| 0/0 |
2026/05/25 17:01 |
flow |
assessment-security |
4m
Results: map[DenialOfService:false Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the security impact:
**Bug Mechanism:**
The bug is a data race reported by KCSAN between `generic_fillattr()` and
`__inode_add_bytes()`.
- `__inode_add_bytes()` updates `inode->i_blocks` while holding the
`inode->i_lock` spinlock.
- `generic_fillattr()` (called via `stat()` syscalls) reads `inode->i_blocks`
without holding any locks to populate the `kstat` structure returned to
user-space.
**Security Impact:**
This is a **benign data race** with **no security impact**.
The worst-case consequence of this race is that a concurrent `stat()` call might
read a torn or slightly outdated value of `i_blocks` (or other inode attributes
like `i_ctime`), resulting in a slightly inaccurate statistic being returned to
user-space. It does not lead to memory corruption, out-of-bounds accesses, or
any kernel instability.
In fact, a previous attempt to "fix" a similar data race in `shmem_getattr()` by
adding `inode_lock_shared()` (commit `d949d1d14fa2`) was explicitly reverted
(commit `d1aa0c04294e`) because it caused deadlocks over NFS. The revert commit
message explicitly notes: *"added just to silence a syzbot sanitizer splat:
added where there has never been any practical problem"*.
**Accessibility:**
- **Unprivileged Processes / User Namespaces:** Yes. Any unprivileged user can
trigger this data race by concurrently calling `stat()` and writing to a file
(e.g., a file in `tmpfs` / `shmem` as seen in the stack trace).
- **Remote / Peripheral / Filesystem / VM Triggers:** No. This is a local
concurrency issue in the VFS layer.
**Conclusion:**
The bug is not exploitable and does not cause a Denial of Service. It is a
harmless data race on a statistic field that is accessible to unprivileged local
users. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/25 17:01 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/05/25 17:01 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/1cef53159987078c7c3925003f63913e63da8b96]
|
| 3/1 |
2026/05/25 17:01 |
action |
kernel-builder |
0m
Results: map[KernelObj:/app/workdir/cache/build/4a2c7deb8a438f0153f4907b92589114e67ed632]
|
| 4/1 |
2026/05/25 17:01 |
action |
codesearch-prepare |
0m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/25 17:02 |
agent |
expert |
3m
Model:
Results: map[DenialOfService:false Exploitable:false 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:
==================================================================
BUG: KCSAN: data-race in generic_fillattr / inode_add_bytes
read-write to 0xffff88811c968910 of 8 bytes by task 18147 on cpu 1:
__inode_add_bytes fs/stat.c:907 [inline]
inode_add_bytes+0x47/0xe0 fs/stat.c:920
__dquot_alloc_space+0x180/0x8a0 fs/quota/dquot.c:1720
dquot_alloc_space_nodirty include/linux/quotaops.h:292 [inline]
dquot_alloc_block_nodirty include/linux/quotaops.h:319 [inline]
shmem_inode_acct_blocks+0x125/0x230 mm/shmem.c:236
shmem_alloc_and_add_folio mm/shmem.c:2005 [inline]
shmem_get_folio_gfp+0x5b2/0xd60 mm/shmem.c:2564
shmem_get_folio mm/shmem.c:2670 [inline]
shmem_write_begin+0xfc/0x1f0 mm/shmem.c:3303
generic_perform_write+0x183/0x490 mm/filemap.c:4325
shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3478
__kernel_write_iter+0x319/0x590 fs/read_write.c:621
dump_emit_page fs/coredump.c:1304 [inline]
dump_user_range+0xa73/0xd00 fs/coredump.c:1378
elf_core_dump+0x21a2/0x2330 fs/binfmt_elf.c:2109
coredump_write+0xacc/0xdd0 fs/coredump.c:1053
do_coredump fs/coredump.c:1132 [inline]
vfs_coredump+0x26dd/0x31e0 fs/coredump.c:1206
get_signal+0xd5c/0xf20 kernel/signal.c:3022
arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
exit_to_user_mode_loop kernel/entry/common.c:98 [inline]
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:244 [inline]
irqentry_exit_to_user_mode include/linux/irq-entry-common.h:315 [inline]
irqentry_exit+0x145/0x5d0 kernel/entry/common.c:162
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
read to 0xffff88811c968910 of 8 bytes by task 16825 on cpu 0:
generic_fillattr+0x27d/0x340 fs/stat.c:106
shmem_getattr+0x181/0x200 mm/shmem.c:1302
vfs_getattr_nosec+0x146/0x1e0 fs/stat.c:213
vfs_getattr+0x48/0x60 fs/stat.c:262
vfs_statx_path+0x28/0x140 fs/stat.c:299
vfs_statx+0xc4/0x170 fs/stat.c:356
vfs_fstatat+0x118/0x170 fs/stat.c:373
__do_sys_newfstatat fs/stat.c:538 [inline]
__se_sys_newfstatat+0x55/0x3e0 fs/stat.c:532
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:532
x64_sys_call+0x2c64/0x3020 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
value changed: 0x000000000001c4a8 -> 0x000000000001c4c0
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16825 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the security impact:
**Bug Mechanism:**
The bug is a data race reported by KCSAN between `generic_fillattr()` and `__inode_add_bytes()`.
- `__inode_add_bytes()` updates `inode->i_blocks` while holding the `inode->i_lock` spinlock.
- `generic_fillattr()` (called via `stat()` syscalls) reads `inode->i_blocks` without holding any locks to populate the `kstat` structure returned to user-space.
**Security Impact:**
This is a **benign data race** with **no security impact**.
The worst-case consequence of this race is that a concurrent `stat()` call might read a torn or slightly outdated value of `i_blocks` (or other inode attributes like `i_ctime`), resulting in a slightly inaccurate statistic being returned to user-space. It does not lead to memory corruption, out-of-bounds accesses, or any kernel instability.
In fact, a previous attempt to "fix" a similar data race in `shmem_getattr()` by adding `inode_lock_shared()` (commit `d949d1d14fa2`) was explicitly reverted (commit `d1aa0c04294e`) because it caused deadlocks over NFS. The revert commit message explicitly notes: *"added just to silence a syzbot sanitizer splat: added where there has never been any practical problem"*.
**Accessibility:**
- **Unprivileged Processes / User Namespaces:** Yes. Any unprivileged user can trigger this data race by concurrently calling `stat()` and writing to a file (e.g., a file in `tmpfs` / `shmem` as seen in the stack trace).
- **Remote / Peripheral / Filesystem / VM Triggers:** No. This is a local concurrency issue in the VFS layer.
**Conclusion:**
The bug is not exploitable and does not cause a Denial of Service. It is a harmless data race on a statistic field that is accessible to unprivileged local users.
|
| 6/2 |
2026/05/25 17:02 |
llm |
expert |
0m
Model:
Tokens:
input: 6783
output: 117
thoughts: 137
Thoughts: **Analyzing a KCSAN Data-Race Report**
Okay, so I've got a KCSAN data-race report pointing to a potential issue between `generic_fillattr` in `fs/stat.c` and `inode_add_bytes` somewhere. The report indicates a read-write race condition, specifically targeting an 8-byte region at memory address `0xffff88811c968910`. The value's changed, which is the immediate concern, going from `0x000000000001c4a8` to `0x000000000001c4c0`.
Based on the size of the write and the context, I'm almost certain this is `inode->i_blocks`, which makes sense given both functions' involvement with file metadata, particularly the size and allocation. Now it's time to dig into the code itself. I'm going to jump into `fs/stat.c` and carefully examine the `generic_fillattr` function and `inode_add_bytes`, looking closely at how they access and modify the `i_blocks` field. My aim is to isolate the critical path where this race is happening and understand the potential concurrency issues in the code. I have to think about locking, atomicity, and the overall data consistency.
|
| 7/2 |
2026/05/25 17:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/stat.c IncludeLines:true Name:generic_fillattr]
Results: map[SourceCode: 65: /**
66: * generic_fillattr - Fill in the basic attributes from the inode struct
67: * @idmap: idmap of the mount the inode was found from
68: * @request_mask: statx request_mask
69: * @inode: Inode to use as the source
70: * @stat: Where to fill in the attributes
71: *
72: * Fill in the basic attributes in the kstat structure from data that's to be
73: * found on the VFS inode structure. This is the default if no getattr inode
74: * operation is supplied.
75: *
76: * If the inode has been found through an idmapped mount the idmap of
77: * the vfsmount must be passed through @idmap. This function will then
78: * take care to map the inode according to @idmap before filling in the
79: * uid and gid filds. On non-idmapped mounts or if permission checking is to be
80: * performed on the raw inode simply pass @nop_mnt_idmap.
81: */
82: void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask,
83: struct inode *inode, struct kstat *stat)
84: {
85: vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
86: vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
87:
88: stat->dev = inode->i_sb->s_dev;
89: stat->ino = inode->i_ino;
90: stat->mode = inode->i_mode;
91: stat->nlink = inode->i_nlink;
92: stat->uid = vfsuid_into_kuid(vfsuid);
93: stat->gid = vfsgid_into_kgid(vfsgid);
94: stat->rdev = inode->i_rdev;
95: stat->size = i_size_read(inode);
96: stat->atime = inode_get_atime(inode);
97:
98: if (is_mgtime(inode)) {
99: fill_mg_cmtime(stat, request_mask, inode);
100: } else {
101: stat->ctime = inode_get_ctime(inode);
102: stat->mtime = inode_get_mtime(inode);
103: }
104:
105: stat->blksize = i_blocksize(inode);
106: stat->blocks = inode->i_blocks;
107:
108: if ((request_mask & STATX_CHANGE_COOKIE) && IS_I_VERSION(inode)) {
109: stat->result_mask |= STATX_CHANGE_COOKIE;
110: stat->change_cookie = inode_query_iversion(inode);
111: }
112:
113: }
SourceFile:fs/stat.c]
|
| 8/2 |
2026/05/25 17:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/stat.c IncludeLines:true Name:__inode_add_bytes]
Results: map[SourceCode: 904: /* Caller is here responsible for sufficient locking (ie. inode->i_lock) */
905: void __inode_add_bytes(struct inode *inode, loff_t bytes)
906: {
907: inode->i_blocks += bytes >> 9;
908: bytes &= 511;
909: inode->i_bytes += bytes;
910: if (inode->i_bytes >= 512) {
911: inode->i_blocks++;
912: inode->i_bytes -= 512;
913: }
914: }
SourceFile:fs/stat.c]
|
| 9/2 |
2026/05/25 17:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/stat.c IncludeLines:true Name:inode_add_bytes]
Results: map[SourceCode: 917: void inode_add_bytes(struct inode *inode, loff_t bytes)
918: {
919: spin_lock(&inode->i_lock);
920: __inode_add_bytes(inode, bytes);
921: spin_unlock(&inode->i_lock);
922: }
SourceFile:fs/stat.c]
|
| 10/2 |
2026/05/25 17:02 |
llm |
expert |
0m
Model:
Tokens:
input: 8514
output: 46
thoughts: 411
Thoughts: **Benign Data Race in `inode->i_blocks`**
Okay, so I'm looking at this code and the race is pretty clear β it's all about `inode->i_blocks`. Specifically, in `generic_fillattr`, we're directly assigning `inode->i_blocks` to `stat->blocks`:
```c
stat->blocks = inode->i_blocks;
```
Meanwhile, `__inode_add_bytes`, which increments `i_blocks`, is called while holding `inode->i_lock`. That's fine from a consistency point of view.
```c
inode->i_blocks += bytes >> 9;
```
The problem is that `generic_fillattr` reads `inode->i_blocks` without holding the same lock. It's a textbook data race. Now, is it actually exploitable? No, not really. It's really just a torn read, or perhaps reading an intermediate value as the counter is being updated.
Since `i_blocks` is a 64-bit value, on 32-bit architectures this could be a genuine torn read. On 64-bit architectures, it's a single instruction read, so it's technically still a data race, but at most the value is transient.
It's just the value that gets returned to user-space via `stat()`, so the worst-case scenario is `stat()` reporting a slightly incorrect `st_blocks` value. Ultimately, it's a benign data race.
I should double-check for any other implications. The `stat->blocks` is a `u64`, and `inode->i_blocks` is `blkcnt_t` which can be `u64` or `unsigned long`.
From a security perspective, is there any real impact? Nope. The value is just a statistic.
And, it's easily accessible by unprivileged processes, as any process can call `stat()` on a file being written to by another process. Can it cause a Denial of Service? Nope, it's just a data race on a statistic, so no. Can it be exploited? No, again, it just reads a statistic so it can't be exploited.
Just need to check if there are any recent patches for this.
|
| 11/2 |
2026/05/25 17:02 |
tool |
git-log |
0m
Args: map[MessageRegexps:[data-race in generic_fillattr] SourcePath:fs/stat.c SymbolName:generic_fillattr]
Results:
|
| 12/2 |
2026/05/25 17:02 |
llm |
expert |
0m
Model:
Tokens:
input: 9478
output: 27
thoughts: 15
Thoughts: Here's my thought process, summarized as you requested:
**Investigating a Potential Data Race in `inode->i_blocks`**
Okay, time to dive in. My initial thought is to specifically target potential data races related to the `inode->i_blocks` field. This particular variable is a common source of contention in filesystem code, and experience tells me that race conditions often manifest here. I'll need to explore how it's accessed, modified, and protected across different threads or processes. I need to figure out where the read/write operations happen and whether they're properly synchronized. Is there a mutex protecting it? Are atomic operations involved? What about memory barriers? I'll probably start with a grep search across the kernel source, focusing on references to that field. I'll also likely look for any locking primitives that are used near it. My goal is to pinpoint the exact locations where this critical variable is touched and determine if any of those accesses could lead to inconsistencies or corruption under concurrent access. This is a pretty standard first step when hunting down this class of bugs.
|
| 13/2 |
2026/05/25 17:02 |
tool |
git-log |
0m
Args: map[MessageRegexps:[generic_fillattr i_blocks]]
Results: map[Output:c90b31eaf9e7 ksmbd: remove unnecessary generic_fillattr in smb2_open
f8f484d1b667 eCryptfs: Add getattr function
222096ae7f76 [XFS] stop updating inode->i_blocks
]
|
| 14/2 |
2026/05/25 17:03 |
llm |
expert |
0m
Model:
Tokens:
input: 9830
output: 27
thoughts: 23
Thoughts: Okay, here's my summary, presented as a stream of thought:
**Checking for Patches & Potential Race Conditions**
Right, let's get down to brass tacks. I need to quickly assess the current state of things. My primary focus right now is on that troublesome `generic_fillattr` function and the potential for data races lurking within. I need to determine if there's an existing patch that addresses any known issues related to either of these areas. Hopefully, someone's already done the hard work and provided a solid fix. I'll start by digging into the usual repositories and patch databases. If a patch *is* out there, I need to understand its scope and implications β does it truly resolve the problem, or does it introduce any new vulnerabilities or performance bottlenecks? Conversely, if there's *no* readily available patch, I'll need to start thinking critically about the underlying code and how to proceed with a more thorough investigation. This could involve static analysis, dynamic testing, and potentially, writing a custom reproducer. The goal is to determine if a data race exists and develop a plan to resolve any identified concurrency issues. Let's see what we can find.
|
| 15/2 |
2026/05/25 17:03 |
tool |
git-log |
0m
Args: map[MessageRegexps:[generic_fillattr data-race]]
Results: map[Output:d949d1d14fa2 mm: shmem: fix data-race in shmem_getattr()
]
|
| 16/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 10168
output: 26
thoughts: 17
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and presented as if it were my own internal monologue:
**Investigating a Hash Value**
Alright, let's dive in. I see `d949d1d14fa2`. Immediately, my mind starts racing. That's a hash value, likely an MD5, SHA-1, or SHA-256. The format looks familiar. The length suggests it could be a variety of things - definitely not immediately discernible from just the hex string. I need to figure out the context. I'm thinking: What system is this from? What data does it likely represent? Is this a file hash? A password hash? A transaction ID? A database key?
My initial approach is to mentally run through my usual checklist:
* **Hashing Algorithm:** I need to quickly identify the hashing algorithm used. A quick online lookup or a quick hashing tool can help me determine it immediately, using known techniques and tests.
* **Source Context:** Where did this hash originate? Knowing the source - say, a log file, a database entry, a code repository, etc. - drastically narrows the possible meanings. I need to mentally reconstruct the probable system that created this value.
* **Data Type:** What kind of data is this hash representing? Text, an executable, an image, some metadata? This impacts the possible next steps.
* **Potential Collisions:** Given the algorithm (once identified), I need to consider the collision probability. Is this a system where collisions are a major concern? How robust is the system in question?
* **Reversibility:** Is this potentially a reversible hash? I know some algorithms are cryptographically designed to be irreversible, or extremely difficult to reverse. I might know this already based on the hash itself.
* **Known Hashes:** I'll run this hash through my mental database of common, well-known hashes for various systems and libraries. I've encountered countless hashes over the years. This might immediately identify it or give me a starting point.
* **Lookup:** I could also cross-reference online hash databases, or internal tools if those are available, for known occurrences of this specific hash value.
In short, I'm thinking of this as a detective puzzle. The hash is the clue. Now, I need to methodically gather more information to understand its meaning and its significance.
|
| 17/2 |
2026/05/25 17:04 |
tool |
git-show |
0m
Args:
Results: map[Output:commit d949d1d14fa281ace388b1de978e8f2cd52875cf
Author: Jeongjun Park <aha310510@gmail.com>
Date: Mon Sep 9 21:35:58 2024 +0900
mm: shmem: fix data-race in shmem_getattr()
I got the following KCSAN report during syzbot testing:
==================================================================
BUG: KCSAN: data-race in generic_fillattr / inode_set_ctime_current
write to 0xffff888102eb3260 of 4 bytes by task 6565 on cpu 1:
inode_set_ctime_to_ts include/linux/fs.h:1638 [inline]
inode_set_ctime_current+0x169/0x1d0 fs/inode.c:2626
shmem_mknod+0x117/0x180 mm/shmem.c:3443
shmem_create+0x34/0x40 mm/shmem.c:3497
lookup_open fs/namei.c:3578 [inline]
open_last_lookups fs/namei.c:3647 [inline]
path_openat+0xdbc/0x1f00 fs/namei.c:3883
do_filp_open+0xf7/0x200 fs/namei.c:3913
do_sys_openat2+0xab/0x120 fs/open.c:1416
do_sys_open fs/open.c:1431 [inline]
__do_sys_openat fs/open.c:1447 [inline]
__se_sys_openat fs/open.c:1442 [inline]
__x64_sys_openat+0xf3/0x120 fs/open.c:1442
x64_sys_call+0x1025/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
read to 0xffff888102eb3260 of 4 bytes by task 3498 on cpu 0:
inode_get_ctime_nsec include/linux/fs.h:1623 [inline]
inode_get_ctime include/linux/fs.h:1629 [inline]
generic_fillattr+0x1dd/0x2f0 fs/stat.c:62
shmem_getattr+0x17b/0x200 mm/shmem.c:1157
vfs_getattr_nosec fs/stat.c:166 [inline]
vfs_getattr+0x19b/0x1e0 fs/stat.c:207
vfs_statx_path fs/stat.c:251 [inline]
vfs_statx+0x134/0x2f0 fs/stat.c:315
vfs_fstatat+0xec/0x110 fs/stat.c:341
__do_sys_newfstatat fs/stat.c:505 [inline]
__se_sys_newfstatat+0x58/0x260 fs/stat.c:499
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:499
x64_sys_call+0x141f/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
value changed: 0x2755ae53 -> 0x27ee44d3
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3498 Comm: udevd Not tainted 6.11.0-rc6-syzkaller-00326-gd1f2d51b711a-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
==================================================================
When calling generic_fillattr(), if you don't hold read lock, data-race
will occur in inode member variables, which can cause unexpected
behavior.
Since there is no special protection when shmem_getattr() calls
generic_fillattr(), data-race occurs by functions such as shmem_unlink()
or shmem_mknod(). This can cause unexpected results, so commenting it out
is not enough.
Therefore, when calling generic_fillattr() from shmem_getattr(), it is
appropriate to protect the inode using inode_lock_shared() and
inode_unlock_shared() to prevent data-race.
Link: https://lkml.kernel.org/r/20240909123558.70229-1-aha310510@gmail.com
Fixes: 44a30220bc0a ("shmem: recalculate file inode when fstat")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Reported-by: syzbot <syzkaller@googlegroup.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/shmem.c b/mm/shmem.c
index c5adb987b23c..4ba1d00fabda 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1166,7 +1166,9 @@ static int shmem_getattr(struct mnt_idmap *idmap,
stat->attributes_mask |= (STATX_ATTR_APPEND |
STATX_ATTR_IMMUTABLE |
STATX_ATTR_NODUMP);
+ inode_lock_shared(inode);
generic_fillattr(idmap, request_mask, inode, stat);
+ inode_unlock_shared(inode);
if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
stat->blksize = HPAGE_PMD_SIZE;
]
|
| 18/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 12575
output: 43
thoughts: 979
Thoughts: **Data Race Deep Dive: inode_add_bytes and shmem_getattr**
Okay, so I'm looking at this data race report. The initial patch, `d949d1d14fa2`, addressed a race in `shmem_getattr` by holding `inode_lock_shared(inode)`. The specific issue was a race on `inode->i_ctime`. But my current bug report seems to be a very similar problem, except it's hitting `inode->i_blocks` instead. Itβs the same basic pattern: a read-write race condition involving `generic_fillattr` and `inode_add_bytes`.
The stack traces confirm my suspicion. The write is clearly going through `__inode_add_bytes` (within the `shmem_inode_acct_blocks` context) and the read is happening within `generic_fillattr`, which `shmem_getattr` calls. So we have `shmem_getattr` potentially reading while `shmem_inode_acct_blocks` is updating the same data. Classic race.
The original patchβs solution was to wrap `generic_fillattr` with `inode_lock_shared(inode)` in `shmem_getattr`. Since we're dealing with the same functions but just on different inode fields, this looks highly relevant. But here's the key question: does the locking hierarchy hold up? We know that `inode_add_bytes` uses `inode->i_lock` (a spinlock) and the fix uses `inode->i_rwsem` (a read-write semaphore) through `inode_lock_shared`.
Crucially, are these locks the same? Is the `i_lock` spinlock and the `i_rwsem` semaphore compatible or complementary? I need to check how `inode_add_bytes` interacts with that `i_rwsem`. Let's look more closely at the call chain involving `shmem_file_write_iter` to see how it might be interacting with the inode locks.
|
| 19/2 |
2026/05/25 17:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/shmem.c IncludeLines:true Name:shmem_file_write_iter]
Results: map[SourceCode:3462: static ssize_t shmem_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
3463: {
3464: struct file *file = iocb->ki_filp;
3465: struct inode *inode = file->f_mapping->host;
3466: ssize_t ret;
3467:
3468: inode_lock(inode);
3469: ret = generic_write_checks(iocb, from);
3470: if (ret <= 0)
3471: goto unlock;
3472: ret = file_remove_privs(file);
3473: if (ret)
3474: goto unlock;
3475: ret = file_update_time(file);
3476: if (ret)
3477: goto unlock;
3478: ret = generic_perform_write(iocb, from);
3479: unlock:
3480: inode_unlock(inode);
3481: return ret;
3482: }
SourceFile:mm/shmem.c]
|
| 20/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 14365
output: 39
thoughts: 130
Thoughts: **Analyzing Potential Concurrency Issues in `shmem`**
Okay, so I'm digging into this concurrency bug, and I think I've spotted something potentially problematic. I see that the `shmem_file_write_iter` function is taking the `inode_lock(inode)`. Right, that translates to `down_write(&inode->i_rwsem)`. So, that gives me exclusive write access to that inode's resource.
Now, if `shmem_getattr` is grabbing `inode_lock_shared(inode)` β meaning, using `down_read(&inode->i_rwsem)` β then we have a potential serialization point. The read lock in `shmem_getattr` *should* be properly serialized with the write lock from `shmem_file_write_iter`. One prevents the other from occurring concurrently, making sure that there is no race condition. However, the report is indicating there's a problem, so I need to make absolutely sure.
Wait a second⦠the bug report mentions `shmem_getattr` at line 1302 in `mm/shmem.c`. Let's confirm that location in the current codebase and see exactly what's going on there. I need to verify that what *should* be happening is actually what *is* happening. Time to dig into the current tree.
|
| 21/2 |
2026/05/25 17:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/shmem.c IncludeLines:true Name:shmem_getattr]
Results: map[SourceCode:1283: static int shmem_getattr(struct mnt_idmap *idmap,
1284: const struct path *path, struct kstat *stat,
1285: u32 request_mask, unsigned int query_flags)
1286: {
1287: struct inode *inode = path->dentry->d_inode;
1288: struct shmem_inode_info *info = SHMEM_I(inode);
1289:
1290: if (info->alloced - info->swapped != inode->i_mapping->nrpages)
1291: shmem_recalc_inode(inode, 0, 0);
1292:
1293: if (info->fsflags & FS_APPEND_FL)
1294: stat->attributes |= STATX_ATTR_APPEND;
1295: if (info->fsflags & FS_IMMUTABLE_FL)
1296: stat->attributes |= STATX_ATTR_IMMUTABLE;
1297: if (info->fsflags & FS_NODUMP_FL)
1298: stat->attributes |= STATX_ATTR_NODUMP;
1299: stat->attributes_mask |= (STATX_ATTR_APPEND |
1300: STATX_ATTR_IMMUTABLE |
1301: STATX_ATTR_NODUMP);
1302: generic_fillattr(idmap, request_mask, inode, stat);
1303:
1304: if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
1305: stat->blksize = HPAGE_PMD_SIZE;
1306:
1307: if (request_mask & STATX_BTIME) {
1308: stat->result_mask |= STATX_BTIME;
1309: stat->btime.tv_sec = info->i_crtime.tv_sec;
1310: stat->btime.tv_nsec = info->i_crtime.tv_nsec;
1311: }
1312:
1313: return 0;
1314: }
SourceFile:mm/shmem.c]
|
| 22/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 15421
output: 24
thoughts: 65
Thoughts: **Investigating the Missing Lock in shmem_getattr**
Okay, so I'm taking a look at the current `shmem_getattr` function, and I'm not seeing the `inode_lock_shared(inode)` call. That's a bit odd; I'd expect it to be there for proper synchronization, especially considering the potential concurrent access to the inode's attributes. Now, let's see, wasn't there a patch addressing something similar recently? Ah, yes, I seem to recall a patch, `d949d1d14fa2`, that was applied to `mm/shmem.c`. I need to verify whether that patch, and specifically that particular synchronization fix, is actually present in the current tree. Time to go dig that up.
|
| 23/2 |
2026/05/25 17:04 |
tool |
grepper |
0m
Error:
Args: map[Expression:inode_lock_shared.*generic_fillattr]
Results:
|
| 24/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 15692
output: 26
thoughts: 47
Thoughts: **Investigating a Potentially Missing Commit**
Okay, hold on a second. I have a hunch that this particular commit, `d949d1d14fa2`, might have been either reverted at some point, or perhaps it was never actually applied to the current working tree I'm looking at. It's a bit odd, and my intuition is telling me to double-check. The best way to do that is to grab the latest log entry to see if the hash is up to date, so I need to check the single commit history with `git log -1 d949d1d14fa2`. This should confirm if it's present and what happened to it.
|
| 25/2 |
2026/05/25 17:04 |
tool |
git-show |
0m
Args:
Results: map[Output:commit d949d1d14fa281ace388b1de978e8f2cd52875cf
Author: Jeongjun Park <aha310510@gmail.com>
Date: Mon Sep 9 21:35:58 2024 +0900
mm: shmem: fix data-race in shmem_getattr()
I got the following KCSAN report during syzbot testing:
==================================================================
BUG: KCSAN: data-race in generic_fillattr / inode_set_ctime_current
write to 0xffff888102eb3260 of 4 bytes by task 6565 on cpu 1:
inode_set_ctime_to_ts include/linux/fs.h:1638 [inline]
inode_set_ctime_current+0x169/0x1d0 fs/inode.c:2626
shmem_mknod+0x117/0x180 mm/shmem.c:3443
shmem_create+0x34/0x40 mm/shmem.c:3497
lookup_open fs/namei.c:3578 [inline]
open_last_lookups fs/namei.c:3647 [inline]
path_openat+0xdbc/0x1f00 fs/namei.c:3883
do_filp_open+0xf7/0x200 fs/namei.c:3913
do_sys_openat2+0xab/0x120 fs/open.c:1416
do_sys_open fs/open.c:1431 [inline]
__do_sys_openat fs/open.c:1447 [inline]
__se_sys_openat fs/open.c:1442 [inline]
__x64_sys_openat+0xf3/0x120 fs/open.c:1442
x64_sys_call+0x1025/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
read to 0xffff888102eb3260 of 4 bytes by task 3498 on cpu 0:
inode_get_ctime_nsec include/linux/fs.h:1623 [inline]
inode_get_ctime include/linux/fs.h:1629 [inline]
generic_fillattr+0x1dd/0x2f0 fs/stat.c:62
shmem_getattr+0x17b/0x200 mm/shmem.c:1157
vfs_getattr_nosec fs/stat.c:166 [inline]
vfs_getattr+0x19b/0x1e0 fs/stat.c:207
vfs_statx_path fs/stat.c:251 [inline]
vfs_statx+0x134/0x2f0 fs/stat.c:315
vfs_fstatat+0xec/0x110 fs/stat.c:341
__do_sys_newfstatat fs/stat.c:505 [inline]
__se_sys_newfstatat+0x58/0x260 fs/stat.c:499
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:499
x64_sys_call+0x141f/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
value changed: 0x2755ae53 -> 0x27ee44d3
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3498 Comm: udevd Not tainted 6.11.0-rc6-syzkaller-00326-gd1f2d51b711a-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
==================================================================
When calling generic_fillattr(), if you don't hold read lock, data-race
will occur in inode member variables, which can cause unexpected
behavior.
Since there is no special protection when shmem_getattr() calls
generic_fillattr(), data-race occurs by functions such as shmem_unlink()
or shmem_mknod(). This can cause unexpected results, so commenting it out
is not enough.
Therefore, when calling generic_fillattr() from shmem_getattr(), it is
appropriate to protect the inode using inode_lock_shared() and
inode_unlock_shared() to prevent data-race.
Link: https://lkml.kernel.org/r/20240909123558.70229-1-aha310510@gmail.com
Fixes: 44a30220bc0a ("shmem: recalculate file inode when fstat")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Reported-by: syzbot <syzkaller@googlegroup.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/shmem.c b/mm/shmem.c
index c5adb987b23c..4ba1d00fabda 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1166,7 +1166,9 @@ static int shmem_getattr(struct mnt_idmap *idmap,
stat->attributes_mask |= (STATX_ATTR_APPEND |
STATX_ATTR_IMMUTABLE |
STATX_ATTR_NODUMP);
+ inode_lock_shared(inode);
generic_fillattr(idmap, request_mask, inode, stat);
+ inode_unlock_shared(inode);
if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
stat->blksize = HPAGE_PMD_SIZE;
]
|
| 26/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 17766
output: 39
thoughts: 54
Thoughts: Okay, here's my take on those thoughts, framed as my own:
**Investigating a Code Search Result**
Alright, the commit made it into the tree, that's good. But, hang on a second. I just ran a `codesearch-definition-source` query for `shmem_getattr` and it *didn't* turn up `inode_lock_shared`. That's strange, really strange. It should have. I'm going to have to dive back into `mm/shmem.c` and take another look, specifically around that function, and make absolutely sure I didn't miss something critical in the search logic, or perhaps an subtle refactoring of the locking scheme. It's time to get my hands dirty and cross-reference, again.
|
| 27/2 |
2026/05/25 17:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/shmem.c IncludeLines:true Name:shmem_getattr]
Results: map[SourceCode:1283: static int shmem_getattr(struct mnt_idmap *idmap,
1284: const struct path *path, struct kstat *stat,
1285: u32 request_mask, unsigned int query_flags)
1286: {
1287: struct inode *inode = path->dentry->d_inode;
1288: struct shmem_inode_info *info = SHMEM_I(inode);
1289:
1290: if (info->alloced - info->swapped != inode->i_mapping->nrpages)
1291: shmem_recalc_inode(inode, 0, 0);
1292:
1293: if (info->fsflags & FS_APPEND_FL)
1294: stat->attributes |= STATX_ATTR_APPEND;
1295: if (info->fsflags & FS_IMMUTABLE_FL)
1296: stat->attributes |= STATX_ATTR_IMMUTABLE;
1297: if (info->fsflags & FS_NODUMP_FL)
1298: stat->attributes |= STATX_ATTR_NODUMP;
1299: stat->attributes_mask |= (STATX_ATTR_APPEND |
1300: STATX_ATTR_IMMUTABLE |
1301: STATX_ATTR_NODUMP);
1302: generic_fillattr(idmap, request_mask, inode, stat);
1303:
1304: if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
1305: stat->blksize = HPAGE_PMD_SIZE;
1306:
1307: if (request_mask & STATX_BTIME) {
1308: stat->result_mask |= STATX_BTIME;
1309: stat->btime.tv_sec = info->i_crtime.tv_sec;
1310: stat->btime.tv_nsec = info->i_crtime.tv_nsec;
1311: }
1312:
1313: return 0;
1314: }
SourceFile:mm/shmem.c]
|
| 28/2 |
2026/05/25 17:04 |
llm |
expert |
0m
Model:
Tokens:
input: 18626
output: 35
thoughts: 32
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience, and delivered as a first-person summary:
**Digging into a Kernel Regression**
Alright, that `d949d1d14fa2` commit got reverted, huh? That's a red flag. Before jumping to conclusions, I need to understand *why*. My first instinct is to immediately check the history of `mm/shmem.c`, given the code context. Let's see what `git log mm/shmem.c` reveals β hopefully, it exposes the reasoning behind the reversion and any related discussion. Time to hunt down the root cause.
|
| 29/2 |
2026/05/25 17:04 |
tool |
git-log |
0m
Args: map[MessageRegexps:[Revert "mm: shmem: fix data-race in shmem_getattr()"]]
Results: map[Output:d1aa0c04294e mm: revert "mm: shmem: fix data-race in shmem_getattr()"
]
|
| 30/2 |
2026/05/25 17:05 |
llm |
expert |
0m
Model:
Tokens:
input: 18877
output: 26
thoughts: 8
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Analyzing the Revert Commit**
Alright, so the initial thought is clearly about examining a "revert commit." My immediate thought process goes into high gear. What kind of revert are we talking about? Was it a simple undo of the last commit, a targeted reversion of a specific range, or something more complex like a merge revert? The context is key here. I'm already mentally running through potential scenarios: conflict resolution issues, the risk of data loss or corrupted history, and the codebase's state before and after the change it's reverting. I'm also considering the potential reasons for the revert β was the initial change poorly implemented, did it introduce a bug, or was it simply the wrong approach altogether? The history and context of this commit, and its relation to its target are paramount. Understanding these things will make or break me. Now, let's see what we're dealing with.
|
| 31/2 |
2026/05/25 17:05 |
tool |
git-show |
0m
Args:
Results: map[Output:commit d1aa0c04294e29883d65eac6c2f72fe95cc7c049
Author: Andrew Morton <akpm@linux-foundation.org>
Date: Fri Nov 15 16:57:24 2024 -0800
mm: revert "mm: shmem: fix data-race in shmem_getattr()"
Revert d949d1d14fa2 ("mm: shmem: fix data-race in shmem_getattr()") as
suggested by Chuck [1]. It is causing deadlocks when accessing tmpfs over
NFS.
As Hugh commented, "added just to silence a syzbot sanitizer splat: added
where there has never been any practical problem".
Link: https://lkml.kernel.org/r/ZzdxKF39VEmXSSyN@tissot.1015granger.net [1]
Fixes: d949d1d14fa2 ("mm: shmem: fix data-race in shmem_getattr()")
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jeongjun Park <aha310510@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/shmem.c b/mm/shmem.c
index e87f5d6799a7..568bb290bdce 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1166,9 +1166,7 @@ static int shmem_getattr(struct mnt_idmap *idmap,
stat->attributes_mask |= (STATX_ATTR_APPEND |
STATX_ATTR_IMMUTABLE |
STATX_ATTR_NODUMP);
- inode_lock_shared(inode);
generic_fillattr(idmap, request_mask, inode, stat);
- inode_unlock_shared(inode);
if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
stat->blksize = HPAGE_PMD_SIZE;
]
|
| 32/2 |
2026/05/25 17:05 |
llm |
expert |
0m
Model:
Tokens:
input: 19745
output: 66
thoughts: 316
Thoughts: **My Assessment of the Reverted Patch and the Underlying Data Race**
Alright, let's break this down. So, the patch got reverted due to deadlocks, and Hugh Dickins' comment is pretty clear: it was added just to quiet a syzbot sanitizer complaint, addressing a problem that hasn't materialized into any *practical* issues. That strongly suggests this data race is indeed benign, and has absolutely no security implications.
Essentially, we're looking at a data race, likely on either `inode->i_blocks` or possibly `inode->i_ctime`, that manifests when `stat()` is called concurrently with file modifications. It makes sense, these are fields that could be updated during modification and then read in `stat()`.
Now, let's categorize this thing:
* **Exploitable?** No, definitely not. It's a benign data race affecting a statistical field. No chance.
* **Denial of Service?** Nope. Doesn't crash the kernel, no resource leaks. Harmless.
* **Accessible from Unprivileged Processes?** Yes. Any user-space process can call `stat()` and `write()` on a file. That's the nature of these system calls.
* **Accessible from User Namespaces?** Yes, again, due to the nature of system calls.
* **VM Guest Trigger?** No, this is a host kernel issue.
* **VM Host Trigger (in Confidential Computing)?** Still no.
* **Ethernet Network Trigger?** Nope.
* **Other Remote Trigger?** No, not unless someone can remotely cause a local file write race.
* **Peripheral Trigger?** No.
* **Malicious Filesystem Trigger?** No.
Hmm, let's look at the bug report itself. The crash report seems to identify a read-write to an 8-byte region (likely the pointer to the struct). The stack trace points to `__inode_add_bytes` and `generic_fillattr`. That helps.
I've got the data I need. Time to set the final results.
|
| 33/2 |
2026/05/25 17:05 |
tool |
set-results |
0m
Args: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:false Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 34/2 |
2026/05/25 17:05 |
llm |
expert |
0m
Model:
Tokens:
input: 20646
output: 461
thoughts: 237
Thoughts: **Final Response: KCSAN Data-Race Analysis**
Okay, the analysis is done, time to put together the final response. It looks like we have a KCSAN data-race report between `generic_fillattr` and `__inode_add_bytes`, specifically on the `inode->i_blocks` field. The core issue is that `__inode_add_bytes` modifies `inode->i_blocks` while properly holding `inode->i_lock`, but `generic_fillattr` reads that same value without any locking at all. Classic data race scenario.
I immediately recognized this as a known, and thankfully, benign issue. There was a previous attempt to address a similar data race in `shmem_getattr` by introducing `inode_lock_shared` (d949d1d14fa2), but it got reverted (d1aa0c04294e) because of deadlocks. The relevant documentation makes it clear that while technically a data race, it doesn't cause any real-world problems. The worst that can happen is a `stat()` call returning a slightly incorrect or potentially torn value for `st_blocks`.
No memory corruption, no denial of service, and definitely no security implications. Anybody can trigger this since any user can call `stat()` and `write()` on a file concurrently, so it's a completely unprivileged access path. Looks like we can safely classify this as a false positive, or at least a low-priority issue.
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2026/05/25 17:05 |
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0m
Results: map[Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the security impact:
**Bug Mechanism:**
The bug is a data race reported by KCSAN between `generic_fillattr()` and
`__inode_add_bytes()`.
- `__inode_add_bytes()` updates `inode->i_blocks` while holding the
`inode->i_lock` spinlock.
- `generic_fillattr()` (called via `stat()` syscalls) reads `inode->i_blocks`
without holding any locks to populate the `kstat` structure returned to
user-space.
**Security Impact:**
This is a **benign data race** with **no security impact**.
The worst-case consequence of this race is that a concurrent `stat()` call might
read a torn or slightly outdated value of `i_blocks` (or other inode attributes
like `i_ctime`), resulting in a slightly inaccurate statistic being returned to
user-space. It does not lead to memory corruption, out-of-bounds accesses, or
any kernel instability.
In fact, a previous attempt to "fix" a similar data race in `shmem_getattr()` by
adding `inode_lock_shared()` (commit `d949d1d14fa2`) was explicitly reverted
(commit `d1aa0c04294e`) because it caused deadlocks over NFS. The revert commit
message explicitly notes: *"added just to silence a syzbot sanitizer splat:
added where there has never been any practical problem"*.
**Accessibility:**
- **Unprivileged Processes / User Namespaces:** Yes. Any unprivileged user can
trigger this data race by concurrently calling `stat()` and writing to a file
(e.g., a file in `tmpfs` / `shmem` as seen in the stack trace).
- **Remote / Peripheral / Filesystem / VM Triggers:** No. This is a local
concurrency issue in the VFS layer.
**Conclusion:**
The bug is not exploitable and does not cause a Denial of Service. It is a
harmless data race on a statistic field that is accessible to unprivileged local
users.]
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