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CVE-2026-72170

9p: skip nlink update in cacheless mode to fix WARN_ON

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.266, 5.15.217, 6.1.184, 6.6.145, 6.12.97, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in 6086469f7d469549bfd070348b717a6e43736200; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in ab257019cb72f467b55c95384d99c94e3908b928; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in 4ec4ebe40c82cb4c60756732f6593055d010c59c; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in a5a682b016ef5b5384e28f6d652d47a8f8e73d37; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in de79c3f3643841b8659a71958df7cf2a66bfd409; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in 8d610017c992de705b304d3d727a6e3a86af6149; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in 8faccac11e1369adddf5d80f4a45af93f13b2e1a; From ac89b2ef9b55924bcf922251f043ba73a32d05bb · fixed in 574aa0b4799470ac814479f1138d19efe6262255

  • Linux Linux

    4.17

  • KernelLinux

    From 4.17.0 · fixed in 5.10.266; From 5.11.0 · fixed in 5.15.217; From 5.16.0 · fixed in 6.1.184; From 6.2.0 · fixed in 6.6.145; From 6.7.0 · fixed in 6.12.97; From 6.13.0 · fixed in 6.18.40; From 6.19.0 · fixed in 7.1.5

References 8

git.kernel.org