# CVE-2026-92503: ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find()

> A race condition in the Linux kernel ext4 filesystem causes an ABBA deadlock during concurrent extended attribute operations, leading to system denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102104, BELL-CVE-2026-92503, DEBIAN-CVE-2026-92503, GHSA-4ppx-vw73-jjc6, UBUNTU-CVE-2026-92503

## What is CVE-2026-92503?

CVE-2026-92503 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2026-92503?


## How do I fix CVE-2026-92503?

Apply the vendor's patch.

## Is CVE-2026-92503 being exploited?

There is no known exploitation of CVE-2026-92503 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-92503 and fix it if it is affected.

What it is: CVE-2026-92503 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-92503 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-92503/ (Markdown: https://insights.sbomify.com/CVE-2026-92503/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-92503
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-92503
- OSV: https://osv.dev/vulnerability/CVE-2026-92503

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-92503/
Summaries are generated and may contain mistakes; the official description above is the record.