559: if (ret)
560: iommufd_object_abort_and_destroy(ictx, ucmd.new_obj);
561: else
562: iommufd_object_finalize(ictx, ucmd.new_obj);
563: }
564: return ret;
565: }
SourceFile:drivers/iommu/iommufd/main.c]
|
| 72/2 |
2026/08/22 15:20 |
llm |
expert |
0m
Model:
Tokens:
input: 74790
output: 66
thoughts: 211
Thoughts: **My Analysis and Findings**
Okay, here's what I've got. Everything I've been seeing lines up perfectly with my initial assessment. It looks like we've got a classic memory leak, stemming from a circular reference issue within the IOMMU code, specifically involving the mapping of the `/dev/iommu` file descriptor. The root cause is the use of `IOMMU_IOAS_MAP_FILE` when creating the `ioas` object.
The key is this cyclical relationship: the `ioas` object contains a pointer to the mapped file (let's call it `pages->file`). But, that file, in turn, holds a reference back to the `iommufd_ctx`, and the `iommufd_ctx`, in turn, holds a reference to the `ioas` object. Because of this, the file's `release` function never gets called as the reference count never reaches zero, leading to the leak. The cascading effect includes leaked memory from the `iommufd_ctx`, the `ioas` itself, and even the page table structures associated with this mapping.
This is a pretty straightforward Denial of Service (DoS) vulnerability. By repeatedly triggering this mapping, we can exhaust available memory and cause an Out-Of-Memory (OOM) condition. However, I've confirmed that this isn't exploitable for any kind of privilege escalation or information leakage. It's confined to DoS.
Critically, access to `/dev/iommu` is required to trigger this. That file, as we know, is almost always locked down, restricted to root or a specific group. This means that unprivileged users or those within user namespaces shouldn't be able to reach this. So, while it's a leak, it's not a trivial one.
Alright, I'm ready to set the findings now.
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tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
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llm |
expert |
0m
Model:
Tokens:
input: 75533
output: 507
thoughts: 13
Thoughts: Okay, here's my attempt at summarizing the thought process, as if I were a professional in the field:
**Finalizing the Response**
Alright, the data's been analyzed, the conclusions are drawn. Time to craft the final response. It's not just about conveying the information; it's about doing it effectively. I need to synthesize everything, frame it concisely, and make sure the reasoning is clear, compelling, and avoids any potential misinterpretations. This is where I go from analysis to persuasive communication. The audience needs to see the complete picture and be convinced by the evidence I've put together.
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action |
format-explanation |
0m
Results: map[Explanation:The bug is a memory leak caused by a circular reference when mapping the
`/dev/iommu` file descriptor itself into an `ioas` object using the
`IOMMU_IOAS_MAP_FILE` ioctl.
When `IOMMU_IOAS_MAP_FILE` is called with the file descriptor of `/dev/iommu`,
the kernel calls `iopt_alloc_file_pages()`, which takes a reference to the
`file` struct (`pages->file = get_file(file)`). This `pages` object is then
attached to the `ioas` object's page table (`iopt`).
However, the `ioas` object itself is owned by the `iommufd_ctx`, which is tied
to the `/dev/iommu` file descriptor. This creates a reference cycle:
`file (/dev/iommu)` -> `iommufd_ctx` -> `ioas` -> `iopt_area` -> `iopt_pages` ->
`file (/dev/iommu)`.
When the user process exits or closes the file descriptor, the `file`'s
reference count is decremented but does not reach zero because of the reference
held by `iopt_pages`. As a result, the `iommufd_fops_release()` function is
never called, and the `ioas` object is never destroyed, leading to a permanent
memory leak of the `file`, `iommufd_ctx`, `ioas`, and associated page table
structures.
**Exploitability:**
This is a pure memory leak (resource exhaustion) and does not lead to memory
corruption, use-after-free, or information leaks. It is not exploitable for
privilege escalation.
**Denial of Service:**
An attacker with access to `/dev/iommu` can repeatedly trigger this bug in a
loop to leak kernel memory, eventually causing the system to run out of memory
(OOM) and crash, leading to a Denial of Service.
**Access Restrictions:**
The `/dev/iommu` device node is typically created with `0660` permissions and is
owned by `root:root` (or a specific group like `kvm`). Therefore, it is not
accessible to a typical unprivileged user or from within a user namespace unless
the user has been explicitly granted access to the device node.]
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