Cloudanix VulnDB

CVE-2026-92503

None

CVSS

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EPSS

0.2%

Published

Sep 17, 2026

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A flaw in the Linux ext4 filesystem could cause the operating system to freeze when multiple programs try to handle file attributes at the same time, requiring a reboot to recover.

Exploitation
Local Privilege
Attacker needs
Local User
Complexity
Moderate
Impact
Denial Of Service
Component
OS kernel
Class
Race Condition
Remediation
Patch
Effort
Medium
Patch risk
Low

What it actually does

ABBA deadlock between a transaction holding an mbcache_entry reference and calling ext4_xattr_inode_cache_find() which blocks in ext4_iget() on an inode being evicted, and the eviction thread waiting on mb_cache_entry_wait_unused() for the reference to be released.

Why it matters to the business

Systems running Linux kernels with the ea_inode ext4 mount option under concurrent extended-attribute workloads may experience kernel-level hangs that require reboot, leading to temporary loss of service and potential data inconsistency on affected filesystems; risk remains low given stable low exploit probability and no observed in-the-wild use.

How an attack unfolds

An attacker with local access triggers concurrent xattr operations on an ext4 filesystem mounted with ea_inode, causing one task to hold a cache reference while another evicts the inode, resulting in mutual waiting that deadlocks the filesystem; the race is difficult to win reliably and requires specific workload conditions not commonly present in normal operation.

How to fix it

Upgrade to a Linux kernel containing the EXT4_IGET_NOWAIT change that replaces blocking ext4_iget calls in ext4_xattr_inode_cache_find with non-blocking find_inode_nowait lookups returning -ENOENT on I_FREEING/I_WILL_FREE/I_CREATING states.

How to confirm the fix worked

Confirm the kernel source contains the EXT4_IGET_NOWAIT flag definition and its use inside ext4_xattr_inode_cache_find, then boot the updated kernel and run concurrent xattr stress tests to verify absence of deadlock.

Typical attack path

  1. Mount ext4 with ea_inode option
  2. Run parallel stress-ng or similar xattr workloads
  3. Trigger eviction of an EA inode while another task holds mbcache reference
  4. ext4_iget blocks in __wait_on_freeing_inode while eviction blocks in mb_cache_entry_wait_unused

How to detect it

Inspect kernel logs for hung-task or deadlock warnings mentioning ext4_xattr_inode_cache_find or ext4_evict_ea_inode; correlate with processes performing heavy xattr operations on ea_inode-enabled filesystems.

What your security team should do

  • Prioritize kernel updates on any ext4 deployments using the ea_inode mount option
  • Monitor for kernel oops or hung-task messages related to ext4_evict_ea_inode
  • Apply the fix even on systems without the mount option as a defense-in-depth measure
  • Re-test xattr-heavy workloads after patching to confirm deadlock resolution

The record

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.

Affected packages

Ecosystem Package Introduced Fixed