CVE-2026-92503
UnknownSummary
A fix was applied in the Linux kernel for an ABBA deadlock in ext4_xattr_inode_cache_find() triggered by concurrent extended attribute (xattr) workloads using the ea_inode mount option. The deadlock occurred between a transaction holding a reference to an mbcache entry and the eviction thread evicting the same EA inode. The fix introduces a new EXT4_IGET_NOWAIT flag that performs a non-blocking inode lookup and returns -ENOENT instead of waiting for eviction or creation to complete.
Risk Assessment
The deadlock can cause processes or the entire system to hang on ext4 volumes using the ea_inode option, posing a denial-of-service (availability) risk. It is triggered under concurrent extended attribute workloads.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-92503. Until patched, consider avoiding the ea_inode mount option on ext4 volumes subject to concurrent xattr operations.
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Original NVD description (English source)
In 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS