9p: skip nlink update in cacheless mode to fix WARN_ON
Summary
| CVE | CVE-2026-72170 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-08-15 06:21:35 UTC |
| Updated | 2026-08-15 06:21:35 UTC |
| 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. |
Risk And Classification
EPSS: 0.002090000 probability, percentile 0.113280000 (date 2026-08-15)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected ac89b2ef9b55924bcf922251f043ba73a32d05bb a5a682b016ef5b5384e28f6d652d47a8f8e73d37 git | Not specified |
| CNA | Linux | Linux | affected ac89b2ef9b55924bcf922251f043ba73a32d05bb de79c3f3643841b8659a71958df7cf2a66bfd409 git | Not specified |
| CNA | Linux | Linux | affected ac89b2ef9b55924bcf922251f043ba73a32d05bb 8d610017c992de705b304d3d727a6e3a86af6149 git | Not specified |
| CNA | Linux | Linux | affected ac89b2ef9b55924bcf922251f043ba73a32d05bb 8faccac11e1369adddf5d80f4a45af93f13b2e1a git | Not specified |
| CNA | Linux | Linux | affected ac89b2ef9b55924bcf922251f043ba73a32d05bb 574aa0b4799470ac814479f1138d19efe6262255 git | Not specified |
| CNA | Linux | Linux | affected 4.17 | Not specified |
| CNA | Linux | Linux | unaffected 4.17 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.6.145 6.6.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.97 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.40 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.1.5 7.1.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2-rc1 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.