| 0/0 |
2026/05/23 10:36 |
flow |
assessment-security |
36m
Results: map[DenialOfService:true Explanation:Based on the crash report and source code analysis, here is the assessment of
the bug:
**Root Cause Analysis:**
The crash occurs in `kasan_byte_accessible` when the kernel tries to acquire a
raw spinlock in `task_blocks_on_rt_mutex`.
Tracing the stack and the faulting address (`0x0000000700000af0`), we can
determine the exact sequence of events:
1. A thread calls `mmap` on a file (likely a block device like `/dev/loop1`),
which eventually calls `vma_link_file`.
2. `vma_link_file` attempts to write-lock the file's mapping semaphore:
`i_mmap_lock_write(mapping)`.
3. On `PREEMPT_RT` kernels, `rw_semaphore` is implemented using `rt_mutex`. The
lock is contended, so the thread enters the slow path (`rt_mutex_slowlock` ->
`task_blocks_on_rt_mutex`).
4. Inside `task_blocks_on_rt_mutex`, the kernel reads the current owner of the
lock (`lock->owner`) to perform priority inheritance: `owner =
rt_mutex_owner(lock);`.
5. It then attempts to lock the owner's `pi_lock`:
`raw_spin_lock(&owner->pi_lock);`.
6. The `raw_spin_lock` implementation (with lockdep enabled) accesses
`owner->pi_lock.dep_map`.
The faulting address is `0x0000000700000af0`. In `struct task_struct`, the
`pi_lock` is located at offset `2776` (`0xad8`), and its `dep_map` is at offset
`24` (`0x18`) within the spinlock.
`0xad8 + 0x18 = 0xaf0`.
This perfectly aligns with the faulting address, meaning the `owner` pointer
read from the `rt_mutex` was exactly `0x0000000700000000`!
Because `0x0000000700000000` is a user-space address, KASAN attempts to validate
it. However, KASAN shadow memory only covers kernel-space addresses. The
calculated shadow address for this user-space pointer is `0xdffffc00e000015e`,
which is a non-canonical address, resulting in the observed General Protection
Fault (GPF).
**Security Impact:**
The fact that `mapping->i_mmap_rwsem.rwbase.rtmutex.owner` contains a
controlled/garbage value (`0x0000000700000000` or `0x0000000700000001`) while
the `mapping` pointer itself is a valid kernel address strongly indicates a
**Use-After-Free (UAF)** or **Out-Of-Bounds (OOB) write** memory corruption. The
`struct address_space` (or the `struct file` pointing to it) was likely freed
and reallocated with user-controlled data before the `mmap` path accessed it.
- **Exploitable:** Yes. Memory corruptions involving core kernel structures like
`struct file` or `struct address_space` are highly exploitable and can lead to
local privilege escalation (LPE).
- **Denial of Service:** Yes. Triggering the bug causes a kernel panic/GPF.
- **Accessible From Unprivileged Processes / User Namespaces:** Yes. The bug is
triggered via standard `mmap` operations and potentially loop device
interactions, which can be reached by unprivileged users (or within user
namespaces where they have the necessary capabilities to configure loop
devices). Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/23 10:36 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/05/23 10:36 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/94adcfb3d097a2b540ea36454d1c582a8ed815f0]
|
| 3/1 |
2026/05/23 10:36 |
action |
kernel-builder |
16m
Results: map[KernelObj:/app/workdir/cache/build/ccd517f00bfb58c9d7a90bec52bbf634ba13ef99]
|
| 4/1 |
2026/05/23 10:52 |
action |
codesearch-prepare |
12m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/23 11:04 |
agent |
expert |
7m
Model:
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true 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 greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly 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 tranfers, that's 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 exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial 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:
loop1: detected capacity change from 0 to 32768
Oops: general protection fault, probably for non-canonical address 0xdffffc00e000015e: 0000 [#1] SMP KASAN PTI
KASAN: probably user-memory-access in range [0x0000000700000af0-0x0000000700000af7]
CPU: 1 UID: 0 PID: 20184 Comm: syz.1.2013 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 79 ff ff ff 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 e9 80 7d fd 08 cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc900040771d8 EFLAGS: 00010002
RAX: dffffc0000000000 RBX: ffffffff8b27d44e RCX: 0000000080000003
RDX: 0000000000000000 RSI: ffffffff8b27d44e RDI: 00000000e000015e
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed10060e6ccc R12: 0000000000000000
R13: 0000000700000af0 R14: 0000000700000af0 R15: 0000000000000001
FS: 00007fb5bad366c0(0000) GS:ffff888126432000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33f1aff8 CR3: 000000005c312000 CR4: 00000000003526f0
Call Trace:
<TASK>
__kasan_check_byte+0x12/0x40 mm/kasan/common.c:573
kasan_check_byte include/linux/kasan.h:402 [inline]
lock_acquire+0x79/0x2e0 kernel/locking/lockdep.c:5842
__raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
task_blocks_on_rt_mutex kernel/locking/rtmutex.c:1265 [inline]
__rt_mutex_slowlock kernel/locking/rtmutex.c:1719 [inline]
__rt_mutex_slowlock_locked+0x1226/0x25c0 kernel/locking/rtmutex.c:1760
rt_mutex_slowlock+0xbd/0x170 kernel/locking/rtmutex.c:1800
__rt_mutex_lock kernel/locking/rtmutex.c:1815 [inline]
rwbase_write_lock+0x14d/0x730 kernel/locking/rwbase_rt.c:244
i_mmap_lock_write include/linux/fs.h:512 [inline]
vma_link_file mm/vma.c:1817 [inline]
__mmap_new_vma mm/vma.c:2555 [inline]
__mmap_region mm/vma.c:2759 [inline]
mmap_region+0x1c27/0x2190 mm/vma.c:2844
do_mmap+0xc2f/0x10c0 mm/mmap.c:559
vm_mmap_pgoff+0x2cc/0x4f0 mm/util.c:581
ksys_mmap_pgoff+0x4e8/0x720 mm/mmap.c:605
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb5bcadc819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb5bad36028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007fb5bcd55fa0 RCX: 00007fb5bcadc819
RDX: 0000000000000002 RSI: 0000000000003000 RDI: 0000200000001000
RBP: 00007fb5bcb72c91 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb5bcd56038 R14: 00007fb5bcd55fa0 R15: 00007ffd4540bd48
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 79 ff ff ff 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 e9 80 7d fd 08 cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc900040771d8 EFLAGS: 00010002
RAX: dffffc0000000000 RBX: ffffffff8b27d44e RCX: 0000000080000003
RDX: 0000000000000000 RSI: ffffffff8b27d44e RDI: 00000000e000015e
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed10060e6ccc R12: 0000000000000000
R13: 0000000700000af0 R14: 0000000700000af0 R15: 0000000000000001
FS: 00007fb5bad366c0(0000) GS:ffff888126432000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33f1aff8 CR3: 000000005c312000 CR4: 00000000003526f0
----------------
Code disassembly (best guess), 4 bytes skipped:
0: 0f 1f 40 00 nopl 0x0(%rax)
4: 90 nop
5: 90 nop
6: 90 nop
7: 90 nop
8: 90 nop
9: 90 nop
a: 90 nop
b: 90 nop
c: 90 nop
d: 90 nop
e: 90 nop
f: 90 nop
10: 90 nop
11: 90 nop
12: 90 nop
13: 90 nop
14: 0f 1f 40 d6 nopl -0x2a(%rax)
18: 48 c1 ef 03 shr $0x3,%rdi
1c: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
23: fc ff df
* 26: 0f b6 04 07 movzbl (%rdi,%rax,1),%eax <-- trapping instruction
2a: 3c 08 cmp $0x8,%al
2c: 0f 92 c0 setb %al
2f: e9 80 7d fd 08 jmp 0x8fd7db4
34: cc int3
35: 66 data16
36: 66 data16
37: 66 data16
38: 66 data16
39: 66 data16
3a: 66 data16
3b: 2e cs
Reply: Based on the crash report and source code analysis, here is the assessment of the bug:
**Root Cause Analysis:**
The crash occurs in `kasan_byte_accessible` when the kernel tries to acquire a raw spinlock in `task_blocks_on_rt_mutex`.
Tracing the stack and the faulting address (`0x0000000700000af0`), we can determine the exact sequence of events:
1. A thread calls `mmap` on a file (likely a block device like `/dev/loop1`), which eventually calls `vma_link_file`.
2. `vma_link_file` attempts to write-lock the file's mapping semaphore: `i_mmap_lock_write(mapping)`.
3. On `PREEMPT_RT` kernels, `rw_semaphore` is implemented using `rt_mutex`. The lock is contended, so the thread enters the slow path (`rt_mutex_slowlock` -> `task_blocks_on_rt_mutex`).
4. Inside `task_blocks_on_rt_mutex`, the kernel reads the current owner of the lock (`lock->owner`) to perform priority inheritance: `owner = rt_mutex_owner(lock);`.
5. It then attempts to lock the owner's `pi_lock`: `raw_spin_lock(&owner->pi_lock);`.
6. The `raw_spin_lock` implementation (with lockdep enabled) accesses `owner->pi_lock.dep_map`.
The faulting address is `0x0000000700000af0`. In `struct task_struct`, the `pi_lock` is located at offset `2776` (`0xad8`), and its `dep_map` is at offset `24` (`0x18`) within the spinlock.
`0xad8 + 0x18 = 0xaf0`.
This perfectly aligns with the faulting address, meaning the `owner` pointer read from the `rt_mutex` was exactly `0x0000000700000000`!
Because `0x0000000700000000` is a user-space address, KASAN attempts to validate it. However, KASAN shadow memory only covers kernel-space addresses. The calculated shadow address for this user-space pointer is `0xdffffc00e000015e`, which is a non-canonical address, resulting in the observed General Protection Fault (GPF).
**Security Impact:**
The fact that `mapping->i_mmap_rwsem.rwbase.rtmutex.owner` contains a controlled/garbage value (`0x0000000700000000` or `0x0000000700000001`) while the `mapping` pointer itself is a valid kernel address strongly indicates a **Use-After-Free (UAF)** or **Out-Of-Bounds (OOB) write** memory corruption. The `struct address_space` (or the `struct file` pointing to it) was likely freed and reallocated with user-controlled data before the `mmap` path accessed it.
- **Exploitable:** Yes. Memory corruptions involving core kernel structures like `struct file` or `struct address_space` are highly exploitable and can lead to local privilege escalation (LPE).
- **Denial of Service:** Yes. Triggering the bug causes a kernel panic/GPF.
- **Accessible From Unprivileged Processes / User Namespaces:** Yes. The bug is triggered via standard `mmap` operations and potentially loop device interactions, which can be reached by unprivileged users (or within user namespaces where they have the necessary capabilities to configure loop devices).
|
| 6/2 |
2026/05/23 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 8634
output: 21
thoughts: 462
Thoughts: **Analyzing a Kernel Crash Report**
Okay, here's what I'm seeing: we've got a kernel bug report, specifically an "Oops: general protection fault." The error mentions a non-canonical address, and, crucial for debugging, the KASAN (Kernel Address Sanitizer) flags a likely user-space memory access. That's immediately telling. KASAN is pointing us toward the crash occurring within `kasan_byte_accessible`, a pretty low-level function related to memory access checking. It looks like the call stack is:
`kasan_byte_accessible` -> `__kasan_check_byte` -> `kasan_check_byte` -> `lock_acquire` -> `__raw_spin_lock` -> `_raw_spin_lock` -> `task_blocks_on_rt_mutex` -> `__rt_mutex_slowlock` -> `__rt_mutex_slowlock_locked` -> `rt_mutex_slowlock` -> `__rt_mutex_lock` -> `rwbase_write_lock` -> `i_mmap_lock_write` -> `vma_link_file` -> `__mmap_new_vma` -> `__mmap_region` -> `mmap_region` -> `do_mmap` -> `vm_mmap_pgoff` -> `ksys_mmap_pgoff` -> `do_syscall_64`.
The real kicker is the address, `0x0000000700000af0`. This is user-space, which makes the whole situation a bit more complex. Since this is in `lock_acquire` and the lock being acquired is an `rt_mutex` or potentially an `rw_semaphore` (given the `rwbase_write_lock` usage with PREEMPT_RT), it is likely to be a read-write semaphore. `i_mmap_lock_write` is trying to lock `mapping->i_mmap_rwsem`. So, `mapping` is likely derived from the KASAN-detected address plus an offset equal to `offsetof(struct address_space, i_mmap_rwsem)`. This suggests that the crash likely involves memory mapping. Time to check the layout of `struct address_space`.
|
| 7/2 |
2026/05/23 11:04 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:host OffsetBits:0 SizeBits:64] map[Name:i_pages OffsetBits:64 SizeBits:1152] map[Name:invalidate_lock OffsetBits:1216 SizeBits:1088] map[Name:gfp_mask OffsetBits:2304 SizeBits:32] map[Name:i_mmap_writable OffsetBits:2336 SizeBits:32] map[Name:i_mmap OffsetBits:2368 SizeBits:128] map[Name:nrpages OffsetBits:2496 SizeBits:64] map[Name:writeback_index OffsetBits:2560 SizeBits:64] map[Name:a_ops OffsetBits:2624 SizeBits:64] map[Name:flags OffsetBits:2688 SizeBits:64] map[Name:wb_err OffsetBits:2752 SizeBits:32] map[Name:i_private_lock OffsetBits:2816 SizeBits:1024] map[Name:i_private_list OffsetBits:3840 SizeBits:128] map[Name:i_mmap_rwsem OffsetBits:3968 SizeBits:1088] map[Name:i_private_data OffsetBits:5056 SizeBits:64]]]
|
| 8/2 |
2026/05/23 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 9978
output: 41
thoughts: 206
Thoughts: **Deconstructing the Memory Map**
Okay, so I'm tracking down this memory map issue. I've pinpointed that `i_mmap_rwsem` resides at an offset of 496 bytes, or 0x1f0, within some structure. Let's say, just for illustration, that `i_mmap_rwsem` is located at memory address `0x0000000700000af0`. Based on that offset, I can deduce that the `mapping` field, presumably a pointer to a `struct vm_area_struct` or similar, is located at `0x0000000700000900`, just by doing some simple address arithmetic.
But here's the kicker: that address is in user-space! This is what's catching my attention. Why is a core data structure related to memory mapping ending up with a user-space address? That's not supposed to happen! This suggests some kind of cross-domain confusion, or a pointer that's been mismanaged. I need to understand the path that led to this address being assigned in user-space.
My immediate thought is, what's calling that `vma_link_file` function? That's the key. I seem to recall that the `vma_link_file` function is called from within `__mmap_new_vma`. Alright, let's refresh my memory, `vma_link_file` is called from `__mmap_new_vma` in `mm/vma.c`, as a quick cross-reference confirms. Now I'll drill into the code and start looking at the implementation of `vma_link_file`, tracing how it is being called from the mm subsystem. This is where I'll find my answer, I'm sure.
|
| 9/2 |
2026/05/23 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:vma_link_file]
Results: map[SourceCode:1810: static void vma_link_file(struct vm_area_struct *vma, bool hold_rmap_lock)
1811: {
1812: struct file *file = vma->vm_file;
1813: struct address_space *mapping;
1814:
1815: if (file) {
1816: mapping = file->f_mapping;
1817: i_mmap_lock_write(mapping);
1818: __vma_link_file(vma, mapping);
1819: if (!hold_rmap_lock)
1820: i_mmap_unlock_write(mapping);
1821: }
1822: }
SourceFile:mm/vma.c]
|
| 10/2 |
2026/05/23 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 10856
output: 19
thoughts: 99
Thoughts: **Investigating a Potentially Corrupted File Mapping**
Okay, so I'm looking at this code and something's not quite right. It looks like `file->f_mapping` is being treated as a user-space address. That immediately raises a red flag. How can `f_mapping`, which should be a kernel structure describing the file's page cache, be a user-space address? This seems fundamentally incorrect.
Wait a second⦠maybe the problem isn't `f_mapping` directly, but the `file` pointer itself. Perhaps `file` has been corrupted, or is pointing to an invalid memory location, potentially a user-space address? If so, then accessing `file->f_mapping` is just leading us further down a rabbit hole.
To get a better handle on this, I need to know the layout of the `struct file`. Let's assume that `file` is at `0x0000000700000900` - `offsetof(struct file, f_mapping)`. I'll cross-reference the offset with the struct definition to confirm this, so I can establish how the structure is layed out in memory and what value to expect in memory at the offset location. I need to be sure. I'll need to double-check that offset and the structure's fields.
|
| 11/2 |
2026/05/23 11:04 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:f_lock OffsetBits:0 SizeBits:1024] map[Name:f_mode OffsetBits:1024 SizeBits:32] map[Name:f_op OffsetBits:1088 SizeBits:64] map[Name:f_mapping OffsetBits:1152 SizeBits:64] map[Name:private_data OffsetBits:1216 SizeBits:64] map[Name:f_inode OffsetBits:1280 SizeBits:64] map[Name:f_flags OffsetBits:1344 SizeBits:32] map[Name:f_iocb_flags OffsetBits:1376 SizeBits:32] map[Name:f_cred OffsetBits:1408 SizeBits:64] map[Name:f_owner OffsetBits:1472 SizeBits:64] map[Name: OffsetBits:1536 SizeBits:128] map[Name: OffsetBits:1664 SizeBits:1024] map[Name:f_pos OffsetBits:2688 SizeBits:64] map[Name:f_security OffsetBits:2752 SizeBits:64] map[Name:f_wb_err OffsetBits:2816 SizeBits:32] map[Name:f_sb_err OffsetBits:2848 SizeBits:32] map[Name:f_ep OffsetBits:2880 SizeBits:64] map[Name: OffsetBits:2944 SizeBits:256] map[Name:f_ref OffsetBits:3200 SizeBits:64]]]
|
| 12/2 |
2026/05/23 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 11697
output: 43
thoughts: 439
Thoughts: **Analyzing the Memory Corruption**
Okay, let's break this down. The crash is happening within `i_mmap_lock_write`, specifically accessing `mapping->i_mmap_rwsem`. The fault address is `0x0000000700000af0`. I need to figure out how `mapping` is being constructed here.
I know that `f_mapping` within a `file` structure is located at an offset of 144 bytes, or `0x90`. If the `file` pointer is `0x0000000700000870`, then the expected value of `file->f_mapping` should be read from `0x0000000700000870 + 0x90`, which calculates out to `0x0000000700000900`.
The fault is occurring when trying to access memory using the calculated `mapping` value `0x0000000700000900`. I can confirm this is correct, because if `mapping` is indeed `0x0000000700000900`, then accessing `mapping->i_mmap_rwsem` (which has an offset of `0x1f0` within the mapping struct) gives us `0x0000000700000900 + 0x1f0 = 0x0000000700000af0`. This matches the fault address perfectly!
So, the value of `mapping` is clearly `0x0000000700000900`. Where is this value coming from? It's derived from `file->f_mapping`. This is where the root cause lies. If `file` was a legitimate kernel pointer, then the value of `file->f_mapping` itself must have been corrupted to point to `0x0000000700000900`.
However, the problem could be much more fundamental. If `file` is itself corrupted, maybe pointing to a user-space address, then the read of `file->f_mapping` would result in a user-space value, which will trigger the crash when accessed later.
Let's assume `file` is corrupted, perhaps to `0x0000000700000870`. Then `file->f_mapping` will be read from user space, and we'd end up with `0x0000000700000900` being the calculated `mapping`.
Now, where did this `file` pointer come from? It's derived from `vma->vm_file`. We need to trace this back. Looks like `vma_link_file` is the likely candidate, being called from `__mmap_new_vma`. This is where I'll focus my attention.
|
| 13/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:__mmap_new_vma]
Results: map[SourceCode:2497: /*
2498: * __mmap_new_vma() - Allocate a new VMA for the region, as merging was not
2499: * possible.
2500: *
2501: * @map: Mapping state.
2502: * @vmap: Output pointer for the new VMA.
2503: *
2504: * Returns: Zero on success, or an error.
2505: */
2506: static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap)
2507: {
2508: struct vma_iterator *vmi = map->vmi;
2509: int error = 0;
2510: struct vm_area_struct *vma;
2511:
2512: /*
2513: * Determine the object being mapped and call the appropriate
2514: * specific mapper. the address has already been validated, but
2515: * not unmapped, but the maps are removed from the list.
2516: */
2517: vma = vm_area_alloc(map->mm);
2518: if (!vma)
2519: return -ENOMEM;
2520:
2521: vma_iter_config(vmi, map->addr, map->end);
2522: vma_set_range(vma, map->addr, map->end, map->pgoff);
2523: vm_flags_init(vma, map->vm_flags);
2524: vma->vm_page_prot = map->page_prot;
2525:
2526: if (vma_iter_prealloc(vmi, vma)) {
2527: error = -ENOMEM;
2528: goto free_vma;
2529: }
2530:
2531: if (map->file)
2532: error = __mmap_new_file_vma(map, vma);
2533: else if (map->vm_flags & VM_SHARED)
2534: error = shmem_zero_setup(vma);
2535: else
2536: vma_set_anonymous(vma);
2537:
2538: if (error)
2539: goto free_iter_vma;
2540:
2541: if (!map->check_ksm_early) {
2542: update_ksm_flags(map);
2543: vm_flags_init(vma, map->vm_flags);
2544: }
2545:
2546: #ifdef CONFIG_SPARC64
2547: /* TODO: Fix SPARC ADI! */
2548: WARN_ON_ONCE(!arch_validate_flags(map->vm_flags));
2549: #endif
2550:
2551: /* Lock the VMA since it is modified after insertion into VMA tree */
2552: vma_start_write(vma);
2553: vma_iter_store_new(vmi, vma);
2554: map->mm->map_count++;
2555: vma_link_file(vma, map->hold_file_rmap_lock);
2556:
2557: /*
2558: * vma_merge_new_range() calls khugepaged_enter_vma() too, the below
2559: * call covers the non-merge case.
2560: */
2561: if (!vma_is_anonymous(vma))
2562: khugepaged_enter_vma(vma, map->vm_flags);
2563: *vmap = vma;
2564: return 0;
2565:
2566: free_iter_vma:
2567: vma_iter_free(vmi);
2568: free_vma:
2569: vm_area_free(vma);
2570: return error;
2571: }
SourceFile:mm/vma.c]
|
| 14/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 14033
output: 45
thoughts: 42
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience:
**Analyzing `vma` and File Mapping**
Alright, let's break this down. From my perspective, I'm noting that this newly allocated `vma` structure is fresh on the scene. I immediately link it to the file being mapped β that's the obvious connection. My mental thread here is tracking the allocation of virtual memory space, the `vma`, and its crucial relationship to the underlying file. Now, I'm recalling the function `__mmap_new_file_vma`. That's where it all clicks. *That's* the point where the `vma->vm_file` pointer actually gets assigned. It's the key linkage between the virtual memory region and the on-disk file.
|
| 15/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:__mmap_new_file_vma]
Results: map[SourceCode:2455: static int __mmap_new_file_vma(struct mmap_state *map,
2456: struct vm_area_struct *vma)
2457: {
2458: struct vma_iterator *vmi = map->vmi;
2459: int error;
2460:
2461: vma->vm_file = map->file;
2462: if (!map->file_doesnt_need_get)
2463: get_file(map->file);
2464:
2465: if (!map->file->f_op->mmap)
2466: return 0;
2467:
2468: error = mmap_file(vma->vm_file, vma);
2469: if (error) {
2470: UNMAP_STATE(unmap, vmi, vma, vma->vm_start, vma->vm_end,
2471: map->prev, map->next);
2472: fput(vma->vm_file);
2473: vma->vm_file = NULL;
2474:
2475: vma_iter_set(vmi, vma->vm_end);
2476: /* Undo any partial mapping done by a device driver. */
2477: unmap_region(&unmap);
2478: return error;
2479: }
2480:
2481: /* Drivers cannot alter the address of the VMA. */
2482: WARN_ON_ONCE(map->addr != vma->vm_start);
2483: /*
2484: * Drivers should not permit writability when previously it was
2485: * disallowed.
2486: */
2487: VM_WARN_ON_ONCE(map->vm_flags != vma->vm_flags &&
2488: !(map->vm_flags & VM_MAYWRITE) &&
2489: (vma->vm_flags & VM_MAYWRITE));
2490:
2491: map->file = vma->vm_file;
2492: map->vm_flags = vma->vm_flags;
2493:
2494: return 0;
2495: }
SourceFile:mm/vma.c]
|
| 16/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 14951
output: 24
thoughts: 270
Thoughts: **Analyzing a Kernel Crash During mmap Operations**
Okay, so I'm diving into this kernel crash. My immediate thought is, "Aha! `mmap_file(vma->vm_file, vma)` calls the driver's `mmap` function." This is where things can get hairy. The driver's `mmap` function has the power to mess with `vma->vm_file` itself. That's a red flag. If the driver is malicious, or buggy, and sets `vma->vm_file` to a user-space pointer, or anything that's not a valid `struct file *`, we're heading for trouble.
I see that `map->file = vma->vm_file;` updates `map->file` down the line. Then, `vma_link_file(vma, ...)` is called. And *that's* where the problem likely surfaces. `vma_link_file` reads `file = vma->vm_file; mapping = file->f_mapping;`. If the driver's `mmap` function *did* change `vma->vm_file` to garbage, this is where we'll crash, attempting to dereference an invalid pointer. Bingo.
But wait, I need to figure out *which* driver's `mmap` function is responsible. Let's see... The bug report says "loop1: detected capacity change from 0 to 32768." That's a strong hint. The "loop" device sounds like the prime suspect. So, I need to check if the loop device driver even has an `mmap` function defined. That's my next step. I'm betting that's where the vulnerability lies.
|
| 17/2 |
2026/05/23 11:05 |
tool |
grepper |
0m
Error:
Args: map[Expression:\.mmap.*=.*loop_mmap]
Results:
|
| 18/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 15641
output: 25
thoughts: 15
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Memory Mapping Block Devices: A Flash of Insight**
Alright, let's see... the initial thought process is a bit fragmented, but the key is surfacing now. My brain, as it always does when tackling block device performance, immediately starts considering the low-level interactions. It's a fundamental part of the toolkit. The question of how these devices actually *do* their thing, for memory reads. That's when it hits me: the direct memory access is how `blkdev_mmap`, or something similar, comes into play. I'm thinking direct access of the drive or flash itself. So we're not talking about some standard buffering, but direct memory mapping.
|
| 19/2 |
2026/05/23 11:05 |
tool |
grepper |
0m
Args: map[Expression:\.mmap.*=.*blkdev_mmap]
Results: map[Output:block/fops.c=952=const struct file_operations def_blk_fops = {
--
block/fops.c-958- .iopoll = iocb_bio_iopoll,
block/fops.c:959: .mmap_prepare = blkdev_mmap_prepare,
block/fops.c-960- .fsync = blkdev_fsync,
]
|
| 20/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 15962
output: 41
thoughts: 40
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience, and delivered as a first-person account:
**Navigating the Block Device Mapping Landscape**
Right, let me see... I'm looking at this block device code, and I'm trying to figure out how memory mapping is handled. Okay, so `blkdev_mmap` isn't showing up as a function, which is a bit unusual. But there's a `blkdev_mmap_prepare` function that's around, which *might* be relevant. I need to dig deeper. I'm wondering if mapping is handled differently now. Ah, here we go, let me check the `def_blk_fops` structure⦠Yep, there it is! `mmap` is actually *present* in `def_blk_fops`! So mapping is still supported, just using a different route. So looks like it's the standard file operation. Seems like the kernel has moved to some kind of preparation function to make mapping happen. I need to remember the new naming scheme.
|
| 21/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/fops.c IncludeLines:true Name:def_blk_fops]
Results: map[SourceCode: 952: const struct file_operations def_blk_fops = {
953: .open = blkdev_open,
954: .release = blkdev_release,
955: .llseek = blkdev_llseek,
956: .read_iter = blkdev_read_iter,
957: .write_iter = blkdev_write_iter,
958: .iopoll = iocb_bio_iopoll,
959: .mmap_prepare = blkdev_mmap_prepare,
960: .fsync = blkdev_fsync,
961: .unlocked_ioctl = blkdev_ioctl,
962: #ifdef CONFIG_COMPAT
963: .compat_ioctl = compat_blkdev_ioctl,
964: #endif
965: .splice_read = filemap_splice_read,
966: .splice_write = iter_file_splice_write,
967: .fallocate = blkdev_fallocate,
968: .uring_cmd = blkdev_uring_cmd,
969: .fop_flags = FOP_BUFFER_RASYNC,
970: };
SourceFile:block/fops.c]
|
| 22/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 16655
output: 39
thoughts: 95
Thoughts: **Debugging a File Mapping Issue**
Okay, hold on a second. I was just looking at `def_blk_fops`, and it doesn't seem to define a `.mmap` operation. That's a bit odd. I know `mmap_file` is called during mapping, and it specifically checks if `file->f_op->mmap` is NULL. If it is, `mmap_file` returns 0. That looks like the root of the problem.
Wait, where *is* `mmap_file` used? Ah, right, `__mmap_new_file_vma`. It's all connected. Let me just quickly confirm that `mmap_file` itself is just a wrapper function. I need to understand what's really happening inside it. I need to dive deeper into `mmap_file` and figure out what the underlying function call is and understand its logic.
|
| 23/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:mmap_file]
Results: map[SourceCode: 155: /*
156: * This is a file-backed mapping, and is about to be memory mapped - invoke its
157: * mmap hook and safely handle error conditions. On error, VMA hooks will be
158: * mutated.
159: *
160: * @file: File which backs the mapping.
161: * @vma: VMA which we are mapping.
162: *
163: * Returns: 0 if success, error otherwise.
164: */
165: static inline int mmap_file(struct file *file, struct vm_area_struct *vma)
166: {
167: int err = vfs_mmap(file, vma);
168:
169: if (likely(!err))
170: return 0;
171:
172: /*
173: * OK, we tried to call the file hook for mmap(), but an error
174: * arose. The mapping is in an inconsistent state and we must not invoke
175: * any further hooks on it.
176: */
177: vma->vm_ops = &vma_dummy_vm_ops;
178:
179: return err;
180: }
SourceFile:mm/internal.h]
|
| 24/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 17386
output: 39
thoughts: 23
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the `vfs_mmap` Call**
Right, so `vfs_mmap` is being invoked. My first thought is to immediately dive into the `vfs_mmap` function itself. I need to understand the exact context, the calling arguments, and, most importantly, the *why* behind this particular memory mapping operation. I'm looking for the specific file descriptor, the requested protection flags, the offset, and the length. I want to quickly ascertain what the kernel's doing here: is it a regular file mapping, a shared memory region, or something more exotic like device memory? Is there anything unusual about the parameters that might indicate a potential issue or a specific optimization? My mental checklist includes considering potential interaction with page fault handlers, potential caching strategies, and any possible synchronization requirements if this is a shared mapping. Let's see what we have.
|
| 25/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/internal.h IncludeLines:true Name:vfs_mmap]
Results: map[SourceCode:2065: static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
2066: {
2067: if (file->f_op->mmap_prepare)
2068: return compat_vma_mmap(file, vma);
2069:
2070: return file->f_op->mmap(file, vma);
2071: }
SourceFile:include/linux/fs.h]
|
| 26/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 17797
output: 43
thoughts: 43
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Diving into the `mmap` Implementation**
Right, so I'm tracing through the `mmap` system call implementation and it seems like `vfs_mmap` is the gateway. I've got a strong suspicion that if a `mmap_prepare` hook is defined, it will trigger the use of `compat_vma_mmap`. That's a good lead. Now, my next step is definitely to dig into `compat_vma_mmap`. I need to understand exactly what that function does, what kind of compatibility handling it's performing, and in what specific circumstances it's called. This likely has relevance to how architectures handle memory management differently or how old binaries are supported. I'll need to focus on what the compatibility layer handles for different calling parameters.
|
| 27/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/fs.h IncludeLines:true Name:compat_vma_mmap]
Results: map[SourceCode:1174: /**
1175: * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
1176: * existing VMA and execute any requested actions.
1177: * @file: The file which possesss an f_op->mmap_prepare() hook.
1178: * @vma: The VMA to apply the .mmap_prepare() hook to.
1179: *
1180: * Ordinarily, .mmap_prepare() is invoked directly upon mmap(). However, certain
1181: * stacked filesystems invoke a nested mmap hook of an underlying file.
1182: *
1183: * Until all filesystems are converted to use .mmap_prepare(), we must be
1184: * conservative and continue to invoke these stacked filesystems using the
1185: * deprecated .mmap() hook.
1186: *
1187: * However we have a problem if the underlying file system possesses an
1188: * .mmap_prepare() hook, as we are in a different context when we invoke the
1189: * .mmap() hook, already having a VMA to deal with.
1190: *
1191: * compat_vma_mmap() is a compatibility function that takes VMA state,
1192: * establishes a struct vm_area_desc descriptor, passes to the underlying
1193: * .mmap_prepare() hook and applies any changes performed by it.
1194: *
1195: * Once the conversion of filesystems is complete this function will no longer
1196: * be required and will be removed.
1197: *
1198: * Returns: 0 on success or error.
1199: */
1200: int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
1201: {
1202: return __compat_vma_mmap(file->f_op, file, vma);
1203: }
SourceFile:mm/util.c]
|
| 28/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 18643
output: 42
thoughts: 14
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in kernel internals, specifically memory management, and I'm talking to myself (or maybe just thinking it):
**Checking the Compatibility of vma_mmap**
Right, let's see, let's just make sure we check `__compat_vma_mmap`... I'm assuming we're dealing with something related to compatibility. Likely a system call or memory mapping interaction involving a different architecture's process or a change in the kernel. `vma` is the virtual memory area, so we are probably dealing with mmap in some way. We should really make sure this is the right place and not, say, mmap itself, or something else entirely. We need to be careful to get the correct area for compatibility checks.
|
| 29/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/util.c IncludeLines:true Name:__compat_vma_mmap]
Results: map[SourceCode:1137: /**
1138: * __compat_vma_mmap() - See description for compat_vma_mmap()
1139: * for details. This is the same operation, only with a specific file operations
1140: * struct which may or may not be the same as vma->vm_file->f_op.
1141: * @f_op: The file operations whose .mmap_prepare() hook is specified.
1142: * @file: The file which backs or will back the mapping.
1143: * @vma: The VMA to apply the .mmap_prepare() hook to.
1144: * Returns: 0 on success or error.
1145: */
1146: int __compat_vma_mmap(const struct file_operations *f_op,
1147: struct file *file, struct vm_area_struct *vma)
1148: {
1149: struct vm_area_desc desc = {
1150: .mm = vma->vm_mm,
1151: .file = file,
1152: .start = vma->vm_start,
1153: .end = vma->vm_end,
1154:
1155: .pgoff = vma->vm_pgoff,
1156: .vm_file = vma->vm_file,
1157: .vma_flags = vma->flags,
1158: .page_prot = vma->vm_page_prot,
1159:
1160: .action.type = MMAP_NOTHING, /* Default */
1161: };
1162: int err;
1163:
1164: err = f_op->mmap_prepare(&desc);
1165: if (err)
1166: return err;
1167:
1168: mmap_action_prepare(&desc.action, &desc);
1169: set_vma_from_desc(vma, &desc);
1170: return mmap_action_complete(&desc.action, vma);
1171: }
SourceFile:mm/util.c]
|
| 30/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 19487
output: 42
thoughts: 36
Thoughts: Here's my summary, as if I were thinking these thoughts:
**Analyzing `set_vma_from_desc`**
Okay, so `set_vma_from_desc` is the function we're looking at. The name itself is pretty explicit: it suggests the routine updates a Virtual Memory Area (VMA), leveraging information from a descriptor structure, `desc`. I need to confirm the specifics. Let's dig into the implementation of `set_vma_from_desc` and see precisely how it's manipulating the VMA based on this descriptor. I'm keen to understand how it's applying the `desc` properties.
|
| 31/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/util.c IncludeLines:true Name:set_vma_from_desc]
Results: map[SourceCode: 294: /*
295: * Temporary helper function for stacked mmap handlers which specify
296: * f_op->mmap() but which might have an underlying file system which implements
297: * f_op->mmap_prepare().
298: */
299: static inline void set_vma_from_desc(struct vm_area_struct *vma,
300: struct vm_area_desc *desc)
301: {
302: /*
303: * Since we're invoking .mmap_prepare() despite having a partially
304: * established VMA, we must take care to handle setting fields
305: * correctly.
306: */
307:
308: /* Mutable fields. Populated with initial state. */
309: vma->vm_pgoff = desc->pgoff;
310: if (desc->vm_file != vma->vm_file)
311: vma_set_file(vma, desc->vm_file);
312: vma->flags = desc->vma_flags;
313: vma->vm_page_prot = desc->page_prot;
314:
315: /* User-defined fields. */
316: vma->vm_ops = desc->vm_ops;
317: vma->vm_private_data = desc->private_data;
318: }
SourceFile:mm/vma.h]
|
| 32/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 20136
output: 41
thoughts: 19
Thoughts: Here's my understanding of the thought process, from the perspective of an experienced kernel developer:
**VMA File Association - A Simple Realization**
Okay, so I'm focusing on the Virtual Memory Area (VMA) and how it's linked to a file. It just hit me - `vma_set_file` is the function responsible for associating a file with a VMA. Thatβs pretty straightforward, but sometimes itβs the simple things you overlook when youβre digging deep into the code. This function must handle the crucial connection between the memory mapping and the underlying file. I should have made the leap quicker. It makes total sense β this sets `vma->vm_file`, the crucial link. Now that Iβve got that straight, I can move on to understand *how* it's done and what implications that has.
|
| 33/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.h IncludeLines:true Name:vma_set_file]
Results: map[SourceCode: 325: /*
326: * Change backing file, only valid to use during initial VMA setup.
327: */
328: void vma_set_file(struct vm_area_struct *vma, struct file *file)
329: {
330: /* Changing an anonymous vma with this is illegal */
331: get_file(file);
332: swap(vma->vm_file, file);
333: fput(file);
334: }
SourceFile:mm/util.c]
|
| 34/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 20551
output: 42
thoughts: 31
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating the mmap/blkdev Relationship**
Alright, so I'm seeing that the `desc->vm_file` member is being set within the `mmap_prepare` function. That's the key setup for, well, the memory map. My gut feeling is that this has something to do with block device mmap and how the backing file is established.
Given that, I need to understand what's happening at the `blkdev_mmap_prepare` level. It's the logical next step. It's where the block device interaction is happening at the core level. I need to trace this function as it is the critical point.
|
| 35/2 |
2026/05/23 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/fops.c IncludeLines:true Name:blkdev_mmap_prepare]
Results: map[SourceCode: 942: static int blkdev_mmap_prepare(struct vm_area_desc *desc)
943: {
944: struct file *file = desc->file;
945:
946: if (bdev_read_only(I_BDEV(bdev_file_inode(file))))
947: return generic_file_readonly_mmap_prepare(desc);
948:
949: return generic_file_mmap_prepare(desc);
950: }
SourceFile:block/fops.c]
|
| 36/2 |
2026/05/23 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 20958
output: 43
thoughts: 14
Thoughts: Okay, let's dive into this. Here's my thought process on this:
**Analyzing `generic_file_mmap_prepare`**
Right, let's take a look at `generic_file_mmap_prepare`. I need to understand its role. It sounds like it's a preparation step for memory mapping a generic file. Given my expertise, I already have a pretty good idea of what that entails. My intuition tells me this function likely handles the initial setup and validation related to memory mapping a file, before the actual mapping takes place. It's probably responsible for things like checking permissions, validating the requested range, and potentially setting up any necessary internal data structures. Understanding this initial preparation phase is critical because it sets the stage for the performance and security of the `mmap` operation. I'm going to look for areas where errors are handled, because that will be very important.
|
| 37/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/fops.c IncludeLines:true Name:generic_file_mmap_prepare]
Results: map[SourceCode:4001: int generic_file_mmap_prepare(struct vm_area_desc *desc)
4002: {
4003: struct file *file = desc->file;
4004: struct address_space *mapping = file->f_mapping;
4005:
4006: if (!mapping->a_ops->read_folio)
4007: return -ENOEXEC;
4008: file_accessed(file);
4009: desc->vm_ops = &generic_file_vm_ops;
4010: return 0;
4011: }
SourceFile:mm/filemap.c]
|
| 38/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 21396
output: 41
thoughts: 137
Thoughts: **Analyzing the File Mapping Vulnerability**
Okay, let's break this down. My initial assumption was that `generic_file_mmap_prepare` somehow altered `desc->vm_file`. But that's not the case. It appears that `desc->vm_file` retains its original value, which was initialized to `vma->vm_file`. Consequently, `vma_set_file` isn't called, meaning `vma->vm_file` continues to point to `map->file`.
Now, according to the bug report, we're seeing "loop1: detected capacity change from 0 to 32768". This points to either `loop_set_status` or `loop_set_fd` being invoked. The capacity change is the key indicator here. Since we are in the analysis of a bug with memory maps and file systems, let's focus on `loop_set_fd` first, as file descriptors and mappings are inter-related. Let's see what's happening there.
|
| 39/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:drivers/block/loop.c IncludeLines:true Name:loop_set_fd]
Results: map[SourceCode: SourceFile:]
|
| 40/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 21818
output: 26
thoughts: 30
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the `loop` Block Device Driver**
Right, so I need to dig into the `loop` driver and figure out what's going on with these file descriptors or status updates. My first instinct, and the most logical starting point, is to go directly to the source code. I'm going to jump straight into the heart of the matter β the `drivers/block/loop.c` file. Given the functions I'm interested in, `loop_set_fd` or `loop_set_status` should be a good place to start my search. I expect to find the core logic for setting up the backing file and/or updating any status information related to the device. Let's see what we can find there.
|
| 41/2 |
2026/05/23 11:06 |
tool |
codesearch-file-index |
0m
Args: map[SourceFile:drivers/block/loop.c]
Results: map[Entities:[map[Kind:function Name:__check_max_part] map[Kind:function Name:__loop_clr_fd] map[Kind:function Name:do_req_filebacked] map[Kind:function Name:is_loop_device] map[Kind:function Name:lo_calculate_size] map[Kind:function Name:lo_can_use_dio] map[Kind:function Name:lo_compat_ioctl] map[Kind:function Name:lo_complete_rq] map[Kind:function Name:lo_fallocate] map[Kind:function Name:lo_free_disk] map[Kind:function Name:lo_ioctl] map[Kind:function Name:lo_open] map[Kind:function Name:lo_release] map[Kind:function Name:lo_req_flush] map[Kind:function Name:lo_rw_aio] map[Kind:function Name:lo_rw_aio_complete] map[Kind:function Name:lo_rw_aio_do_completion] map[Kind:function Name:lo_simple_ioctl] map[Kind:function Name:loop_add] map[Kind:function Name:loop_assign_backing_file] map[Kind:function Name:loop_attr_autoclear_show] map[Kind:function Name:loop_attr_backing_file_show] map[Kind:function Name:loop_attr_dio_show] map[Kind:function Name:loop_attr_do_show_autoclear] map[Kind:function Name:loop_attr_do_show_backing_file] map[Kind:function Name:loop_attr_do_show_dio] map[Kind:function Name:loop_attr_do_show_offset] map[Kind:function Name:loop_attr_do_show_partscan] map[Kind:function Name:loop_attr_do_show_sizelimit] map[Kind:function Name:loop_attr_offset_show] map[Kind:function Name:loop_attr_partscan_show] map[Kind:function Name:loop_attr_show] map[Kind:function Name:loop_attr_sizelimit_show] map[Kind:function Name:loop_change_fd] map[Kind:function Name:loop_check_backing_file] map[Kind:function Name:loop_clear_limits] map[Kind:function Name:loop_clr_fd] map[Kind:function Name:loop_configure] map[Kind:function Name:loop_control_get_free] map[Kind:function Name:loop_control_ioctl] map[Kind:function Name:loop_control_remove] map[Kind:function Name:loop_default_blocksize] map[Kind:function Name:loop_exit] map[Kind:function Name:loop_free_idle_workers] map[Kind:function Name:loop_free_idle_workers_timer] map[Kind:function Name:loop_get_discard_config] map[Kind:function Name:loop_get_status] map[Kind:function Name:loop_get_status64] map[Kind:function Name:loop_get_status_compat] map[Kind:function Name:loop_get_status_old] map[Kind:function Name:loop_global_lock_killable] map[Kind:function Name:loop_global_unlock] map[Kind:function Name:loop_handle_cmd] map[Kind:function Name:loop_info64_from_compat] map[Kind:function Name:loop_info64_from_old] map[Kind:function Name:loop_info64_to_compat] map[Kind:function Name:loop_info64_to_old] map[Kind:function Name:loop_init] map[Kind:function Name:loop_probe] map[Kind:function Name:loop_process_work] map[Kind:function Name:loop_query_min_dio_size] map[Kind:function Name:loop_queue_rq] map[Kind:function Name:loop_queue_work] map[Kind:function Name:loop_remove] map[Kind:function Name:loop_reread_partitions] map[Kind:function Name:loop_rootcg_workfn] map[Kind:function Name:loop_set_block_size] map[Kind:function Name:loop_set_capacity] map[Kind:function Name:loop_set_dio] map[Kind:function Name:loop_set_hw_queue_depth] map[Kind:function Name:loop_set_size] map[Kind:function Name:loop_set_status] map[Kind:function Name:loop_set_status64] map[Kind:function Name:loop_set_status_compat] map[Kind:function Name:loop_set_status_from_info] map[Kind:function Name:loop_set_status_old] map[Kind:function Name:loop_set_timer] map[Kind:function Name:loop_sysfs_exit] map[Kind:function Name:loop_sysfs_init] map[Kind:function Name:loop_update_dio] map[Kind:function Name:loop_update_limits] map[Kind:function Name:loop_validate_file] map[Kind:function Name:loop_workfn] map[Kind:function Name:max_loop_param_set_int] map[Kind:function Name:max_loop_setup] map[Kind:function Name:queue_on_root_worker] map[Kind:struct Name:compat_loop_info] map[Kind:struct Name:loop_cmd] map[Kind:struct Name:loop_device] map[Kind:struct Name:loop_worker] map[Kind:global_variable Name:__UNIQUE_ID_addressable_loop_init_1036] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1021] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1022] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1023] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1024] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1025] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1026] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1027] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1028] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1033] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1034] map[Kind:global_variable Name:__exitcall_loop_exit] map[Kind:global_variable Name:__param_hw_queue_depth] map[Kind:global_variable Name:__param_max_loop] map[Kind:global_variable Name:__param_max_part] map[Kind:global_variable Name:__param_str_hw_queue_depth] map[Kind:global_variable Name:__param_str_max_loop] map[Kind:global_variable Name:__param_str_max_part] map[Kind:global_variable Name:__setup_max_loop_setup] map[Kind:global_variable Name:__setup_str_max_loop_setup] map[Kind:global_variable Name:hw_queue_depth] map[Kind:global_variable Name:lo_fops] map[Kind:global_variable Name:loop_attr_autoclear] map[Kind:global_variable Name:loop_attr_backing_file] map[Kind:global_variable Name:loop_attr_dio] map[Kind:global_variable Name:loop_attr_offset] map[Kind:global_variable Name:loop_attr_partscan] map[Kind:global_variable Name:loop_attr_sizelimit] map[Kind:global_variable Name:loop_attribute_group] map[Kind:global_variable Name:loop_attrs] map[Kind:global_variable Name:loop_ctl_fops] map[Kind:global_variable Name:loop_ctl_mutex] map[Kind:global_variable Name:loop_hw_qdepth_param_ops] map[Kind:global_variable Name:loop_index_idr] map[Kind:global_variable Name:loop_misc] map[Kind:global_variable Name:loop_mq_ops] map[Kind:global_variable Name:loop_validate_mutex] map[Kind:global_variable Name:max_loop] map[Kind:global_variable Name:max_loop_param_ops]]]
|
| 42/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 24427
output: 39
thoughts: 406
Thoughts: **My Analysis of the `mmap` and Block Device Interaction**
Okay, I see `loop_change_fd` in the mix. My immediate thought is, "Can this function modify the backing file while it's actively mmapped?" That's a classic race condition scenario, something I need to carefully consider.
Ah, but a crucial point clicks: `mmap` isn't directly on the backing *file*, but on the block device (`/dev/loop1`). Of course! We're mapping the block device itself. This means the `file` pointer inside the `mmap_file` structure actually refers to the block device file, `/dev/loop1`.
Right, let's step through `blkdev_mmap_prepare`. The code grabs the `file` from the descriptor. Then it checks if the block device is read-only. If so it returns `generic_file_readonly_mmap_prepare`, otherwise `generic_file_mmap_prepare`. The critical part is `generic_file_mmap_prepare`. That calls `generic_file_vm_ops`. The crucial point is that this code doesn't change `desc->vm_file`. So, the `vma->vm_file` continues to reference the block device.
Okay, let's look at `vma_link_file`. Here, `file` gets assigned from `vma->vm_file`. Then, we have `mapping = file->f_mapping;` followed by `i_mmap_lock_write(mapping);`. If, as I suspect, `file` is indeed the block device file, then `file->f_mapping` points to the block device's mapping. That makes sense. I have to wonder: Why would `file->f_mapping` ever be associated with a user-space address? The structure implies it's a kernel-level mapping.
A key question arises: Is there any mechanism, outside the specific path I've followed, that could potentially modify `vma->vm_file`? I need to review `mmap_region` again to ensure I haven't missed a crucial detail. I need to be absolutely certain of the flow and the implications of this mmap's interaction with the block device.
|
| 43/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:mmap_region]
Results: map[SourceCode:2795: /**
2796: * mmap_region() - Actually perform the userland mapping of a VMA into
2797: * current->mm with known, aligned and overflow-checked @addr and @len, and
2798: * correctly determined VMA flags @vm_flags and page offset @pgoff.
2799: *
2800: * This is an internal memory management function, and should not be used
2801: * directly.
2802: *
2803: * The caller must write-lock current->mm->mmap_lock.
2804: *
2805: * @file: If a file-backed mapping, a pointer to the struct file describing the
2806: * file to be mapped, otherwise NULL.
2807: * @addr: The page-aligned address at which to perform the mapping.
2808: * @len: The page-aligned, non-zero, length of the mapping.
2809: * @vm_flags: The VMA flags which should be applied to the mapping.
2810: * @pgoff: If @file is specified, the page offset into the file, if not then
2811: * the virtual page offset in memory of the anonymous mapping.
2812: * @uf: Optionally, a pointer to a list head used for tracking userfaultfd unmap
2813: * events.
2814: *
2815: * Returns: Either an error, or the address at which the requested mapping has
2816: * been performed.
2817: */
2818: unsigned long mmap_region(struct file *file, unsigned long addr,
2819: unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
2820: struct list_head *uf)
2821: {
2822: unsigned long ret;
2823: bool writable_file_mapping = false;
2824:
2825: mmap_assert_write_locked(current->mm);
2826:
2827: /* Check to see if MDWE is applicable. */
2828: if (map_deny_write_exec(vm_flags, vm_flags))
2829: return -EACCES;
2830:
2831: /* Allow architectures to sanity-check the vm_flags. */
2832: if (!arch_validate_flags(vm_flags))
2833: return -EINVAL;
2834:
2835: /* Map writable and ensure this isn't a sealed memfd. */
2836: if (file && is_shared_maywrite_vm_flags(vm_flags)) {
2837: int error = mapping_map_writable(file->f_mapping);
2838:
2839: if (error)
2840: return error;
2841: writable_file_mapping = true;
2842: }
2843:
2844: ret = __mmap_region(file, addr, len, vm_flags, pgoff, uf);
2845:
2846: /* Clear our write mapping regardless of error. */
2847: if (writable_file_mapping)
2848: mapping_unmap_writable(file->f_mapping);
2849:
2850: validate_mm(current->mm);
2851: return ret;
2852: }
SourceFile:mm/vma.c]
|
| 44/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 26314
output: 40
thoughts: 12
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the Call to `__mmap_region`**
Okay, so I'm seeing a call to `__mmap_region`. My immediate thought is, "Ah, we're dealing with memory mapping." This function is the key to managing virtual memory regions, the bread and butter for any decent memory management scheme. I need to understand *why* this call is happening now. What's the context? What's the underlying operation driving this? Is it a request for a new allocation? Resizing an existing mapping? Protection change? De-allocation?
I need to dive deeper into the surrounding code to determine which scenario we're currently in. The arguments being passed to `__mmap_region` are crucial. What's the file descriptor (if any), offset, size, flags, and permissions? Those will tell the full story. I'll be looking for potential problems: Do the flags align with the expected behavior? Are we using the correct access permissions for the target memory area? Are there any obvious alignment issues or size restrictions that could introduce errors? Is the offset sensible?
I also need to check how the return value from `__mmap_region` is handled. If it's successful, we'll get a virtual address back. If it fails, there'll be an error code. How does the calling function react to a failure? Are we handling the error correctly? Are we potentially leaking resources if the mapping fails partway through some critical initialization process? And are we considering all possible error scenarios?
Furthermore, I have to ensure that we're properly tracking the mapping. Are we maintaining a consistent view of the virtual address space? Are we updating any relevant data structures, such as page tables or memory maps? Any inconsistencies here would lead to serious problems like segmentation faults or data corruption. Finally, as an optimization check, I also want to make sure this is the most efficient mapping strategy for the situation. Could we optimize by using huge pages, for example, or is this the appropriate mapping size? I'll probably start scanning the code in its vicinity.
|
| 45/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:__mmap_region]
Results: map[SourceCode:2720: static unsigned long __mmap_region(struct file *file, unsigned long addr,
2721: unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
2722: struct list_head *uf)
2723: {
2724: struct mm_struct *mm = current->mm;
2725: struct vm_area_struct *vma = NULL;
2726: bool have_mmap_prepare = file && file->f_op->mmap_prepare;
2727: VMA_ITERATOR(vmi, mm, addr);
2728: MMAP_STATE(map, mm, &vmi, addr, len, pgoff, vm_flags, file);
2729: struct vm_area_desc desc = {
2730: .mm = mm,
2731: .file = file,
2732: .action = {
2733: .type = MMAP_NOTHING, /* Default to no further action. */
2734: },
2735: };
2736: bool allocated_new = false;
2737: int error;
2738:
2739: map.check_ksm_early = can_set_ksm_flags_early(&map);
2740:
2741: error = __mmap_setup(&map, &desc, uf);
2742: if (!error && have_mmap_prepare)
2743: error = call_mmap_prepare(&map, &desc);
2744: if (error)
2745: goto abort_munmap;
2746:
2747: if (map.check_ksm_early)
2748: update_ksm_flags(&map);
2749:
2750: /* Attempt to merge with adjacent VMAs... */
2751: if (map.prev || map.next) {
2752: VMG_MMAP_STATE(vmg, &map, /* vma = */ NULL);
2753:
2754: vma = vma_merge_new_range(&vmg);
2755: }
2756:
2757: /* ...but if we can't, allocate a new VMA. */
2758: if (!vma) {
2759: error = __mmap_new_vma(&map, &vma);
2760: if (error)
2761: goto unacct_error;
2762: allocated_new = true;
2763: }
2764:
2765: if (have_mmap_prepare)
2766: set_vma_user_defined_fields(vma, &map);
2767:
2768: __mmap_complete(&map, vma);
2769:
2770: if (have_mmap_prepare && allocated_new) {
2771: error = call_action_complete(&map, &desc, vma);
2772:
2773: if (error)
2774: return error;
2775: }
2776:
2777: return addr;
2778:
2779: /* Accounting was done by __mmap_setup(). */
2780: unacct_error:
2781: if (map.charged)
2782: vm_unacct_memory(map.charged);
2783: abort_munmap:
2784: /*
2785: * This indicates that .mmap_prepare has set a new file, differing from
2786: * desc->vm_file. But since we're aborting the operation, only the
2787: * original file will be cleaned up. Ensure we clean up both.
2788: */
2789: if (map.file_doesnt_need_get)
2790: fput(map.file);
2791: vms_abort_munmap_vmas(&map.vms, &map.mas_detach);
2792: return error;
2793: }
SourceFile:mm/vma.c]
|
| 46/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 27973
output: 41
thoughts: 38
Thoughts: Okay, let's see. Here's my understanding, as if these were my thoughts:
**Analyzing `call_mmap_prepare` and `__mmap_new_vma`**
Right, so I'm noticing a critical sequence here. Specifically, `call_mmap_prepare` is being called *prior* to `__mmap_new_vma`. That's a key observation. It tells me something about the memory mapping process. Now I need to understand why this ordering is significant. Let me focus on `call_mmap_prepare` itself. I need to refresh my understanding of its role in this entire flow and what it sets up before the VMA is even created. I should look into the specific arguments passed, any potential side effects or initializations it performs, and how those factors relate to the state expected by `__mmap_new_vma`. This initial preparation stage must be key.
|
| 47/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:call_mmap_prepare]
Results: map[SourceCode:2627: /*
2628: * Invoke the f_op->mmap_prepare() callback for a file-backed mapping that
2629: * specifies it.
2630: *
2631: * This is called prior to any merge attempt, and updates whitelisted fields
2632: * that are permitted to be updated by the caller.
2633: *
2634: * All but user-defined fields will be pre-populated with original values.
2635: *
2636: * Returns 0 on success, or an error code otherwise.
2637: */
2638: static int call_mmap_prepare(struct mmap_state *map,
2639: struct vm_area_desc *desc)
2640: {
2641: int err;
2642:
2643: /* Invoke the hook. */
2644: err = vfs_mmap_prepare(map->file, desc);
2645: if (err)
2646: return err;
2647:
2648: call_action_prepare(map, desc);
2649:
2650: /* Update fields permitted to be changed. */
2651: map->pgoff = desc->pgoff;
2652: if (desc->vm_file != map->file) {
2653: map->file_doesnt_need_get = true;
2654: map->file = desc->vm_file;
2655: }
2656: map->vma_flags = desc->vma_flags;
2657: map->page_prot = desc->page_prot;
2658: /* User-defined fields. */
2659: map->vm_ops = desc->vm_ops;
2660: map->vm_private_data = desc->private_data;
2661:
2662: return 0;
2663: }
SourceFile:mm/vma.c]
|
| 48/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 28814
output: 23
thoughts: 220
Thoughts: **My Analysis of the Kernel Memory Mapping Process**
Okay, so I'm tracing this `mmap` path, and I'm seeing that `vfs_mmap_prepare` is the key function, as expected. It calls the `file->f_op->mmap_prepare` hook, which makes sense. I see that for block devices, `blkdev_mmap_prepare` is called, which then calls `generic_file_mmap_prepare`. Now, the critical point is that `generic_file_mmap_prepare` doesn't actually *modify* `desc->vm_file`. This is important.
So, `desc->vm_file` remains what was set previously, which is `map->file`. That seems correct. Now, hold on a second... where is `desc->vm_file` initialized in the first place? I don't see it being set during the initial `__mmap_region` call. Let's dig into that code block:
```c
struct vm_area_desc desc = {
.mm = mm,
.file = file,
.action = {
.type = MMAP_NOTHING, /* Default to no further action. */
},
};
```
Aha! `desc.vm_file` is NOT initialized. That means it will be `NULL`. This is a bug waiting to happen, or at least unexpected behavior. I'm going to have to check the definition of `struct vm_area_desc` to understand how this isn't causing obvious problems. The fact that it doesn't cause obvious problems now is itself a red flag.
|
| 49/2 |
2026/05/23 11:06 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:mm OffsetBits:0 SizeBits:64] map[Name:file OffsetBits:64 SizeBits:64] map[Name:start OffsetBits:128 SizeBits:64] map[Name:end OffsetBits:192 SizeBits:64] map[Name:pgoff OffsetBits:256 SizeBits:64] map[Name:vm_file OffsetBits:320 SizeBits:64] map[Name:vma_flags OffsetBits:384 SizeBits:64] map[Name:page_prot OffsetBits:448 SizeBits:64] map[Name:vm_ops OffsetBits:512 SizeBits:64] map[Name:private_data OffsetBits:576 SizeBits:64] map[Name:action OffsetBits:640 SizeBits:512]]]
|
| 50/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 29652
output: 40
thoughts: 139
Thoughts: **Analyzing the Memory Mapping Process**
Okay, so I'm looking at this memory mapping code and confirming that `desc.vm_file` is indeed located at offset 320 bits, which is what I expected. Now, in the `__mmap_region` function, there's this `vm_area_desc` structure being declared and initialized. The key here is the initialization:
```c
struct vm_area_desc desc = {
.mm = mm,
.file = file,
.action = {
.type = MMAP_NOTHING, /* Default to no further action. */
},
};
```
Since the compiler zero-initializes any fields in `desc` that aren't explicitly assigned, I understand that `desc.vm_file` will be `NULL` initially. But wait, this doesn't fully account for `__mmap_setup`. That function might be where it gets initialized. I'll need to double check how the setup function handles this to be certain of its ultimate value.
|
| 51/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:__mmap_setup]
Results: map[SourceCode:2379: /*
2380: * __mmap_setup() - Prepare to gather any overlapping VMAs that need to be
2381: * unmapped once the map operation is completed, check limits, account mapping
2382: * and clean up any pre-existing VMAs.
2383: *
2384: * As a result it sets up the @map and @desc objects.
2385: *
2386: * @map: Mapping state.
2387: * @desc: VMA descriptor
2388: * @uf: Userfaultfd context list.
2389: *
2390: * Returns: 0 on success, error code otherwise.
2391: */
2392: static int __mmap_setup(struct mmap_state *map, struct vm_area_desc *desc,
2393: struct list_head *uf)
2394: {
2395: int error;
2396: struct vma_iterator *vmi = map->vmi;
2397: struct vma_munmap_struct *vms = &map->vms;
2398:
2399: /* Find the first overlapping VMA and initialise unmap state. */
2400: vms->vma = vma_find(vmi, map->end);
2401: init_vma_munmap(vms, vmi, vms->vma, map->addr, map->end, uf,
2402: /* unlock = */ false);
2403:
2404: /* OK, we have overlapping VMAs - prepare to unmap them. */
2405: if (vms->vma) {
2406: mt_init_flags(&map->mt_detach,
2407: vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
2408: mt_on_stack(map->mt_detach);
2409: mas_init(&map->mas_detach, &map->mt_detach, /* addr = */ 0);
2410: /* Prepare to unmap any existing mapping in the area */
2411: error = vms_gather_munmap_vmas(vms, &map->mas_detach);
2412: if (error) {
2413: /* On error VMAs will already have been reattached. */
2414: vms->nr_pages = 0;
2415: return error;
2416: }
2417:
2418: map->next = vms->next;
2419: map->prev = vms->prev;
2420: } else {
2421: map->next = vma_iter_next_rewind(vmi, &map->prev);
2422: }
2423:
2424: /* Check against address space limit. */
2425: if (!may_expand_vm(map->mm, map->vm_flags, map->pglen - vms->nr_pages))
2426: return -ENOMEM;
2427:
2428: /* Private writable mapping: check memory availability. */
2429: if (accountable_mapping(map->file, map->vm_flags)) {
2430: map->charged = map->pglen;
2431: map->charged -= vms->nr_accounted;
2432: if (map->charged) {
2433: error = security_vm_enough_memory_mm(map->mm, map->charged);
2434: if (error)
2435: return error;
2436: }
2437:
2438: vms->nr_accounted = 0;
2439: map->vm_flags |= VM_ACCOUNT;
2440: }
2441:
2442: /*
2443: * Clear PTEs while the vma is still in the tree so that rmap
2444: * cannot race with the freeing later in the truncate scenario.
2445: * This is also needed for mmap_file(), which is why vm_ops
2446: * close function is called.
2447: */
2448: vms_clean_up_area(vms, &map->mas_detach);
2449:
2450: set_desc_from_map(desc, map);
2451: return 0;
2452: }
SourceFile:mm/vma.c]
|
| 52/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 31291
output: 42
thoughts: 32
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the code:
**Diving into the Description Setter**
Right, so `set_desc_from_map(desc, map)` is being called. My first instinct is to immediately jump in and analyze that function. I need to understand what it's doing with `desc` and `map`. What's the purpose of this call? What is the function trying to achieve? Is it constructing the description? Modifying it? The parameters give me clues, but I need the full context to know for sure. I'm going to quickly check the definition of `set_desc_from_map` and look at its implementation. I'm hoping I can refresh my understanding of how this particular process works. I'll focus on the data flow and any logic that manipulates the input arguments.
|
| 53/2 |
2026/05/23 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:set_desc_from_map]
Results: map[SourceCode:2367: static void set_desc_from_map(struct vm_area_desc *desc,
2368: const struct mmap_state *map)
2369: {
2370: desc->start = map->addr;
2371: desc->end = map->end;
2372:
2373: desc->pgoff = map->pgoff;
2374: desc->vm_file = map->file;
2375: desc->vma_flags = map->vma_flags;
2376: desc->page_prot = map->page_prot;
2377: }
SourceFile:mm/vma.c]
|
| 54/2 |
2026/05/23 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 31750
output: 41
thoughts: 1123
Thoughts: **Double-Checking the `mmap` Flow**
Okay, so I'm tracing the `mmap` process here, and something's bugging me. Initially, `desc->vm_file` gets set to `map->file`. Then, `call_mmap_prepare` is invoked, which calls `vfs_mmap_prepare` (like `blkdev_mmap_prepare`). After that `map->file` can be modified to be `desc->vm_file`. If `vfs_mmap_prepare` *doesn't* change the `desc->vm_file`, then `map->file` remains unchanged, which is normal.
Then, `__mmap_new_vma` is called, and, if a file is present, `__mmap_new_file_vma` gets called. Now, inside `__mmap_new_file_vma`, `vma->vm_file` gets assigned, which is `map->file`. The code then checks if the file has an `mmap` function in the file operations structure. If it exists, then `mmap_file` is called, which calls `vfs_mmap`.
And here's where it gets interesting: `vfs_mmap` *might* call `compat_vma_mmap` if `f_op->mmap_prepare` exists. If it does, `compat_vma_mmap` calls `__compat_vma_mmap`, which *also* calls `f_op->mmap_prepare`!
Wait, *what*? The `mmap_prepare` function is being called *twice* in the flow! Once in `__mmap_region` through `call_mmap_prepare`, and then again through the `compat_vma_mmap` path. That seems redundant, and I need to figure out why.
Looking back, the code in `__mmap_region` explicitly checks for `file->f_op->mmap_prepare` before calling `call_mmap_prepare`. If it's present, `call_mmap_prepare` does its thing. Then, regardless of the mmap prepare call, `__mmap_new_vma` is called. Inside of that, if there is an associated file with the map, `__mmap_new_file_vma` is called. It checks the f_op for the mmap operation, and if that's there, it calls `mmap_file`, which in turn calls `vfs_mmap`.
Okay, so for *block* devices, the `def_blk_fops` structure *doesn't* have an `.mmap` operation. Why does it not have an mmap operation? I'll need to go back and verify `def_blk_fops` again.
|
| 55/2 |
2026/05/23 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/fops.c IncludeLines:true Name:def_blk_fops]
Results: map[SourceCode: 952: const struct file_operations def_blk_fops = {
953: .open = blkdev_open,
954: .release = blkdev_release,
955: .llseek = blkdev_llseek,
956: .read_iter = blkdev_read_iter,
957: .write_iter = blkdev_write_iter,
958: .iopoll = iocb_bio_iopoll,
959: .mmap_prepare = blkdev_mmap_prepare,
960: .fsync = blkdev_fsync,
961: .unlocked_ioctl = blkdev_ioctl,
962: #ifdef CONFIG_COMPAT
963: .compat_ioctl = compat_blkdev_ioctl,
964: #endif
965: .splice_read = filemap_splice_read,
966: .splice_write = iter_file_splice_write,
967: .fallocate = blkdev_fallocate,
968: .uring_cmd = blkdev_uring_cmd,
969: .fop_flags = FOP_BUFFER_RASYNC,
970: };
SourceFile:block/fops.c]
|
| 56/2 |
2026/05/23 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 33917
output: 45
thoughts: 1200
Thoughts: **Analyzing the Block Device mmap Flow**
Okay, let's break this down. First, I see that the code checks for the existence of `.mmap`: `!map->file->f_op->mmap`. If this is true, the function immediately returns 0. That's a critical point.
If `.mmap` is *not* present, `__mmap_new_file_vma` returns 0 right away. This means `mmap_file` and, subsequently, `compat_vma_mmap`, are *never* called. The `vma->vm_file` would then remain the original `map->file`, which, in this scenario, is the block device file.
Then, the code continues to `vma_link_file`. Inside `vma_link_file`, `file->f_mapping` becomes the block device's mapping. My initial thought was: how can this mapping possibly contain a user-space address?
I have to consider if `map->file` could be modified by `call_mmap_prepare`. Let me re-examine `blkdev_mmap_prepare`. It calls `generic_file_mmap_prepare` if the block device is not read-only. Inspecting `generic_file_mmap_prepare`, it *doesn't* alter `desc->vm_file`, meaning the original `map->file` remains unchanged. So `call_mmap_prepare` does NOT change `map->file`!
But what if the file being mmapped *isn't* the block device itself? The bug report mentions a "loop1" device, which indicates a *loop* device is involved. Could the file be *on* the loop device? If it's a regular file on the loop device, it would normally have a `f_op->mmap` function like `generic_file_mmap`.
Now I need to consider what happens if `f_op->mmap_prepare` *is* set, but `.mmap` is *not*. If `f_op->mmap_prepare` is set but not `.mmap`, then `call_mmap_prepare` is never called. So, `__mmap_new_file_vma` then *does* call `mmap_file`. `mmap_file` calls `vfs_mmap`, and `vfs_mmap` calls the file's `f_op->mmap`. Does the file's `f_op->mmap` change `vma->vm_file`? Yes, some drivers might. Overlayfs and ecryptfs, for example.
But the key clue is still "loop1: detected capacity change". This suggests the loop device itself is being mmapped.
The code's critical check is:
```c
if (!map->file->f_op->mmap)
return 0;
```
If `.mmap` is *missing* but `.mmap_prepare` *is* present in `def_blk_fops`, then `vfs_mmap` would NEVER be called for it in `__mmap_new_file_vma`!
And yes, I now recall the recent mmap API changes: It *is* valid to have `.mmap_prepare` without `.mmap`.
So, if a file has `.mmap_prepare` but *no* `.mmap`, `__mmap_new_file_vma` will see `!map->file->f_op->mmap` and return 0. This is the heart of the problem!
|
| 57/2 |
2026/05/23 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:__mmap_new_file_vma]
Results: map[SourceCode:2455: static int __mmap_new_file_vma(struct mmap_state *map,
2456: struct vm_area_struct *vma)
2457: {
2458: struct vma_iterator *vmi = map->vmi;
2459: int error;
2460:
2461: vma->vm_file = map->file;
2462: if (!map->file_doesnt_need_get)
2463: get_file(map->file);
2464:
2465: if (!map->file->f_op->mmap)
2466: return 0;
2467:
2468: error = mmap_file(vma->vm_file, vma);
2469: if (error) {
2470: UNMAP_STATE(unmap, vmi, vma, vma->vm_start, vma->vm_end,
2471: map->prev, map->next);
2472: fput(vma->vm_file);
2473: vma->vm_file = NULL;
2474:
2475: vma_iter_set(vmi, vma->vm_end);
2476: /* Undo any partial mapping done by a device driver. */
2477: unmap_region(&unmap);
2478: return error;
2479: }
2480:
2481: /* Drivers cannot alter the address of the VMA. */
2482: WARN_ON_ONCE(map->addr != vma->vm_start);
2483: /*
2484: * Drivers should not permit writability when previously it was
2485: * disallowed.
2486: */
2487: VM_WARN_ON_ONCE(map->vm_flags != vma->vm_flags &&
2488: !(map->vm_flags & VM_MAYWRITE) &&
2489: (vma->vm_flags & VM_MAYWRITE));
2490:
2491: map->file = vma->vm_file;
2492: map->vm_flags = vma->vm_flags;
2493:
2494: return 0;
2495: }
SourceFile:mm/vma.c]
|
| 58/2 |
2026/05/23 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 36609
output: 42
thoughts: 1013
Thoughts: **Debugging a Potential mmap Vulnerability**
Okay, here's the situation. I'm looking at this code and something doesn't seem right in how it handles memory mapping, specifically in the context of the new `.mmap_prepare` API.
First off, I'm noting that if `!map->file->f_op->mmap` is true, a zero is returned. That means the code skips `mmap_file`. Now, if a file utilizes the `.mmap_prepare` hook and *doesn't* define `.mmap`, `__mmap_new_file_vma` skips calling `mmap_file`. This immediately raises a red flag. Isn't `mmap_file` the *only* place where `vfs_mmap` gets called?
If `mmap_file` is skipped, does that mean the driver's mmap hook isn't called during VMA creation? But, wait... I see `call_mmap_prepare` was *already* called in `__mmap_region`! This means the driver *was* able to register the hook. Then, looking at `__mmap_new_file_vma`:
```c
if (!map->file->f_op->mmap)
return 0;
```
If a driver *only* implements `.mmap_prepare`, returning 0 makes it all the way to `vma_link_file`! Which is fine.
```c
vma_link_file(vma, map->hold_file_rmap_lock);
```
Okay, so `vma->vm_file` is set to `map->file` as expected:
```c
vma->vm_file = map->file;
```
And then:
```c
if (file) {
mapping = file->f_mapping;
i_mmap_lock_write(mapping);
```
Okay, `mapping` is therefore `map->file->f_mapping`. But here's the rub - why would `map->file->f_mapping` be a user-space address? This seems like a potential security vulnerability.
I have to wonder, could `map->file` be something *other* than the block device file after `call_mmap_prepare` runs? Let me check again.
```c
err = vfs_mmap_prepare(map->file, desc);
if (err)
return err;
call_action_prepare(map, desc);
/* Update fields permitted to be changed. */
map->pgoff = desc->pgoff;
if (desc->vm_file != map->file) {
map->file_doesnt_need_get = true;
map->file = desc->vm_file;
}
```
Wait! `desc->vm_file` was initialized to `map->file`, so it should be valid initially! Now, does `blkdev_mmap_prepare` or `generic_file_mmap_prepare` alter `desc->vm_file`? No, they don't. So, `map->file` *should* remain the block device file.
So, *why* is `file->f_mapping` a user-space address? Could `file` *itself* be a user-space address? That would mean reading `file->f_mapping` from user-space memory!
How could `map->file` become a user-space address? Ah, look at this:
```c
if (desc->vm_file != map->file) {
map->file_doesnt_need_get = true;
map->file = desc->vm_file;
}
```
If `desc->vm_file` is modified to a user-space address, then `map->file` *becomes* a user-space address! Who could possibly change `desc->vm_file`?
`desc` gets passed to `vfs_mmap_prepare` - which is the final piece.
```c
err = vfs_mmap_prepare(map->file, desc);
```
I need to dig into `vfs_mmap_prepare` to see how it might change `desc->vm_file`. This is the critical next step.
|
| 59/2 |
2026/05/23 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:vfs_mmap_prepare]
Results: map[SourceCode:2073: static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
2074: {
2075: return file->f_op->mmap_prepare(desc);
2076: }
SourceFile:include/linux/fs.h]
|
| 60/2 |
2026/05/23 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 38726
output: 39
thoughts: 877
Thoughts: **Analyzing the Block Device mmap Flow**
Okay, let's break this down. My initial observation is that `desc` is a local `struct vm_area_desc` on the stack, allocated within `__mmap_region`. This `desc` is then passed to `__mmap_setup`. The crucial part is how `desc` is populated and used. `__mmap_setup` calls `set_desc_from_map`, which initializes many fields of `desc`, including `desc->vm_file` with `map->file`. Now, `map->file` at this point is the block device file as passed to `mmap`.
The key function here is `call_mmap_prepare`, which subsequently calls `vfs_mmap_prepare`. If we're dealing with a block device, this leads to a call to `generic_file_mmap_prepare`. Inside `generic_file_mmap_prepare`, the code uses `desc->file` (initialized in `__mmap_region`) to retrieve the `f_mapping`, NOT `desc->vm_file`. This is important because `desc->file` remains unchanged after initialization. The crucial check is: `if (desc->vm_file != map->file)`. Here, `desc->vm_file` and `map->file` will always be the same, so no `map->file` changes. It means `map->file` is never replaced with some other value.
Therefore, `map->file` remains the block device file. Subsequently, `__mmap_new_file_vma` correctly sets `vma->vm_file` to this block device file. And finally, in `vma_link_file`, the code retrieves the block device file and the `f_mapping`. So the question becomes: how is the backing file relevant here?
The bug report mentions the "loop1: detected capacity change". This suggests a `loop_set_fd` or `loop_configure` call must have happened at some point. It's time to check what occurs inside `loop_configure`, to see how this fits into the mmap flow and how a backing file could be involved here.
|
| 61/2 |
2026/05/23 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/loop.c IncludeLines:true Name:loop_configure]
Results: map[SourceCode: 981: static int loop_configure(struct loop_device *lo, blk_mode_t mode,
982: struct block_device *bdev,
983: const struct loop_config *config)
984: {
985: struct file *file = fget(config->fd);
986: struct queue_limits lim;
987: int error;
988: loff_t size;
989: bool partscan;
990: bool is_loop;
991:
992: if (!file)
993: return -EBADF;
994:
995: error = loop_check_backing_file(file);
996: if (error) {
997: fput(file);
998: return error;
999: }
1000:
1001: is_loop = is_loop_device(file);
1002:
1003: /* This is safe, since we have a reference from open(). */
1004: __module_get(THIS_MODULE);
1005:
1006: /*
1007: * If we don't hold exclusive handle for the device, upgrade to it
1008: * here to avoid changing device under exclusive owner.
1009: */
1010: if (!(mode & BLK_OPEN_EXCL)) {
1011: error = bd_prepare_to_claim(bdev, loop_configure, NULL);
1012: if (error)
1013: goto out_putf;
1014: }
1015:
1016: error = loop_global_lock_killable(lo, is_loop);
1017: if (error)
1018: goto out_bdev;
1019:
1020: error = -EBUSY;
1021: if (lo->lo_state != Lo_unbound)
1022: goto out_unlock;
1023:
1024: error = loop_validate_file(file, bdev);
1025: if (error)
1026: goto out_unlock;
1027:
1028: if ((config->info.lo_flags & ~LOOP_CONFIGURE_SETTABLE_FLAGS) != 0) {
1029: error = -EINVAL;
1030: goto out_unlock;
1031: }
1032:
1033: error = loop_set_status_from_info(lo, &config->info);
1034: if (error)
1035: goto out_unlock;
1036: lo->lo_flags = config->info.lo_flags;
1037:
1038: if (!(file->f_mode & FMODE_WRITE) || !(mode & BLK_OPEN_WRITE) ||
1039: !file->f_op->write_iter)
1040: lo->lo_flags |= LO_FLAGS_READ_ONLY;
1041:
1042: if (!lo->workqueue) {
1043: lo->workqueue = alloc_workqueue("loop%d",
1044: WQ_UNBOUND | WQ_FREEZABLE,
1045: 0, lo->lo_number);
1046: if (!lo->workqueue) {
1047: error = -ENOMEM;
1048: goto out_unlock;
1049: }
1050: }
1051:
1052: /* suppress uevents while reconfiguring the device */
1053: dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
1054:
1055: disk_force_media_change(lo->lo_disk);
1056: set_disk_ro(lo->lo_disk, (lo->lo_flags & LO_FLAGS_READ_ONLY) != 0);
1057:
1058: lo->lo_device = bdev;
1059: loop_assign_backing_file(lo, file);
1060:
1061: lim = queue_limits_start_update(lo->lo_queue);
1062: loop_update_limits(lo, &lim, config->block_size);
1063: /* No need to freeze the queue as the device isn't bound yet. */
1064: error = queue_limits_commit_update(lo->lo_queue, &lim);
1065: if (error)
1066: goto out_unlock;
1067:
1068: /*
1069: * We might switch to direct I/O mode for the loop device, write back
1070: * all dirty data the page cache now that so that the individual I/O
1071: * operations don't have to do that.
1072: */
1073: vfs_fsync(file, 0);
1074:
1075: loop_update_dio(lo);
1076: loop_sysfs_init(lo);
1077:
1078: size = lo_calculate_size(lo, file);
1079: loop_set_size(lo, size);
1080:
1081: /* Order wrt reading lo_state in loop_validate_file(). */
1082: wmb();
1083:
1084: WRITE_ONCE(lo->lo_state, Lo_bound);
1085: if (part_shift)
1086: lo->lo_flags |= LO_FLAGS_PARTSCAN;
1087: partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
1088: if (partscan)
1089: clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
1090:
1091: dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
1092: kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
1093:
1094: loop_global_unlock(lo, is_loop);
1095: if (partscan)
1096: loop_reread_partitions(lo);
1097:
1098: if (!(mode & BLK_OPEN_EXCL))
1099: bd_abort_claiming(bdev, loop_configure);
1100:
1101: return 0;
1102:
1103: out_unlock:
1104: loop_global_unlock(lo, is_loop);
1105: out_bdev:
1106: if (!(mode & BLK_OPEN_EXCL))
1107: bd_abort_claiming(bdev, loop_configure);
1108: out_putf:
1109: fput(file);
1110: /* This is safe: open() is still holding a reference. */
1111: module_put(THIS_MODULE);
1112: return error;
1113: }
SourceFile:drivers/block/loop.c]
|
| 62/2 |
2026/05/23 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 42122
output: 41
thoughts: 428
Thoughts: **My Analysis of the `mmap` Process for Block Devices**
Okay, so I'm trying to trace how `mmap` works with loop devices, specifically in relation to how `loop_configure` sets up the backing file. My train of thought starts with: how does this backing file relate to the memory mapping of the loop device? If I'm `mmap`ing `/dev/loop1`, I'm actually mapping the underlying block device, right?
Right! So the `mmap_prepare` function for block devices is `blkdev_mmap_prepare`. Let's see what that does.
Ah, `blkdev_mmap_prepare` checks something interesting:
```c
static int blkdev_mmap_prepare(struct vm_area_desc *desc)
{
struct file *file = desc->file;
if (bdev_read_only(I_BDEV(bdev_file_inode(file))))
return generic_file_readonly_mmap_prepare(desc);
return generic_file_mmap_prepare(desc);
}
```
Wait, `bdev_file_inode(file)` gets the inode of the *block device* file, and `I_BDEV` extracts the `struct block_device`. Then `bdev_read_only` determines if it is read-only. If it is read only, then `generic_file_readonly_mmap_prepare` gets called. Otherwise, it moves on to `generic_file_mmap_prepare`.
Let's look at `generic_file_mmap_prepare`:
```c
int generic_file_mmap_prepare(struct vm_area_desc *desc)
{
struct file *file = desc->file;
struct address_space *mapping = file->f_mapping;
if (!mapping->a_ops->read_folio)
return -ENOEXEC;
file_accessed(file);
desc->vm_ops = &generic_file_vm_ops;
return 0;
}
```
Okay, the crucial part here is the check on `mapping->a_ops->read_folio`. The return code `-ENOEXEC` says "Executable format error", and since this is preparing for a mapping, it implies it needs that functionality. For a block device, `file->f_mapping` *should* be the block device's mapping, which is the `bd_inode->i_mapping`. Does a block device's mapping actually have the `read_folio` operation? I need to look at `def_blk_aops` to confirm. I bet that's the answer.
|
| 63/2 |
2026/05/23 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/fops.c IncludeLines:true Name:def_blk_aops]
Results: map[SourceCode: 524: const struct address_space_operations def_blk_aops = {
525: .dirty_folio = block_dirty_folio,
526: .invalidate_folio = block_invalidate_folio,
527: .read_folio = blkdev_read_folio,
528: .readahead = blkdev_readahead,
529: .writepages = blkdev_writepages,
530: .write_begin = blkdev_write_begin,
531: .write_end = blkdev_write_end,
532: .migrate_folio = buffer_migrate_folio_norefs,
533: .is_dirty_writeback = buffer_check_dirty_writeback,
534: };
SourceFile:block/fops.c]
|
| 64/2 |
2026/05/23 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 43425
output: 21
thoughts: 810
Thoughts: **Analyzing a Kernel Memory Mapping Bug**
Okay, let's break this down. We've got a crash related to `i_mmap_lock_write`, and it seems to involve a block device, specifically `loop1` as indicated by the kernel log. The debugger's flow has shown that `read_folio` is involved, and `generic_file_mmap_prepare` returns 0, so that means we're in the mmap path. Then `__mmap_new_file_vma` is called. It looks like it doesn't have an `.mmap` operation because `def_blk_fops` is in play. So, `__mmap_new_file_vma` returns 0.
Now, `vma_link_file` is called. Inside this, the code accesses `file->f_mapping` for locking. The crucial point is that `file` here *should* be the block device file, since `vma->vm_file` in `__mmap_new_file_vma` is set from `map->file`, and `map->file` should be the block device file as passed into the `mmap` call.
However, the question is how `file->f_mapping` could be a user-space address, which is the root cause of the crash. It seems very weird. It's not supposed to be! The `mapping` should be a kernel address. I start wondering if `file` is *not* what it is expected to be. I consider if `map->file` has been modified somewhere.
Wait, `mmap_region` can take a file that's not a block device. The "loop1" message might be a red herring, or it could be related to syzkaller fuzzing. Maybe it was messing with loop devices *before* calling `mmap` on something else.
Okay, back to the problem. If we have a crash in `i_mmap_lock_write(mapping)`, where `mapping` is a user-space address, then `file->f_mapping` must be a user-space address, which is impossible, unless the `struct file` itself has been corrupted. Can `f_mapping` be overwritten somehow? Or could the `file` pointer *itself* be a user-space address? If `file` is user-space, then `vma->vm_file` in the vma would be user-space too. And tracing back, in `__mmap_new_file_vma` we're setting `vma->vm_file = map->file`, so `map->file` is the culprit.
This means `map->file` *must* be user-space. So, how could `map->file` be set to a user-space address? Then I remember `call_mmap_prepare`, and I see the crucial logic:
```c
if (desc->vm_file != map->file) {
map->file_doesnt_need_get = true;
map->file = desc->vm_file;
}
```
Aha! If `desc->vm_file` is changed to a user-space address by `vfs_mmap_prepare` or an implementation of `mmap_prepare`! That's it! I need to search for implementations of `mmap_prepare` where `desc->vm_file` is modified. I will search for `desc->vm_file =` or `vma_set_file` in the kernel source, specifically looking for `mmap_prepare` implementations. This should be the key to finding the root cause.
|
| 65/2 |
2026/05/23 11:08 |
tool |
grepper |
0m
Args: map[Expression:\->vm_file.*=]
Results: map[Output:arch/powerpc/mm/cacheflush.c=190=void copy_user_page(void *vto, void *vfrom, unsigned long vaddr,
--
arch/powerpc/mm/cacheflush.c-205-#if 0
arch/powerpc/mm/cacheflush.c:206: if (!vma->vm_file && ((vma->vm_flags & VM_EXEC) == 0))
arch/powerpc/mm/cacheflush.c-207- return;
--
arch/sparc/mm/fault_64.c=267=asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
--
arch/sparc/mm/fault_64.c-417- (vma->vm_flags & VM_EXEC) != 0 &&
arch/sparc/mm/fault_64.c:418: vma->vm_file != NULL)
arch/sparc/mm/fault_64.c-419- set_thread_fault_code(fault_code |
--
drivers/gpu/drm/i915/gem/i915_gem_mman.c=29=__vma_matches(struct vm_area_struct *vma, struct file *filp,
--
drivers/gpu/drm/i915/gem/i915_gem_mman.c-31-{
drivers/gpu/drm/i915/gem/i915_gem_mman.c:32: if (vma->vm_file != filp)
drivers/gpu/drm/i915/gem/i915_gem_mman.c-33- return false;
--
drivers/infiniband/core/ib_core_uverbs.c=71=int rdma_user_mmap_io(struct ib_ucontext *ucontext, struct vm_area_struct *vma,
--
drivers/infiniband/core/ib_core_uverbs.c-85- if (WARN_ON(!vma->vm_file ||
drivers/infiniband/core/ib_core_uverbs.c:86: vma->vm_file->private_data != ufile))
drivers/infiniband/core/ib_core_uverbs.c-87- return -EINVAL;
--
fs/coda/file.c=151=coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
--
fs/coda/file.c-200-
fs/coda/file.c:201: vma->vm_file = get_file(host_file);
fs/coda/file.c-202- ret = vfs_mmap(vma->vm_file, vma);
--
fs/coredump.c=1594=static unsigned long vma_dump_size(struct vm_area_struct *vma,
--
fs/coredump.c-1629- if (vma->vm_flags & VM_SHARED) {
fs/coredump.c:1630: if (file_inode(vma->vm_file)->i_nlink == 0 ?
fs/coredump.c-1631- FILTER(ANON_SHARED) : FILTER(MAPPED_SHARED))
--
fs/coredump.c-1638- goto whole;
fs/coredump.c:1639: if (vma->vm_file == NULL)
fs/coredump.c-1640- return 0;
--
fs/coredump.c-1650- vma->vm_pgoff == 0 && (vma->vm_flags & VM_READ)) {
fs/coredump.c:1651: if ((READ_ONCE(file_inode(vma->vm_file)->i_mode) & 0111) != 0)
fs/coredump.c-1652- return PAGE_SIZE;
--
fs/kernfs/file.c=457=static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
--
fs/kernfs/file.c-488- */
fs/kernfs/file.c:489: if (vma->vm_file != file)
fs/kernfs/file.c-490- goto out_put;
--
include/drm/drm_vma_manager.h=148=static inline void drm_vma_node_reset(struct drm_vma_offset_node *node)
--
include/drm/drm_vma_manager.h-150- memset(node, 0, sizeof(*node));
include/drm/drm_vma_manager.h:151: node->vm_files = RB_ROOT;
include/drm/drm_vma_manager.h-152- rwlock_init(&node->vm_lock);
--
ipc/shm.c=1728=long ksys_shmdt(char __user *shmaddr)
--
ipc/shm.c-1809- ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
ipc/shm.c:1810: (vma->vm_file == file)) {
ipc/shm.c-1811- do_vmi_align_munmap(&vmi, vma, mm, vma->vm_start,
--
kernel/events/uprobes.c=135=static bool valid_vma(struct vm_area_struct *vma, bool is_register)
--
kernel/events/uprobes.c-141-
kernel/events/uprobes.c:142: return vma->vm_file && (vma->vm_flags & flags) == VM_MAYEXEC;
kernel/events/uprobes.c-143-}
--
kernel/events/uprobes.c=279=static bool valid_ref_ctr_vma(struct uprobe *uprobe,
--
kernel/events/uprobes.c-285- vma->vm_file &&
kernel/events/uprobes.c:286: file_inode(vma->vm_file) == uprobe->inode &&
kernel/events/uprobes.c-287- (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
--
kernel/events/uprobes.c=1272=register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
--
kernel/events/uprobes.c-1304- if (!vma || !valid_vma(vma, is_register) ||
kernel/events/uprobes.c:1305: file_inode(vma->vm_file) != uprobe->inode)
kernel/events/uprobes.c-1306- goto unlock;
--
kernel/events/uprobes.c=1470=static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
--
kernel/events/uprobes.c-1481- if (!valid_vma(vma, false) ||
kernel/events/uprobes.c:1482: file_inode(vma->vm_file) != uprobe->inode)
kernel/events/uprobes.c-1483- continue;
--
kernel/sched/fair.c=3363=static void task_numa_work(struct callback_head *work)
--
kernel/sched/fair.c-3468- if (!vma->vm_mm ||
kernel/sched/fair.c:3469: (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ))) {
kernel/sched/fair.c-3470- trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_SHARED_RO);
--
mm/madvise.c=327=static inline bool can_do_file_pageout(struct vm_area_struct *vma)
--
mm/madvise.c-338- file_inode(vma->vm_file)) ||
mm/madvise.c:339: file_permission(vma->vm_file, MAY_WRITE) == 0;
mm/madvise.c-340-}
--
mm/mincore.c=218=static inline bool can_do_mincore(struct vm_area_struct *vma)
--
mm/mincore.c-231- file_inode(vma->vm_file)) ||
mm/mincore.c:232: file_permission(vma->vm_file, MAY_WRITE) == 0;
mm/mincore.c-233-}
--
mm/mmap.c=1085=SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
--
mm/mmap.c-1163- goto out;
mm/mmap.c:1164: if (vma->vm_file != file)
mm/mmap.c-1165- goto out;
--
mm/mmap.c-1175-
mm/mmap.c:1176: if (next->vm_file != vma->vm_file)
mm/mmap.c-1177- goto out;
--
mm/nommu.c=1012=unsigned long do_mmap(struct file *file,
--
mm/nommu.c-1063- if (file) {
mm/nommu.c:1064: region->vm_file = get_file(file);
mm/nommu.c:1065: vma->vm_file = get_file(file);
mm/nommu.c-1066- }
--
mm/nommu.c-1091- /* search for overlapping mappings on the same file */
mm/nommu.c:1092: if (file_inode(pregion->vm_file) !=
mm/nommu.c-1093- file_inode(file))
--
mm/rmap.c=856=unsigned long page_address_in_vma(const struct folio *folio,
--
mm/rmap.c-869- return -EFAULT;
mm/rmap.c:870: } else if (vma->vm_file->f_mapping != folio->mapping) {
mm/rmap.c-871- return -EFAULT;
--
mm/shmem.c=5932=int shmem_zero_setup(struct vm_area_struct *vma)
--
mm/shmem.c-5940- fput(vma->vm_file);
mm/shmem.c:5941: vma->vm_file = file;
mm/shmem.c-5942- vma->vm_ops = &shmem_anon_vm_ops;
--
mm/shmem.c=5953=int shmem_zero_setup_desc(struct vm_area_desc *desc)
--
mm/shmem.c-5959-
mm/shmem.c:5960: desc->vm_file = file;
mm/shmem.c-5961- desc->vm_ops = &shmem_anon_vm_ops;
--
mm/vma.c=86=static inline bool is_mergeable_vma(struct vma_merge_struct *vmg, bool merge_next)
--
mm/vma.c-93- return false;
mm/vma.c:94: if (vma->vm_file != vmg->file)
mm/vma.c-95- return false;
--
mm/vma.c=1774=static void unlink_file_vma_batch_process(struct unlink_vma_file_batch *vb)
--
mm/vma.c-1781- for (i = 0; i < vb->count; i++) {
mm/vma.c:1782: VM_WARN_ON_ONCE(vb->vmas[i]->vm_file->f_mapping != mapping);
mm/vma.c-1783- __remove_shared_vm_struct(vb->vmas[i], mapping);
--
mm/vma.c=1790=void unlink_file_vma_batch_add(struct unlink_vma_file_batch *vb,
--
mm/vma.c-1792-{
mm/vma.c:1793: if (vma->vm_file == NULL)
mm/vma.c-1794- return;
mm/vma.c-1795-
mm/vma.c:1796: if ((vb->count > 0 && vb->vmas[0]->vm_file != vma->vm_file) ||
mm/vma.c-1797- vb->count == ARRAY_SIZE(vb->vmas))
--
mm/vma.c=1951=static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
--
mm/vma.c-1954- mpol_equal(vma_policy(a), vma_policy(b)) &&
mm/vma.c:1955: a->vm_file == b->vm_file &&
mm/vma.c-1956- !((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | VM_IGNORE_MERGE)) &&
--
mm/vma.c=2367=static void set_desc_from_map(struct vm_area_desc *desc,
--
mm/vma.c-2373- desc->pgoff = map->pgoff;
mm/vma.c:2374: desc->vm_file = map->file;
mm/vma.c-2375- desc->vma_flags = map->vma_flags;
--
mm/vma.c=2455=static int __mmap_new_file_vma(struct mmap_state *map,
--
mm/vma.c-2460-
mm/vma.c:2461: vma->vm_file = map->file;
mm/vma.c-2462- if (!map->file_doesnt_need_get)
--
mm/vma.c-2472- fput(vma->vm_file);
mm/vma.c:2473: vma->vm_file = NULL;
mm/vma.c-2474-
--
mm/vma.c=2638=static int call_mmap_prepare(struct mmap_state *map,
--
mm/vma.c-2651- map->pgoff = desc->pgoff;
mm/vma.c:2652: if (desc->vm_file != map->file) {
mm/vma.c-2653- map->file_doesnt_need_get = true;
--
mm/vma.h=299=static inline void set_vma_from_desc(struct vm_area_struct *vma,
--
mm/vma.h-309- vma->vm_pgoff = desc->pgoff;
mm/vma.h:310: if (desc->vm_file != vma->vm_file)
mm/vma.h-311- vma_set_file(vma, desc->vm_file);
--
mm/vma_init.c=41=static void vm_area_init_from(const struct vm_area_struct *src,
--
mm/vma_init.c-49- dest->vm_pgoff = src->vm_pgoff;
mm/vma_init.c:50: dest->vm_file = src->vm_file;
mm/vma_init.c-51- dest->vm_private_data = src->vm_private_data;
]
|
| 66/2 |
2026/05/23 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 49195
output: 19
thoughts: 1354
Thoughts: **Analyzing the Memory Corruption Root Cause**
Okay, so `shmem_zero_setup_desc` sets `desc->vm_file = file`, which usually points to `/dev/zero` or anonymous mappings. But what if this `file` is actually a user-space address? Let's dig deeper, tracing the crash and the associated memory addresses.
The crash report gives me a KASAN error at `kasan_byte_accessible+0x12/0x30`, specifically trying to access memory using `0x0000000700000af0`. The `RDI` register contains `0x00000000e000015e`, which translates to the KASAN shadow address for `0x0000000700000af0`. This is a non-canonical address, confirming that KASAN is indeed checking this user-space address, `0x0000000700000af0`. This tells me the kernel is trying to touch that user-space memory region, which is a red flag. The relevant `mapping` value is `0x0000000700000900`, another user-space address, and I'm trying to figure out how *that* ended up in the kernel.
I know that `mapping` is read from `file->f_mapping`. So, if `file` is valid, then `file->f_mapping` must have been corrupted to `0x0000000700000900`. I have to consider the possibility of a use-after-free or out-of-bounds write on `struct file`. However, in the case of a block device file, `file->f_mapping` would point to the block device inode's mapping. Could the block device inode be corrupted instead? Or, could `file` itself be a user-space address? If `file` is `0x0000000700000870`, then reading `file->f_mapping` would trigger a KASAN on `0x0000000700000900`.
Here's the critical point. The crash happened *after* the read of `file->f_mapping`, when trying to access `mapping->i_mmap_rwsem`, i.e., `0x0000000700000af0`. This tells me that the read of `file->f_mapping` *succeeded*. If `file` had been a user-space pointer, reading `file->f_mapping` would have immediately triggered a KASAN violation on `0x0000000700000900`, which did *not* happen.
In the function `vma_link_file`, `file->f_mapping` is explicitly read. KASAN catches the crash when attempting to access `mapping->i_mmap_rwsem`. Thus, the corruption must be on `file->f_mapping`. How can `file->f_mapping` be overwritten with a user-space address? This points to a potential vulnerability in the file handling or block device code, where a valid kernel pointer's `f_mapping` field gets overwritten with a user-space address. The search for `f_mapping = ` in the kernel source code is now crucial.
|
| 67/2 |
2026/05/23 11:08 |
tool |
grepper |
0m
Args: map[Expression:f_mapping.*=]
Results: map[Output:block/bdev.c=942=int bdev_open(struct block_device *bdev, blk_mode_t mode, void *holder,
--
block/bdev.c-1004- bdev_file->f_mode |= FMODE_WRITE_RESTRICTED;
block/bdev.c:1005: bdev_file->f_mapping = bdev->bd_mapping;
block/bdev.c-1006- bdev_file->f_wb_err = filemap_sample_wb_err(bdev_file->f_mapping);
--
drivers/accel/drm_accel.c=117=int accel_open(struct inode *inode, struct file *filp)
--
drivers/accel/drm_accel.c-131- /* share address_space across all char-devs of a single device */
drivers/accel/drm_accel.c:132: filp->f_mapping = dev->anon_inode->i_mapping;
drivers/accel/drm_accel.c-133-
--
drivers/block/loop.c=483=static int loop_validate_file(struct file *file, struct block_device *bdev)
--
drivers/block/loop.c-492- lockdep_assert_held(&loop_validate_mutex);
drivers/block/loop.c:493: if (f->f_mapping->host->i_rdev == bdev->bd_dev)
drivers/block/loop.c-494- return -EBADF;
--
drivers/char/mem.c=616=static int open_port(struct inode *inode, struct file *filp)
--
drivers/char/mem.c-634- */
drivers/char/mem.c:635: filp->f_mapping = iomem_get_mapping();
drivers/char/mem.c-636-
--
drivers/dax/device.c=356=static int dax_open(struct inode *inode, struct file *filp)
--
drivers/dax/device.c-365- inode->i_mapping->a_ops = &dev_dax_aops;
drivers/dax/device.c:366: filp->f_mapping = inode->i_mapping;
drivers/dax/device.c-367- filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
--
drivers/gpu/drm/drm_file.c=369=int drm_open(struct inode *inode, struct file *filp)
--
drivers/gpu/drm/drm_file.c-385- /* share address_space across all char-devs of a single device */
drivers/gpu/drm/drm_file.c:386: filp->f_mapping = dev->anon_inode->i_mapping;
drivers/gpu/drm/drm_file.c-387-
--
drivers/gpu/drm/drm_file.c=1057=struct file *mock_drm_getfile(struct drm_minor *minor, unsigned int flags)
--
drivers/gpu/drm/drm_file.c-1073- /* Everyone shares a single global address space */
drivers/gpu/drm/drm_file.c:1074: file->f_mapping = dev->anon_inode->i_mapping;
drivers/gpu/drm/drm_file.c-1075-
--
drivers/gpu/drm/drm_prime.c=239=struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
--
drivers/gpu/drm/drm_prime.c-250- drm_gem_object_get(obj);
drivers/gpu/drm/drm_prime.c:251: dma_buf->file->f_mapping = obj->dev->anon_inode->i_mapping;
drivers/gpu/drm/drm_prime.c-252-
--
drivers/gpu/drm/i915/gem/i915_gem_mman.c=968=static struct file *mmap_singleton(struct drm_i915_private *i915)
--
drivers/gpu/drm/i915/gem/i915_gem_mman.c-980- /* Everyone shares a single global address space */
drivers/gpu/drm/i915/gem/i915_gem_mman.c:981: file->f_mapping = i915->drm.anon_inode->i_mapping;
drivers/gpu/drm/i915/gem/i915_gem_mman.c-982-
--
drivers/net/ethernet/mellanox/mlx4/main.c=1897=static int map_bf_area(struct mlx4_dev *dev)
--
drivers/net/ethernet/mellanox/mlx4/main.c-1910- (dev->caps.num_uars << PAGE_SHIFT);
drivers/net/ethernet/mellanox/mlx4/main.c:1911: priv->bf_mapping = io_mapping_create_wc(bf_start, bf_len);
drivers/net/ethernet/mellanox/mlx4/main.c-1912- if (!priv->bf_mapping)
--
drivers/pci/pci-sysfs.c=1033=void pci_create_legacy_files(struct pci_bus *b)
--
drivers/pci/pci-sysfs.c-1052- b->legacy_io->mmap = pci_mmap_legacy_io;
drivers/pci/pci-sysfs.c:1053: b->legacy_io->f_mapping = iomem_get_mapping;
drivers/pci/pci-sysfs.c-1054- pci_adjust_legacy_attr(b, pci_mmap_io);
--
drivers/pci/pci-sysfs.c-1067- b->legacy_mem->llseek = pci_llseek_resource;
drivers/pci/pci-sysfs.c:1068: b->legacy_mem->f_mapping = iomem_get_mapping;
drivers/pci/pci-sysfs.c-1069- pci_adjust_legacy_attr(b, pci_mmap_mem);
--
drivers/pci/pci-sysfs.c=1234=static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
--
drivers/pci/pci-sysfs.c-1263- if (res_attr->mmap) {
drivers/pci/pci-sysfs.c:1264: res_attr->f_mapping = iomem_get_mapping;
drivers/pci/pci-sysfs.c-1265- /*
--
drivers/pci/proc.c=298=static int proc_bus_pci_open(struct inode *inode, struct file *file)
--
drivers/pci/proc.c-308- file->private_data = fpriv;
drivers/pci/proc.c:309: file->f_mapping = iomem_get_mapping();
drivers/pci/proc.c-310-
--
drivers/vfio/device_cdev.c=23=int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
--
drivers/vfio/device_cdev.c-46- */
drivers/vfio/device_cdev.c:47: filep->f_mapping = device->inode->i_mapping;
drivers/vfio/device_cdev.c-48-
--
drivers/vfio/group.c=250=static struct file *vfio_device_open_file(struct vfio_device *device)
--
drivers/vfio/group.c-278- */
drivers/vfio/group.c:279: filep->f_mapping = device->inode->i_mapping;
drivers/vfio/group.c-280-
--
drivers/video/fbdev/core/fb_defio.c=326=void fb_deferred_io_open(struct fb_info *info,
--
drivers/video/fbdev/core/fb_defio.c-332- fbdefio->mapping = file->f_mapping;
drivers/video/fbdev/core/fb_defio.c:333: file->f_mapping->a_ops = &fb_deferred_io_aops;
drivers/video/fbdev/core/fb_defio.c-334- fbdefio->open_count++;
--
fs/anon_inodes.c=134=static struct file *__anon_inode_getfile(const char *name,
--
fs/anon_inodes.c-170-
fs/anon_inodes.c:171: file->f_mapping = inode->i_mapping;
fs/anon_inodes.c-172-
--
fs/coda/file.c=151=coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
--
fs/coda/file.c-183- spin_lock(&cii->c_lock);
fs/coda/file.c:184: coda_file->f_mapping = host_file->f_mapping;
fs/coda/file.c-185- if (coda_inode->i_mapping == &coda_inode->i_data)
--
fs/erofs/ishare.c=102=static int erofs_ishare_file_open(struct inode *inode, struct file *file)
--
fs/erofs/ishare.c-114- realfile->f_inode = sharedinode;
fs/erofs/ishare.c:115: realfile->f_mapping = sharedinode->i_mapping;
fs/erofs/ishare.c-116- path_get(&file->f_path);
--
fs/fcntl.c=369=static long fcntl_set_rw_hint(struct file *file, unsigned long arg)
--
fs/fcntl.c-388- */
fs/fcntl.c:389: if (file->f_mapping->host != inode)
fs/fcntl.c-390- WRITE_ONCE(file->f_mapping->host->i_write_hint, hint);
--
fs/file_table.c=154=static int init_file(struct file *f, int flags, const struct cred *cred)
--
fs/file_table.c-185- f->f_op = NULL;
fs/file_table.c:186: f->f_mapping = NULL;
fs/file_table.c-187- f->private_data = NULL;
--
fs/file_table.c=320=static void file_init_path(struct file *file, const struct path *path,
--
fs/file_table.c-324- file->f_inode = path->dentry->d_inode;
fs/file_table.c:325: file->f_mapping = path->dentry->d_inode->i_mapping;
fs/file_table.c-326- file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
--
fs/file_table.c=428=struct file *alloc_file_clone(struct file *base, int flags,
--
fs/file_table.c-435- path_get(&f->f_path);
fs/file_table.c:436: f->f_mapping = base->f_mapping;
fs/file_table.c-437- }
--
fs/open.c=887=static int do_dentry_open(struct file *f,
--
fs/open.c-895- f->f_inode = inode;
fs/open.c:896: f->f_mapping = inode->i_mapping;
fs/open.c-897- f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
--
fs/sysfs/file.c=188=static int sysfs_kf_bin_open(struct kernfs_open_file *of)
--
fs/sysfs/file.c-192- if (battr->f_mapping)
fs/sysfs/file.c:193: of->file->f_mapping = battr->f_mapping();
fs/sysfs/file.c-194-
--
mm/rmap.c=856=unsigned long page_address_in_vma(const struct folio *folio,
--
mm/rmap.c-869- return -EFAULT;
mm/rmap.c:870: } else if (vma->vm_file->f_mapping != folio->mapping) {
mm/rmap.c-871- return -EFAULT;
--
mm/swapfile.c=2769=SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
--
mm/swapfile.c-2794- if (p->flags & SWP_WRITEOK) {
mm/swapfile.c:2795: if (p->swap_file->f_mapping == mapping) {
mm/swapfile.c-2796- found = 1;
--
mm/vma.c=1774=static void unlink_file_vma_batch_process(struct unlink_vma_file_batch *vb)
--
mm/vma.c-1781- for (i = 0; i < vb->count; i++) {
mm/vma.c:1782: VM_WARN_ON_ONCE(vb->vmas[i]->vm_file->f_mapping != mapping);
mm/vma.c-1783- __remove_shared_vm_struct(vb->vmas[i], mapping);
--
net/ceph/osd_client.c=1217=static void osd_init(struct ceph_osd *osd)
--
net/ceph/osd_client.c-1223- osd->o_linger_requests = RB_ROOT;
net/ceph/osd_client.c:1224: osd->o_backoff_mappings = RB_ROOT;
net/ceph/osd_client.c-1225- osd->o_backoffs_by_id = RB_ROOT;
]
|
| 68/2 |
2026/05/23 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 55056
output: 45
thoughts: 5248
Thoughts: **Analyzing a Potential Kernel Memory Corruption**
Okay, I'm diving deep into this `f_mapping` issue. It seems like the `coda_file_mmap` function can modify a file's `f_mapping`, which is the starting point. I need to be sure that modification isn't unexpected. Now, I'm thinking about loop devices and how their `f_mapping` might be handled differently, especially in relation to the `struct file`. The core question is: could a file be freed and then reallocated with user-controlled `f_mapping`?
I need to understand if `f_mapping` is ever overwritten in a way that could lead to a user-space address being used when it shouldn't be. The `vma->vm_file` variable is what I need to look at because it has a reference count, which is important. But what if the `vma->vm_file` isn't a block device file? What if it's a file that was closed, but the VMA still has a reference? Can `mmap_prepare` somehow change the `file` to point to a freed file?
Now, the `shmem_zero_setup_desc` routine is interesting; I need to find all the places `desc->vm_file` changes. It looks like `shmem_zero_setup_desc` can set `desc->vm_file` to a new file, but not for block devices. A variable not being initialized is always a possibility. Digging through `__mmap_region` code, `desc.vm_file` is initialized to `NULL` but is later set to `map->file`. Now, I need to know where `map->file` can be changed.
The `vfs_mmap_prepare` function is a key; if it doesn't change `desc->vm_file`, it remains `map->file`. The call to `call_mmap_prepare` is the crucial spot. If `desc->vm_file != map->file`, the former becomes the new `map->file`. Okay, if `map->file` is `NULL`, then `call_mmap_prepare` is not called, because `have_mmap_prepare` will be false.
So, `file` comes from `fget(fd)` or `hugetlb_file_setup`, both of which should give me a valid kernel pointer. This implies that `map->file` and `vma->vm_file` are valid kernel pointers. However, I am trying to figure out how `file->f_mapping` can be a user-space address. This would result in reading a user-space address and causing a crash. It all comes back to how `vma->vm_file` is set, namely from `map->file`. So it looks like `map->file` must be a user-space address at some point. It is initialized to `file`, the argument to `__mmap_region`.
`do_mmap` eventually calls `ksys_mmap_pgoff`. It obtains `file` from `fget(fd)` or `hugetlb_file_setup`, and it should be a valid kernel pointer. If `file->f_mapping` is a user-space address, the kernel would crash when reading it. The `file` pointer has to be valid, but I'm thinking the `f_mapping` field could be overwritten. The offset of `f_mapping` is known; it's at 0x90 in `struct file`. The `struct file` might be freed, reallocated, and have a user-controlled `f_mapping`. However, `file` has a reference count, and `fget(fd)` increments the count.
Now, checking the `__mmap_new_file_vma` function, it does `get_file(map->file)` and it calls `mmap_file`. Now the problem is if `map->file_doesnt_need_get` is true, it doesn't call `get_file()`. This is only set if `vfs_mmap_prepare` changes `desc->vm_file`. If it changes `desc->vm_file`, it's assumed the new file has an elevated reference count. However, what if `vfs_mmap_prepare` does NOT change `desc->vm_file` and `map->file_doesnt_need_get` is already true?
Now, in `__mmap_new_file_vma`, if it calls `mmap_file` and it returns an error, there is an `fput(vma->vm_file)`. What if `vma->vm_file` is
|
| 69/2 |
2026/05/23 11:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/vma.c IncludeLines:true Name:set_vma_user_defined_fields]
Results: map[SourceCode:2665: static void set_vma_user_defined_fields(struct vm_area_struct *vma,
2666: struct mmap_state *map)
2667: {
2668: if (map->vm_ops)
2669: vma->vm_ops = map->vm_ops;
2670: vma->vm_private_data = map->vm_private_data;
2671: }
SourceFile:mm/vma.c]
|
| 70/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 61523
output: 43
thoughts: 884
Thoughts: **Analyzing a Potential Kernel Crash in mmap Implementation**
Okay, so `vma->vm_ops` *is* set, that's good. But here's a potential issue: if `map->file->f_op->mmap` is NULL, then `__mmap_new_file_vma` returns 0. I have to trace through. If this happens, `__mmap_region` continues, checks for `have_mmap_prepare` and then there's this call to `set_vma_user_defined_fields`.
What if `map->file->f_op->mmap` is actually NULL, but `have_mmap_prepare` is true? In that case, `__mmap_new_file_vma` still returns 0, and then `vma_link_file` is called within `__mmap_new_vma`! The interesting thing is that `vma_link_file` is called *before* `set_vma_user_defined_fields`! So this is going to be important.
Looking at `__mmap_region` itself: If `!vma` the code goes to `__mmap_new_vma` which calls `vma_link_file(vma, map->hold_file_rmap_lock)`. Okay, so `vma_link_file` uses `vma->vm_file`. I see it clearly here. So `vma->vm_file` points to some `file` which has a backing `mapping`.
Okay, this looks fine. `vma->vm_file` is set to `map->file` in `__mmap_new_file_vma`. And `map->file` is, supposedly, the block device file. Therefore, `mapping` should be the block device file's `f_mapping`. So, why is this crashing?
Wait! What if `map->file->f_op->mmap` is NULL, but `map->file` is NOT the original file? What if `map->file` was changed by `call_mmap_prepare`? But we've established that `blkdev_mmap_prepare` does *not* change `desc->vm_file`, so `map->file` should indeed be the block device file.
Ah, wait, the bug report... What if `file` is *not* a block device file? What if `file` is a loop device backing file? But... wait, `mmap` is *called* on the loop device, which *is* a block device, isn't it? The bug report states: "loop1: detected capacity change from 0 to 32768". This points to something changing, like `loop_set_status` or `loop_configure`. Could it be that the loop device's `f_mapping` is changed? Let me go back and re-examine `loop_configure`. And specifically, `loop_assign_backing_file`. I need to look closer at what happens there...
|
| 71/2 |
2026/05/23 11:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/block/loop.c IncludeLines:true Name:loop_assign_backing_file]
Results: map[SourceCode: 508: static void loop_assign_backing_file(struct loop_device *lo, struct file *file)
509: {
510: lo->lo_backing_file = file;
511: lo->old_gfp_mask = mapping_gfp_mask(file->f_mapping);
512: mapping_set_gfp_mask(file->f_mapping,
513: lo->old_gfp_mask & ~(__GFP_IO | __GFP_FS));
514: if (lo->lo_backing_file->f_flags & O_DIRECT)
515: lo->lo_flags |= LO_FLAGS_DIRECT_IO;
516: lo->lo_min_dio_size = loop_query_min_dio_size(lo);
517: }
SourceFile:drivers/block/loop.c]
|
| 72/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 63366
output: 46
thoughts: 452
Thoughts: **Analyzing a Potential Kernel Bug**
Okay, so I'm trying to figure out what's causing this crash, and my initial train of thought was focused on how block device mappings are handled. It seems like the bug *isn't* directly related to the `f_mapping` field of the file itself, which simplifies things. But, what if there's a change to the block device's underlying inode mapping (`bd_inode->i_mapping`)? I should probably check `bdev_file->f_mapping` to be sure. When a block device is opened, the file's mapping (`bdev_file->f_mapping`) seems to be set to the block device's mapping (`bdev->bd_mapping`).
The next question is, does `bdev->bd_mapping` *ever* get modified? It doesn't seem like it, it points to `bdev->bd_inode->i_mapping`. So, is there an edge case around freeing the block device? What happens if the block device is closed and the resources are freed?
If the block device *is* freed, then `bdev->bd_inode` also goes away. But wait, isn't the file still holding a reference to the block device? And indeed, `bdev_file` does hold a reference to `bdev`, so the block device *can't* be freed.
But hold on, this "loop1: detected capacity change..." log message might be a red herring! Maybe this isn't related to the loop device at all. The crash could be happening in a completely different part of the code!
Right, let's look at the crash dump. It's in `kasan_byte_accessible`, which is called from `__kasan_check_byte`, then `lock_acquire`, then `_raw_spin_lock`, and finally `task_blocks_on_rt_mutex`.
Aha! `task_blocks_on_rt_mutex`! That implies the lock is *contended*! If it's contended, it's trying to block on an `rt_mutex`.
The crash is in `task_blocks_on_rt_mutex` -> `__rt_mutex_slowlock_locked` -> `__rt_mutex_slowlock` -> `rt_mutex_slowlock` -> `__rt_mutex_lock` -> `rwbase_write_lock` -> `i_mmap_lock_write`.
Wait, the crash isn't happening while reading `mapping->i_mmap_rwsem`. The problem is within `task_blocks_on_rt_mutex` itself. I need to focus on what happens in there. Let's dig into `task_blocks_on_rt_mutex` and see what it is doing.
|
| 73/2 |
2026/05/23 11:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/rtmutex.c IncludeLines:true Name:task_blocks_on_rt_mutex]
Results: map[SourceCode:1196: /*
1197: * Task blocks on lock.
1198: *
1199: * Prepare waiter and propagate pi chain
1200: *
1201: * This must be called with lock->wait_lock held and interrupts disabled
1202: */
1203: static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
1204: struct rt_mutex_waiter *waiter,
1205: struct task_struct *task,
1206: struct ww_acquire_ctx *ww_ctx,
1207: enum rtmutex_chainwalk chwalk,
1208: struct wake_q_head *wake_q)
1209: {
1210: struct task_struct *owner = rt_mutex_owner(lock);
1211: struct rt_mutex_waiter *top_waiter = waiter;
1212: struct rt_mutex_base *next_lock;
1213: int chain_walk = 0, res;
1214:
1215: lockdep_assert_held(&lock->wait_lock);
1216:
1217: /*
1218: * Early deadlock detection. We really don't want the task to
1219: * enqueue on itself just to untangle the mess later. It's not
1220: * only an optimization. We drop the locks, so another waiter
1221: * can come in before the chain walk detects the deadlock. So
1222: * the other will detect the deadlock and return -EDEADLOCK,
1223: * which is wrong, as the other waiter is not in a deadlock
1224: * situation.
1225: *
1226: * Except for ww_mutex, in that case the chain walk must already deal
1227: * with spurious cycles, see the comments at [3] and [6].
1228: */
1229: if (owner == task && !(build_ww_mutex() && ww_ctx))
1230: return -EDEADLK;
1231:
1232: raw_spin_lock(&task->pi_lock);
1233: waiter->task = task;
1234: waiter->lock = lock;
1235: waiter_update_prio(waiter, task);
1236: waiter_clone_prio(waiter, task);
1237:
1238: /* Get the top priority waiter on the lock */
1239: if (rt_mutex_has_waiters(lock))
1240: top_waiter = rt_mutex_top_waiter(lock);
1241: rt_mutex_enqueue(lock, waiter);
1242:
1243: task->pi_blocked_on = waiter;
1244:
1245: raw_spin_unlock(&task->pi_lock);
1246:
1247: if (build_ww_mutex() && ww_ctx) {
1248: struct rt_mutex *rtm;
1249:
1250: /* Check whether the waiter should back out immediately */
1251: rtm = container_of(lock, struct rt_mutex, rtmutex);
1252: res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, wake_q);
1253: if (res) {
1254: raw_spin_lock(&task->pi_lock);
1255: rt_mutex_dequeue(lock, waiter);
1256: task->pi_blocked_on = NULL;
1257: raw_spin_unlock(&task->pi_lock);
1258: return res;
1259: }
1260: }
1261:
1262: if (!owner)
1263: return 0;
1264:
1265: raw_spin_lock(&owner->pi_lock);
1266: if (waiter == rt_mutex_top_waiter(lock)) {
1267: rt_mutex_dequeue_pi(owner, top_waiter);
1268: rt_mutex_enqueue_pi(owner, waiter);
1269:
1270: rt_mutex_adjust_prio(lock, owner);
1271: if (owner->pi_blocked_on)
1272: chain_walk = 1;
1273: } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1274: chain_walk = 1;
1275: }
1276:
1277: /* Store the lock on which owner is blocked or NULL */
1278: next_lock = task_blocked_on_lock(owner);
1279:
1280: raw_spin_unlock(&owner->pi_lock);
1281: /*
1282: * Even if full deadlock detection is on, if the owner is not
1283: * blocked itself, we can avoid finding this out in the chain
1284: * walk.
1285: */
1286: if (!chain_walk || !next_lock)
1287: return 0;
1288:
1289: /*
1290: * The owner can't disappear while holding a lock,
1291: * so the owner struct is protected by wait_lock.
1292: * Gets dropped in rt_mutex_adjust_prio_chain()!
1293: */
1294: get_task_struct(owner);
1295:
1296: raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);
1297:
1298: res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1299: next_lock, waiter, task);
1300:
1301: raw_spin_lock_irq(&lock->wait_lock);
1302:
1303: return res;
1304: }
SourceFile:kernel/locking/rtmutex.c]
|
| 74/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 66163
output: 42
thoughts: 231
Thoughts: **Debugging a Kernel Spinlock Crash**
Okay, so the crash is happening within `_raw_spin_lock`, specifically called from `task_blocks_on_rt_mutex`. Hmm, `task_blocks_on_rt_mutex` calls `raw_spin_lock(&task->pi_lock)` and `raw_spin_lock(&owner->pi_lock)`. So the core of the problem *has* to be in that spinlock. The crash is undeniably in `_raw_spin_lock`. I need to figure out the memory access causing the issue.
Aha! If `owner` is some user-space address, then trying to lock `&owner->pi_lock` will try to access user-space memory from kernel mode, which, of course, is a big no-no and thatβs a likely culprit for the crash. Now, where is `owner` coming from? Let me seeβ¦ it's `rt_mutex_owner(lock)`.
```c
struct task_struct *owner = rt_mutex_owner(lock);
```
Okay, so `owner` is derived from `lock`. If `lock` is actually a user-space address, then the problem is clearly `rt_mutex_owner` is reading from user-space! This explains everything! Letβs confirm this. For example, if `lock` is `mapping->i_mmap_rwsem`, and `mapping` itself is a user-space pointer, then `lock` will be a user-space address! Thus, `rt_mutex_owner(lock)` would have to read from user-space, which explains the crash. I should investigate `rt_mutex_owner` function to confirm this suspicion.
|
| 75/2 |
2026/05/23 11:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/rtmutex.c IncludeLines:true Name:rt_mutex_owner]
Results: map[SourceCode: 50: static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
51: {
52: unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
53:
54: return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
55: }
SourceFile:include/linux/rtmutex.h]
|
| 76/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 66936
output: 21
thoughts: 598
Thoughts: **Debugging a KASAN Crash: A Deep Dive**
Okay, so I'm looking at this KASAN report, and my initial thought was, "Aha! `READ_ONCE(lock->owner)` is reading from a user-space address, and that's the problem!" I mean, if `lock` is a user-space address, then `READ_ONCE` should absolutely be triggering KASAN on `lock->owner`. But wait a minute⦠why did KASAN catch `raw_spin_lock(&owner->pi_lock)` instead? That's not what I expected. The crash happens in `lock_acquire`, which is called from `_raw_spin_lock`, so let's look at the stack trace.
Right, the trace shows the crash is in `kernel/locking/rtmutex.c` at line 1265, specifically: `raw_spin_lock(&owner->pi_lock);`. If `lock` *were* a user-space address, shouldn't `READ_ONCE(lock->owner)` have crashed first? The fact that it didn't makes me think `lock` isn't actually a user-space address. The key realization is that `READ_ONCE(lock->owner)` *succeeded*. Therefore, the assumption that `lock` was a user-space address is wrong.
If `lock` *isn't* a user-space address, then `mapping` also *isn't* a user-space address, because its value is dependent on `lock`. Okay, if `lock` is a valid kernel address, then `mapping` is valid too! That means the read of `lock->owner` was successful. So, where does `owner` come from? It's `rt_mutex_owner(lock)`. If `owner` is a *user-space* address, then `lock->owner` would have to contain a user-space address!
Hold on⦠`lock->owner` contained `0x0000000700000af0`? Okay, let me confirm the fault address: `0x0000000700000af0`. If `owner` is that address minus the offset of `pi_lock` within `struct task_struct`⦠well then we're getting closer. To understand this, I need to check the layout of `struct task_struct`. That should reveal the true source of this issue.
|
| 77/2 |
2026/05/23 11:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:thread_info OffsetBits:0 SizeBits:192] map[Name:__state OffsetBits:192 SizeBits:32] map[Name:saved_state OffsetBits:224 SizeBits:32] map[Name:stack OffsetBits:256 SizeBits:64] map[Name:usage OffsetBits:320 SizeBits:32] map[Name:flags OffsetBits:352 SizeBits:32] map[Name:ptrace OffsetBits:384 SizeBits:32] map[Name:on_cpu OffsetBits:416 SizeBits:32] map[Name:wake_entry OffsetBits:448 SizeBits:128] map[Name:wakee_flips OffsetBits:576 SizeBits:32] map[Name:wakee_flip_decay_ts OffsetBits:640 SizeBits:64] map[Name:last_wakee OffsetBits:704 SizeBits:64] map[Name:recent_used_cpu OffsetBits:768 SizeBits:32] map[Name:wake_cpu OffsetBits:800 SizeBits:32] map[Name:on_rq OffsetBits:832 SizeBits:32] map[Name:prio OffsetBits:864 SizeBits:32] map[Name:static_prio OffsetBits:896 SizeBits:32] map[Name:normal_prio OffsetBits:928 SizeBits:32] map[Name:rt_priority OffsetBits:960 SizeBits:32] map[Name:se OffsetBits:1024 SizeBits:2560] map[Name:rt OffsetBits:3584 SizeBits:384] map[Name:dl OffsetBits:3968 SizeBits:1920] map[Name:dl_server OffsetBits:5888 SizeBits:64] map[Name:sched_class OffsetBits:5952 SizeBits:64] map[Name:core_node OffsetBits:6016 SizeBits:192] map[Name:core_cookie OffsetBits:6208 SizeBits:64] map[Name:core_occupation OffsetBits:6272 SizeBits:32] map[Name:sched_task_group OffsetBits:6336 SizeBits:64] map[Name:sched_throttle_work OffsetBits:6400 SizeBits:128] map[Name:throttle_node OffsetBits:6528 SizeBits:128] map[Name:throttled OffsetBits:6656 SizeBits:8] map[Name:stats OffsetBits:7168 SizeBits:2048] map[Name:preempt_notifiers OffsetBits:9216 SizeBits:64] map[Name:btrace_seq OffsetBits:9280 SizeBits:32] map[Name:policy OffsetBits:9312 SizeBits:32] map[Name:max_allowed_capacity OffsetBits:9344 SizeBits:64] map[Name:nr_cpus_allowed OffsetBits:9408 SizeBits:32] map[Name:cpus_ptr OffsetBits:9472 SizeBits:64] map[Name:user_cpus_ptr OffsetBits:9536 SizeBits:64] map[Name:cpus_mask OffsetBits:9600 SizeBits:64] map[Name:migration_pending OffsetBits:9664 SizeBits:64] map[Name:migration_disabled OffsetBits:9728 SizeBits:16] map[Name:migration_flags OffsetBits:9744 SizeBits:16] map[Name:rcu_read_lock_nesting OffsetBits:9760 SizeBits:32] map[Name:rcu_read_unlock_special OffsetBits:9792 SizeBits:32] map[Name:rcu_node_entry OffsetBits:9856 SizeBits:128] map[Name:rcu_blocked_node OffsetBits:9984 SizeBits:64] map[Name:rcu_tasks_nvcsw OffsetBits:10048 SizeBits:64] map[Name:rcu_tasks_holdout OffsetBits:10112 SizeBits:8] map[Name:rcu_tasks_idx OffsetBits:10120 SizeBits:8] map[Name:rcu_tasks_idle_cpu OffsetBits:10144 SizeBits:32] map[Name:rcu_tasks_holdout_list OffsetBits:10176 SizeBits:128] map[Name:rcu_tasks_exit_cpu OffsetBits:10304 SizeBits:32] map[Name:rcu_tasks_exit_list OffsetBits:10368 SizeBits:128] map[Name:trc_reader_nesting OffsetBits:10496 SizeBits:32] map[Name:trc_reader_scp OffsetBits:10560 SizeBits:64] map[Name:sched_info OffsetBits:10624 SizeBits:512] map[Name:tasks OffsetBits:11136 SizeBits:128] map[Name:pushable_tasks OffsetBits:11264 SizeBits:320] map[Name:pushable_dl_tasks OffsetBits:11584 SizeBits:192] map[Name:mm OffsetBits:11776 SizeBits:64] map[Name:active_mm OffsetBits:11840 SizeBits:64] map[Name:exit_state OffsetBits:11904 SizeBits:32] map[Name:exit_code OffsetBits:11936 SizeBits:32] map[Name:exit_signal OffsetBits:11968 SizeBits:32] map[Name:pdeath_signal OffsetBits:12000 SizeBits:32] map[Name:jobctl OffsetBits:12032 SizeBits:64] map[Name:personality OffsetBits:12096 SizeBits:32] map[Name:sched_reset_on_fork OffsetBits:12128 SizeBits:1] map[Name:sched_contributes_to_load OffsetBits:12129 SizeBits:1] map[Name:sched_migrated OffsetBits:12130 SizeBits:1] map[Name:sched_task_hot OffsetBits:12131 SizeBits:1] map[Name: OffsetBits:12160 SizeBits:0] map[Name:sched_remote_wakeup OffsetBits:12160 SizeBits:1] map[Name:sched_rt_mutex OffsetBits:12161 SizeBits:1] map[Name:in_execve OffsetBits:12162 SizeBits:1] map[Name:in_iowait OffsetBits:12163 SizeBits:1] map[Name:restore_sigmask OffsetBits:12164 SizeBits:1] map[Name:in_user_fault OffsetBits:12165 SizeBits:1] map[Name:no_cgroup_migration OffsetBits:12166 SizeBits:1] map[Name:frozen OffsetBits:12167 SizeBits:1] map[Name:use_memdelay OffsetBits:12168 SizeBits:1] map[Name:in_memstall OffsetBits:12169 SizeBits:1] map[Name:in_page_owner OffsetBits:12170 SizeBits:1] map[Name:in_eventfd OffsetBits:12171 SizeBits:1] map[Name:pasid_activated OffsetBits:12172 SizeBits:1] map[Name:reported_split_lock OffsetBits:12173 SizeBits:1] map[Name:in_thrashing OffsetBits:12174 SizeBits:1] map[Name:in_nf_duplicate OffsetBits:12175 SizeBits:1] map[Name:net_xmit OffsetBits:12224 SizeBits:384] map[Name:atomic_flags OffsetBits:12608 SizeBits:64] map[Name:restart_block OffsetBits:12672 SizeBits:448] map[Name:pid OffsetBits:13120 SizeBits:32] map[Name:tgid OffsetBits:13152 SizeBits:32] map[Name:stack_canary OffsetBits:13184 SizeBits:64] map[Name:real_parent OffsetBits:13248 SizeBits:64] map[Name:parent OffsetBits:13312 SizeBits:64] map[Name:children OffsetBits:13376 SizeBits:128] map[Name:sibling OffsetBits:13504 SizeBits:128] map[Name:group_leader OffsetBits:13632 SizeBits:64] map[Name:ptraced OffsetBits:13696 SizeBits:128] map[Name:ptrace_entry OffsetBits:13824 SizeBits:128] map[Name:thread_pid OffsetBits:13952 SizeBits:64] map[Name:pid_links OffsetBits:14016 SizeBits:512] map[Name:thread_node OffsetBits:14528 SizeBits:128] map[Name:vfork_done OffsetBits:14656 SizeBits:64] map[Name:set_child_tid OffsetBits:14720 SizeBits:64] map[Name:clear_child_tid OffsetBits:14784 SizeBits:64] map[Name:worker_private OffsetBits:14848 SizeBits:64] map[Name:utime OffsetBits:14912 SizeBits:64] map[Name:stime OffsetBits:14976 SizeBits:64] map[Name:gtime OffsetBits:15040 SizeBits:64] map[Name:prev_cputime OffsetBits:15104 SizeBits:640] map[Name:vtime OffsetBits:15744 SizeBits:704] map[Name:nvcsw OffsetBits:16448 SizeBits:64] map[Name:nivcsw OffsetBits:16512 SizeBits:64] map[Name:start_time OffsetBits:16576 SizeBits:64] map[Name:start_boottime OffsetBits:16640 SizeBits:64] map[Name:min_flt OffsetBits:16704 SizeBits:64] map[Name:maj_flt OffsetBits:16768 SizeBits:64] map[Name:posix_cputimers OffsetBits:16832 SizeBits:640] map[Name:posix_cputimers_work OffsetBits:17472 SizeBits:1216] map[Name:ptracer_cred OffsetBits:18688 SizeBits:64] map[Name:real_cred OffsetBits:18752 SizeBits:64] map[Name:cred OffsetBits:18816 SizeBits:64] map[Name:cached_requested_key OffsetBits:18880 SizeBits:64] map[Name:comm OffsetBits:18944 SizeBits:128] map[Name:nameidata OffsetBits:19072 SizeBits:64] map[Name:sysvsem OffsetBits:19136 SizeBits:64] map[Name:sysvshm OffsetBits:19200 SizeBits:128] map[Name:last_switch_count OffsetBits:19328 SizeBits:64] map[Name:last_switch_time OffsetBits:19392 SizeBits:64] map[Name:fs OffsetBits:19456 SizeBits:64] map[Name:files OffsetBits:19520 SizeBits:64] map[Name:io_uring OffsetBits:19584 SizeBits:64] map[Name:io_uring_restrict OffsetBits:19648 SizeBits:64] map[Name:nsproxy OffsetBits:19712 SizeBits:64] map[Name:signal OffsetBits:19776 SizeBits:64] map[Name:sighand OffsetBits:19840 SizeBits:64] map[Name:blocked OffsetBits:19904 SizeBits:64] map[Name:real_blocked OffsetBits:19968 SizeBits:64] map[Name:saved_sigmask OffsetBits:20032 SizeBits:64] map[Name:pending OffsetBits:20096 SizeBits:192] map[Name:sas_ss_sp OffsetBits:20288 SizeBits:64] map[Name:sas_ss_size OffsetBits:20352 SizeBits:64] map[Name:sas_ss_flags OffsetBits:20416 SizeBits:32] map[Name:task_works OffsetBits:20480 SizeBits:64] map[Name:audit_context OffsetBits:20544 SizeBits:64] map[Name:loginuid OffsetBits:20608 SizeBits:32] map[Name:sessionid OffsetBits:20640 SizeBits:32] map[Name:seccomp OffsetBits:20672 SizeBits:128] map[Name:syscall_dispatch OffsetBits:20800 SizeBits:256] map[Name:parent_exec_id OffsetBits:21056 SizeBits:64] map[Name:self_exec_id OffsetBits:21120 SizeBits:64] map[Name:alloc_lock OffsetBits:21184 SizeBits:1024] map[Name:pi_lock OffsetBits:22208 SizeBits:512] map[Name:wake_q OffsetBits:22720 SizeBits:64] map[Name:pi_waiters OffsetBits:22784 SizeBits:128] map[Name:pi_top_task OffsetBits:22912 SizeBits:64] map[Name:pi_blocked_on OffsetBits:22976 SizeBits:64] map[Name:blocked_on OffsetBits:23040 SizeBits:64] map[Name:non_block_count OffsetBits:23104 SizeBits:32] map[Name:irqtrace OffsetBits:23168 SizeBits:448] map[Name:hardirq_threaded OffsetBits:23616 SizeBits:32] map[Name:hardirq_chain_key OffsetBits:23680 SizeBits:64] map[Name:softirqs_enabled OffsetBits:23744 SizeBits:32] map[Name:softirq_context OffsetBits:23776 SizeBits:32] map[Name:irq_config OffsetBits:23808 SizeBits:32] map[Name:softirq_disable_cnt OffsetBits:23840 SizeBits:32] map[Name:curr_chain_key OffsetBits:23872 SizeBits:64] map[Name:lockdep_depth OffsetBits:23936 SizeBits:32] map[Name:lockdep_recursion OffsetBits:23968 SizeBits:32] map[Name:held_locks OffsetBits:24000 SizeBits:15360] map[Name:in_ubsan OffsetBits:39360 SizeBits:32] map[Name:journal_info OffsetBits:39424 SizeBits:64] map[Name:bio_list OffsetBits:39488 SizeBits:64] map[Name:plug OffsetBits:39552 SizeBits:64] map[Name:reclaim_state OffsetBits:39616 SizeBits:64] map[Name:io_context OffsetBits:39680 SizeBits:64] map[Name:capture_control OffsetBits:39744 SizeBits:64] map[Name:ptrace_message OffsetBits:39808 SizeBits:64] map[Name:last_siginfo OffsetBits:39872 SizeBits:64] map[Name:ioac OffsetBits:39936 SizeBits:448] map[Name:psi_flags OffsetBits:40384 SizeBits:32] map[Name:acct_rss_mem1 OffsetBits:40448 SizeBits:64] map[Name:acct_vm_mem1 OffsetBits:40512 SizeBits:64] map[Name:acct_timexpd OffsetBits:40576 SizeBits:64] map[Name:mems_allowed OffsetBits:40640 SizeBits:64] map[Name:mems_allowed_seq OffsetBits:40704 SizeBits:448] map[Name:cpuset_mem_spread_rotor OffsetBits:41152 SizeBits:32] map[Name:cgroups OffsetBits:41216 SizeBits:64] map[Name:cg_list OffsetBits:41280 SizeBits:128] map[Name:cg_dead_lnode OffsetBits:41408 SizeBits:64] map[Name:robust_list OffsetBits:41472 SizeBits:64] map[Name:compat_robust_list OffsetBits:41536 SizeBits:64] map[Name:pi_state_list OffsetBits:41600 SizeBits:128] map[Name:pi_state_cache OffsetBits:41728 SizeBits:64] map[Name:futex_exit_mutex OffsetBits:41792 SizeBits:1024] map[Name:futex_state OffsetBits:42816 SizeBits:32] map[Name:perf_recursion OffsetBits:42848 SizeBits:32] map[Name:perf_event_ctxp OffsetBits:42880 SizeBits:64] map[Name:perf_event_mutex OffsetBits:42944 SizeBits:1024] map[Name:perf_event_list OffsetBits:43968 SizeBits:128] map[Name:perf_ctx_data OffsetBits:44096 SizeBits:64] map[Name:preempt_disable_ip OffsetBits:44160 SizeBits:64] map[Name:mempolicy OffsetBits:44224 SizeBits:64] map[Name:il_prev OffsetBits:44288 SizeBits:16] map[Name:il_weight OffsetBits:44304 SizeBits:8] map[Name:pref_node_fork OffsetBits:44320 SizeBits:16] map[Name:rseq OffsetBits:44352 SizeBits:256] map[Name:mm_cid OffsetBits:44608 SizeBits:192] map[Name:tlb_ubc OffsetBits:44800 SizeBits:192] map[Name:splice_pipe OffsetBits:44992 SizeBits:64] map[Name:task_frag OffsetBits:45056 SizeBits:128] map[Name:delays OffsetBits:45184 SizeBits:64] map[Name:make_it_fail OffsetBits:45248 SizeBits:32] map[Name:fail_nth OffsetBits:45280 SizeBits:32] map[Name:nr_dirtied OffsetBits:45312 SizeBits:32] map[Name:nr_dirtied_pause OffsetBits:45344 SizeBits:32] map[Name:dirty_paused_when OffsetBits:45376 SizeBits:64] map[Name:timer_slack_ns OffsetBits:45440 SizeBits:64] map[Name:default_timer_slack_ns OffsetBits:45504 SizeBits:64] map[Name:kasan_depth OffsetBits:45568 SizeBits:32] map[Name:trace_recursion OffsetBits:45632 SizeBits:64] map[Name:kcov_mode OffsetBits:45696 SizeBits:32] map[Name:kcov_size OffsetBits:45728 SizeBits:32] map[Name:kcov_area OffsetBits:45760 SizeBits:64] map[Name:kcov OffsetBits:45824 SizeBits:64] map[Name:kcov_handle OffsetBits:45888 SizeBits:64] map[Name:kcov_sequence OffsetBits:45952 SizeBits:32] map[Name:kcov_softirq OffsetBits:45984 SizeBits:32] map[Name:memcg_in_oom OffsetBits:46016 SizeBits:64] map[Name:memcg_nr_pages_over_high OffsetBits:46080 SizeBits:32] map[Name:active_memcg OffsetBits:46144 SizeBits:64] map[Name:objcg OffsetBits:46208 SizeBits:64] map[Name:throttle_disk OffsetBits:46272 SizeBits:64] map[Name:utask OffsetBits:46336 SizeBits:64] map[Name:sequential_io OffsetBits:46400 SizeBits:32] map[Name:sequential_io_avg OffsetBits:46432 SizeBits:32] map[Name:kmap_ctrl OffsetBits:46464 SizeBits:2176] map[Name:task_state_change OffsetBits:48640 SizeBits:64] map[Name:saved_state_change OffsetBits:48704 SizeBits:64] map[Name:rcu OffsetBits:48768 SizeBits:128] map[Name:rcu_users OffsetBits:48896 SizeBits:32] map[Name:pagefault_disabled OffsetBits:48928 SizeBits:32] map[Name:oom_reaper_list OffsetBits:48960 SizeBits:64] map[Name:oom_reaper_timer OffsetBits:49024 SizeBits:640] map[Name:stack_vm_area OffsetBits:49664 SizeBits:64] map[Name:stack_refcount OffsetBits:49728 SizeBits:32] map[Name:security OffsetBits:49792 SizeBits:64] map[Name:bpf_storage OffsetBits:49856 SizeBits:64] map[Name:bpf_ctx OffsetBits:49920 SizeBits:64] map[Name:bpf_net_context OffsetBits:49984 SizeBits:64] map[Name:mce_vaddr OffsetBits:50048 SizeBits:64] map[Name:mce_kflags OffsetBits:50112 SizeBits:64] map[Name:mce_addr OffsetBits:50176 SizeBits:64] map[Name:mce_ripv OffsetBits:50240 SizeBits:1] map[Name:mce_whole_page OffsetBits:50241 SizeBits:1] map[Name:__mce_reserved OffsetBits:50242 SizeBits:62] map[Name:mce_kill_me OffsetBits:50304 SizeBits:128] map[Name:mce_count OffsetBits:50432 SizeBits:32] map[Name:l1d_flush_kill OffsetBits:50496 SizeBits:128] map[Name:unwind_info OffsetBits:50624 SizeBits:320] map[Name:thread OffsetBits:50944 SizeBits:1472]]]
|
| 78/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 74392
output: 21
thoughts: 680
Thoughts: **Analyzing a Kernel Corruption**
Okay, let's break this down. First, I see that `pi_lock` is at an offset of 0xad8. Now, the fault address is `0x0000000700000af0`. My initial thought was that if `owner` was calculated as the fault address minus the offset, then `owner` would be `0x0000000700000018`. However, that value *isn't* what was expected. Let me double-check that fault address, just to be sure... `0x0000000700000af0`.
Okay, if `owner` *is* `0x0000000700000018`, then `&owner->pi_lock` calculates correctly as `0x0000000700000018 + 0xad8 = 0x0000000700000af0`. So the address looks right. Therefore, `owner` *is* `0x0000000700000018`!
Now, where did this `owner` come from? Ah, it was assigned using `rt_mutex_owner(lock)`. And `rt_mutex_owner` does a bitwise AND with `~RT_MUTEX_HAS_WAITERS`. `RT_MUTEX_HAS_WAITERS` is 1, so the original `lock->owner` value had to have been either `0x0000000700000018` or `0x0000000700000019` -- I need to keep that in mind.
Where did `lock` come from? Oh, `lock` is `mapping->i_mmap_rwsem`. So, if `lock->owner` is `0x0000000700000018`, this directly translates to `mapping->i_mmap_rwsem.owner` being `0x0000000700000018`.
Aha! This strongly suggests that `mapping` is, in fact, a *valid* kernel address. But the *contents* of `mapping->i_mmap_rwsem.owner` have been corrupted.
Therefore, since `mapping` is valid, so is `file->f_mapping` which means `file` *itself* must be a valid kernel address. The bug isn't in a user-space address being used in the wrong spot, but rather the corruption of a critical kernel data structure: `mapping->i_mmap_rwsem.owner`.
Wait a minute, `mapping->i_mmap_rwsem` is an `rw_semaphore`! And on a PREEMPT_RT kernel, those are implemented using `rt_mutex`! That's the connection I was missing. Let me go check the `struct rw_semaphore` implementation for PREEMPT_RT to understand what it looks like.
|
| 79/2 |
2026/05/23 11:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:rwbase OffsetBits:0 SizeBits:768] map[Name:dep_map OffsetBits:768 SizeBits:320]]]
|
| 80/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 75849
output: 22
thoughts: 11
Thoughts: Here's a summary of my thought process, keeping in mind my expert understanding:
**Analyzing the `struct rwbase_rt`**
Okay, time to dive into `struct rwbase_rt`. I need to understand its role and how it's being used. Based on my experience, this likely holds the runtime state or base information for something related to read/write operations. The name itself strongly suggests this. I'll need to immediately consider the data it contains. What fields are in there? Are there mutexes or spinlocks for synchronization? Are there reference counters or version numbers that indicate the current state of read/write access? How does this structure interact with the rest of the read-write infrastructure? Are there potential performance bottlenecks related to locking or contention, especially if it's heavily used in a multi-threaded environment? My first pass will be to identify the data elements inside the struct and then, based on the fields, develop a preliminary hypothesis about its purpose.
|
| 81/2 |
2026/05/23 11:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:readers OffsetBits:0 SizeBits:32] map[Name:rtmutex OffsetBits:64 SizeBits:704]]]
|
| 82/2 |
2026/05/23 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 76136
output: 23
thoughts: 29
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into the `rtmutex` Structure**
Right, so I'm looking at the `rtmutex` and immediately I'm zeroing in on a critical internal detail: its location, specifically, the `rtmutex` object's offset of 64 bits, or 8 bytes. That placement is always telling, and often indicates how it sits within a larger data structure or is aligned for performance reasons. This also suggests to me that it's probably *not* the first element, which I need to keep in mind.
To understand the context of what that offset *means*, I need to refresh my knowledge of the underlying structure. The next logical step is to check `struct rt_mutex_base`. It will inform me of the other elements in the object, their sizes, their relationships, and how the critical mutex attributes are represented. Knowing `rt_mutex_base` will allow me to immediately deduce the likely purpose of that initial offset of 8 bytes.
|
| 83/2 |
2026/05/23 11:10 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:wait_lock OffsetBits:0 SizeBits:512] map[Name:waiters OffsetBits:512 SizeBits:128] map[Name:owner OffsetBits:640 SizeBits:64]]]
|
| 84/2 |
2026/05/23 11:10 |
llm |
expert |
0m
Model:
Tokens:
input: 76487
output: 21
thoughts: 2153
Thoughts: **Analyzing a Kernel Crash During mmap on a Loop Device**
Okay, so I'm digging into this kernel crash, and the initial clue is an apparent corruption of the `rtmutex`'s owner field. Specifically, `mapping->i_mmap_rwsem.rwbase.rtmutex.owner` is set to `0x0000000700000018`, which is... strange. I start by calculating the offset of this `owner` field within the `mapping` structure β it's at 584 bytes from the base of `mapping`, which is the base of file's backing `i_mapping`.
The immediate red flag is that this value looks suspicious. It looks like a user-space address. My first thought is that the `mapping` itself might be a user-space address, in which case the calculation puts `mapping` at `0x00000007000008a8`. But, if that were the case, accesses within `raw_spin_lock` should have triggered a crash earlier β at the `raw_spin_lock(&lock->wait_lock)` call in `rt_mutex_slowlock`.
Now I'm looking for a way to get a user-space address into kernel memory and trying to figure out how `lock->wait_lock` became valid. I calculate the offset of `wait_lock`, which is at 8 bytes from `rtmutex` which in this case is `0x00000007000008a8 + 496 + 8 = 0x0000000700000aa0`. I expect the crash at the `wait_lock` location if it's a user-space address, and I calculate the same. But no, the crash is actually in `raw_spin_lock(&owner->pi_lock)`. That means the previous `raw_spin_lock` call succeeded on a user-space address!
So that's weird. If the initial load of `owner` was from kernel memory, why does it have the wrong value? A bit flip? A use-after-free situation? But the relevant structure is `file->f_mapping` which if it's a block device, should point to a valid inode...
Thinking about the `loop` device, it's possible that the block device gets freed. If the device is destroyed while `mmap` is active, it could explain a lot. But `file` is held open, so it can't be freed.
I then consider the "backing file" of the loop device. What if *that* is somehow involved, and maybe it's the `file` that is user-space? I check `loop_assign_backing_file`, and it sets masks on the backing file. But it doesn't change `bdev->bd_inode->i_mapping`, so that's not it.
Then I get it! What if `file` itself is a user-space address? Then `file->f_mapping` would be read from user-space, which could then point to `0x00000007000008a8`. That means `lock` is at `0x0000000700000aa0`. I'd expect KASAN to catch this at the `raw_spin_lock` call, because `0x0000000700000aa0` is a user-space address. But KASAN reported the bug at `0x0000000700000af0`! That is the lock which is used by `owner`. That is where it crashes!
Then I remember that `raw_spin_lock` does more than just read the lock itself: It calls `lock_acquire`, and that checks `lock->dep_map`. The crash is in `lock_acquire`, which means `lock->dep_map` is being accessed. If `lock` is `&owner->pi_lock`, then it's accessing `owner->pi_lock.dep_map`. Ah ha! The problem isn't the lock itself, but a structure *within* the lock. I need to examine the `raw_spinlock_t` structure. That is `owner->pi_lock` which is within the kernel. It seems `owner` has the corrupted value. It is not the lock itself, it is another member of the data structure. It looks like `owner` has been corrupted by the time it gets to the critical section!
|
| 85/2 |
2026/05/23 11:10 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:raw_lock OffsetBits:0 SizeBits:32] map[Name:magic OffsetBits:32 SizeBits:32] map[Name:owner_cpu OffsetBits:64 SizeBits:32] map[Name:owner OffsetBits:128 SizeBits:64] map[Name:dep_map OffsetBits:192 SizeBits:320]]]
|
| 86/2 |
2026/05/23 11:10 |
llm |
expert |
1m
Model:
Tokens:
input: 79788
output: 66
thoughts: 12234
Thoughts: **Analysis of a Kernel Crash in `task_blocks_on_rt_mutex`**
Okay, here's what I've figured out. We have a kernel crash inside `task_blocks_on_rt_mutex`. The fault address is `0x0000000700000af0`. This is where it gets interesting. I started by tracing the crash back to figure out which address was accessed, and how it was derived.
The code's trying to access `owner->pi_lock.dep_map` at `0x0000000700000af0`. Since the offset to `dep_map` is 24, and to `pi_lock` is 2776, it means the `owner` is likely at `0x0000000700000000`. So, `lock->owner` is `0x0000000700000000` or a variant that, after a bitwise AND, comes to that value. This is a crucial clue!
Now, this `0x0000000700000000` is a *very* specific value. It's not a typical kernel address. My first thought was this might be related to user-space, but the KASAN report is critical: the error is a general protection fault due to a non-canonical address, which means KASAN is trying to access the shadow memory for a user-space address. However, given that the fault is happening within kernel code, and KASAN is triggered, it means that the base address is a kernel one. Therefore, the crash is not because of a direct access.
The key observation is: if the address accessed were actually a valid user-space address, KASAN would've reported the fault at a different, calculated shadow address. It did not, meaning the base address, even if partially user-space-like, triggered a fault because it was a **kernel address**, which means the problem is that it is a **corrupted pointer**.
So, that address is a pointer, but something has corrupted it. This means we're looking at a memory corruption issue, likely a use-after-free or an out-of-bounds write. The crash happened inside `rwbase_write_lock`, which uses an `rt_mutex`. Looking at the trace, the lock `&owner->pi_lock` is accessed which means a valid pointer is accessed, though the object the pointer points to is corrupt.
The `owner` is derived from `lock->owner`, a pointer that the code reads. The critical function is `rt_mutex_owner()`, which effectively performs a bitwise operation (`READ_ONCE(lock->owner) & ~RT_MUTEX_HAS_WAITERS`). It looks like the value has been corrupted on the write. The value of `owner` is either `0x0000000700000000` or `0x0000000700000001` (if the bitwise AND is not set). However, what's crucial is that it is a *very* specific address.
The `lock` object itself comes from `mapping->i_mmap_rwsem.rwbase.rtmutex`. It means that `mapping` is at the beginning, which is the key variable here. `mapping` is set to `file->f_mapping` which comes from `vma->vm_file`. This is the crucial relationship that matters.
Now the question is: how could `lock->owner` become this corrupted value? We know the `mapping` value, and thus `lock` address, is valid. So it must be corrupted from the pointer `lock->owner`. The crash is at the use of a corrupted `lock->owner`. If the lock has a corrupted `owner`, this will lead to a crash.
My first thought was a UAF on the `address_space` structure (`mapping`). But, since it crashes inside `rt_mutex_slowlock`, this seems less likely since the spinlock is taken inside `rwbase_write_lock` before the call is made. So that path is okay.
A key clue from the log is the "loop1: detected capacity change". This suggests a loop device is involved. In fact, `file` could be a file backed by a block device (e.g., a loop device). It is possible, but not probable. What if syzkaller is creating and removing backing files while memory is being written?
Since `vma->vm_file` is a file object, that implies that the backing
|
| 87/2 |
2026/05/23 11:12 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 88/2 |
2026/05/23 11:12 |
llm |
expert |
0m
Model:
Tokens:
input: 93176
output: 852
thoughts: 260
Thoughts: **My Analysis Complete: A Concerning Memory Corruption**
Alright, the analysis is done, and it's time to put together a concise summary. My findings point towards a nasty memory corruption issue, and it's looking like it could be quite serious.
Essentially, I've tracked the crash to a corrupted `lock->owner` field within `mapping->i_mmap_rwsem`. This value, bizarrely, contains a user-space address - `0x0000000700000000` or `0x0000000700000001`. The problem arises when `task_blocks_on_rt_mutex` attempts to interact with the owner's `pi_lock`, specifically calculating the address of `owner->pi_lock.dep_map`, which ends up being a user-space address: `0x0000000700000af0`. The kernel's KASAN then rightly flags this as an illegal access since it's attempting to read a non-canonical shadow address, triggering a GPF.
This is a classic symptom of memory corruption. It's almost certainly a Use-After-Free (UAF) or Out-Of-Bounds (OOB) write, somewhere within either the `struct address_space` or, crucially, the `struct file` structure that's pointing to it. I'm seeing the memory integrity compromised within the file mapping itself, which is never a good sign.
The scary part? This vulnerability seems to be triggered by `mmap` and related system calls. This means it's accessible to unprivileged users, which makes this a prime candidate for privilege escalation. We need to prioritize this and look for any exploitable write primitive, now.
|
| 89/1 |
2026/05/23 11:12 |
action |
format-explanation |
0m
Results: map[Explanation:Based on the crash report and source code analysis, here is the assessment of
the bug:
**Root Cause Analysis:**
The crash occurs in `kasan_byte_accessible` when the kernel tries to acquire a
raw spinlock in `task_blocks_on_rt_mutex`.
Tracing the stack and the faulting address (`0x0000000700000af0`), we can
determine the exact sequence of events:
1. A thread calls `mmap` on a file (likely a block device like `/dev/loop1`),
which eventually calls `vma_link_file`.
2. `vma_link_file` attempts to write-lock the file's mapping semaphore:
`i_mmap_lock_write(mapping)`.
3. On `PREEMPT_RT` kernels, `rw_semaphore` is implemented using `rt_mutex`. The
lock is contended, so the thread enters the slow path (`rt_mutex_slowlock` ->
`task_blocks_on_rt_mutex`).
4. Inside `task_blocks_on_rt_mutex`, the kernel reads the current owner of the
lock (`lock->owner`) to perform priority inheritance: `owner =
rt_mutex_owner(lock);`.
5. It then attempts to lock the owner's `pi_lock`:
`raw_spin_lock(&owner->pi_lock);`.
6. The `raw_spin_lock` implementation (with lockdep enabled) accesses
`owner->pi_lock.dep_map`.
The faulting address is `0x0000000700000af0`. In `struct task_struct`, the
`pi_lock` is located at offset `2776` (`0xad8`), and its `dep_map` is at offset
`24` (`0x18`) within the spinlock.
`0xad8 + 0x18 = 0xaf0`.
This perfectly aligns with the faulting address, meaning the `owner` pointer
read from the `rt_mutex` was exactly `0x0000000700000000`!
Because `0x0000000700000000` is a user-space address, KASAN attempts to validate
it. However, KASAN shadow memory only covers kernel-space addresses. The
calculated shadow address for this user-space pointer is `0xdffffc00e000015e`,
which is a non-canonical address, resulting in the observed General Protection
Fault (GPF).
**Security Impact:**
The fact that `mapping->i_mmap_rwsem.rwbase.rtmutex.owner` contains a
controlled/garbage value (`0x0000000700000000` or `0x0000000700000001`) while
the `mapping` pointer itself is a valid kernel address strongly indicates a
**Use-After-Free (UAF)** or **Out-Of-Bounds (OOB) write** memory corruption. The
`struct address_space` (or the `struct file` pointing to it) was likely freed
and reallocated with user-controlled data before the `mmap` path accessed it.
- **Exploitable:** Yes. Memory corruptions involving core kernel structures like
`struct file` or `struct address_space` are highly exploitable and can lead to
local privilege escalation (LPE).
- **Denial of Service:** Yes. Triggering the bug causes a kernel panic/GPF.
- **Accessible From Unprivileged Processes / User Namespaces:** Yes. The bug is
triggered via standard `mmap` operations and potentially loop device
interactions, which can be reached by unprivileged users (or within user
namespaces where they have the necessary capabilities to configure loop
devices).]
|