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.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
ac89b2ef9b55924bcf922251f043ba73a32d05bb to < 6086469f7d469549bfd070348b717a6e43736200affectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < ab257019cb72f467b55c95384d99c94e3908b928affectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < 4ec4ebe40c82cb4c60756732f6593055d010c59caffectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < a5a682b016ef5b5384e28f6d652d47a8f8e73d37affectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < de79c3f3643841b8659a71958df7cf2a66bfd409affectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < 8d610017c992de705b304d3d727a6e3a86af6149affectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < 8faccac11e1369adddf5d80f4a45af93f13b2e1aaffectedac89b2ef9b55924bcf922251f043ba73a32d05bb to < 574aa0b4799470ac814479f1138d19efe6262255affected
Linux Linux
Default version status: affected
4.17affected0 to < 4.17unaffected5.10.266 to ≤ 5.10.*unaffected5.15.217 to ≤ 5.15.*unaffected6.1.184 to ≤ 6.1.*unaffected6.6.145 to ≤ 6.6.*unaffected6.12.97 to ≤ 6.12.*unaffected6.18.40 to ≤ 6.18.*unaffected7.1.5 to ≤ 7.1.*unaffected7.2 to ≤ *unaffected
References
- https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200 ↗
- https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928 ↗
- https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c ↗
- https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37 ↗
- https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409 ↗
- https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149 ↗
- https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a ↗
- https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255 ↗