In the Linux kernel, the following vulnerability has been resolved:
9p: skip nlink update in cacheless mode to fix WARN_ON
v9fs_dec_count() unconditionally calls drop_nlink() on regular files,
even when the inode's nlink is already zero. In cacheless mode the
client refetches inode metadata from the server (the source of truth)
on every operation, so by the time v9fs_remove() returns, the locally
cached nlink may already reflect the post-unlink value:
1. Client initiates unlink, server processes it and sets nlink to 0
2. Client refetches inode metadata (nlink=0) before unlink returns
3. Client's v9fs_remove() completes successfully
4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0
This race is easily triggered under heavy unlink workloads, such as
stress-ng's unlink stressor, producing the following warning:
WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8
Call trace:
drop_nlink+0x4c/0xc8
v9fs_remove+0x1e0/0x250 [9p]
v9fs_vfs_unlink+0x20/0x38 [9p]
vfs_unlink+0x13c/0x258
...
In cacheless mode the server is authoritative and the inode is on its
way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()
entirely when neither CACHE_META nor CACHE_LOOSE is set, which both
avoids the warning and removes a class of nlink races (two concurrent
unlinkers observing nlink > 0 and both calling drop_nlink()) that an
nlink == 0 guard alone would only narrow rather than close.
9p: skip nlink update in cacheless mode to fix WARN_ON
v9fs_dec_count() unconditionally calls drop_nlink() on regular files,
even when the inode's nlink is already zero. In cacheless mode the
client refetches inode metadata from the server (the source of truth)
on every operation, so by the time v9fs_remove() returns, the locally
cached nlink may already reflect the post-unlink value:
1. Client initiates unlink, server processes it and sets nlink to 0
2. Client refetches inode metadata (nlink=0) before unlink returns
3. Client's v9fs_remove() completes successfully
4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0
This race is easily triggered under heavy unlink workloads, such as
stress-ng's unlink stressor, producing the following warning:
WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8
Call trace:
drop_nlink+0x4c/0xc8
v9fs_remove+0x1e0/0x250 [9p]
v9fs_vfs_unlink+0x20/0x38 [9p]
vfs_unlink+0x13c/0x258
...
In cacheless mode the server is authoritative and the inode is on its
way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()
entirely when neither CACHE_META nor CACHE_LOOSE is set, which both
avoids the warning and removes a class of nlink races (two concurrent
unlinkers observing nlink > 0 and both calling drop_nlink()) that an
nlink == 0 guard alone would only narrow rather than close.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
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Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Sat, 15 Aug 2026 06:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: 9p: skip nlink update in cacheless mode to fix WARN_ON v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value: 1. Client initiates unlink, server processes it and sets nlink to 0 2. Client refetches inode metadata (nlink=0) before unlink returns 3. Client's v9fs_remove() completes successfully 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0 This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning: WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ... In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close. | |
| Title | 9p: skip nlink update in cacheless mode to fix WARN_ON | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-08-15T05:53:36.332Z
Reserved: 2026-08-09T03:40:39.910Z
Link: CVE-2026-72170
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-15T06:21:35.100
Modified: 2026-08-15T06:21:35.100
Link: CVE-2026-72170
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.