ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-92503
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:17:52 UTC
Updated2026-09-17 17:17:52 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() Syzbot/stress-ng reported an ABBA deadlock in ext4 when exercising concurrent xattr workloads (using the ea_inode mount/format option). The deadlock occurs between the running transaction and the eviction thread: - Task 1 (stress-ng): Holds a reference to a shared mbcache_entry (ce) and calls ext4_xattr_inode_cache_find() -> ext4_iget() to retrieve the corresponding EA inode. Since the EA inode is currently being evicted, ext4_iget() blocks in __wait_on_freeing_inode() waiting for eviction to complete. - Task 2 (eviction thread): Currently evicting the same EA inode in ext4_evict_ea_inode(). It calls mb_cache_entry_wait_unused(oe) which blocks waiting for Task 1 to release the reference to the mbcache_entry. To break this deadlock, implement a new ext4_iget() configuration flag named EXT4_IGET_NOWAIT. When set, perform a non-blocking lookup of the inode via VFS's find_inode_nowait() API. If the inode is currently being evicted (marked with I_FREEING or I_WILL_FREE) or created (I_CREATING), or if it is not present in the VFS inode cache (cache miss), simply skip it (returning -ENOENT) rather than waiting for eviction/creation to complete, breaking the ABBA cycle. Since we return -ENOENT immediately on a cache miss, we never attempt to allocate a new inode or call iget_locked(), completely eliminating any TOCTOU race window. If the returned inode is I_NEW, wait for its initialization to clear via wait_on_new_inode(). If initialization fails and the inode is unhashed during wait_on_new_inode() waking up (e.g., due to an I/O read error in another thread), safely drop the reference and return -ENOENT. This unhashed check is executed unconditionally on all cache-hit pathways to properly handle concurrent initialization failures. Finally, standard validation checks (including is_bad_inode, EXT4_EA_INODE_FL, file_acl, and xattr flags) are executed as normal inside check_igot_inode() to fully guarantee VFS-layer safety. In ext4_xattr_inode_cache_find(), invoke ext4_iget() with the new EXT4_IGET_NOWAIT flag to perform the non-blocking cache search.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 0a46ef234756dca04623b7591e8ebb3440622f0b 7720fddd1fe344d14be258a2028f74ebf1569511 git Not specified
CNA Linux Linux affected 0a46ef234756dca04623b7591e8ebb3440622f0b 03438084a7b8621fb5c762dd3d04cff5f2630fb2 git Not specified
CNA Linux Linux affected 0752e7fb549d90c33b4d4186f11cfd25a556d1dd git Not specified
CNA Linux Linux affected 737fb7853acd5bc8984f6f42e4bfba3334be8ae1 git Not specified
CNA Linux Linux affected 111103907234bffd0a34fba070ad9367de058752 git Not specified
CNA Linux Linux affected 6.1.107 6.2 semver Not specified
CNA Linux Linux affected 6.6.47 6.7 semver Not specified
CNA Linux Linux affected 6.9.7 6.10 semver Not specified
CNA Linux Linux affected 6.10 Not specified
CNA Linux Linux unaffected 6.10 semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/7720fddd1fe344d14be258a2028f74ebf1569511 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/03438084a7b8621fb5c762dd3d04cff5f2630fb2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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