# CVE-2024-26629: nfsd: fix RELEASE_LOCKOWNER

> A race condition in the Linux kernel NFS server can cause incorrect lock release errors, leading to client-server state desynchronization and potential denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Mar 2024
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2024-26629, DEBIAN-CVE-2024-26629, GHSA-x66g-5578-7px9, UBUNTU-CVE-2024-26629

## What is CVE-2024-26629?

CVE-2024-26629 is a medium-severity vulnerability in Linux kernel, published on 13 Mar 2024. 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:

nfsd: fix RELEASE_LOCKOWNER

The test on so_count in nfsd4_release_lockowner() is nonsense and
harmful.  Revert to using check_for_locks(), changing that to not sleep.

First: harmful.
As is documented in the kdoc comment for nfsd4_release_lockowner(), the
test on so_count can transiently return a false positive resulting in a
return of NFS4ERR_LOCKS_HELD when in fact no locks are held.  This is
clearly a protocol violation and with the Linux NFS client it can cause
incorrect behaviour.

If RELEASE_LOCKOWNER is sent while some other thread is still
processing a LOCK request which failed because, at the time that request
was received, the given owner held a conflicting lock, then the nfsd
thread processing that LOCK request can hold a reference (conflock) to
the lock owner that causes nfsd4_release_lockowner() to return an
incorrect error.

The Linux NFS client ignores that NFS4ERR_LOCKS_HELD error because it
never sends NFS4_RELEASE_LOCKOWNER without first releasing any locks, so
it knows that the error is impossible.  It assumes the lock owner was in
fact released so it feels free to use the same lock owner identifier in
some later locking request.

When it does reuse a lock owner identifier for which a previous RELEASE
failed, it will naturally use a lock_seqid of zero.  However the server,
which didn't release the lock owner, will expect a larger lock_seqid and
so will respond with NFS4ERR_BAD_SEQID.

So clearly it is harmful to allow a false positive, which testing
so_count allows.

The test is nonsense because ... well... it doesn't mean anything.

so_count is the sum of three different counts.
1/ the set of states listed on so_stateids
2/ the set of active vfs locks owned by any of those states
3/ various transient counts such as for conflicting locks.

When it is tested against '2' it is clear that one of these is the
transient reference obtained by find_lockowner_str_locked().  It is not
clear what the other one is expected to be.

In practice, the count is often 2 because there is precisely one state
on so_stateids.  If there were more, this would fail.

In my testing I see two circumstances when RELEASE_LOCKOWNER is called.
In one case, CLOSE is called before RELEASE_LOCKOWNER.  That results in
all the lock states being removed, and so the lockowner being discarded
(it is removed when there are no more references which usually happens
when the lock state is discarded).  When nfsd4_release_lockowner() finds
that the lock owner doesn't exist, it returns success.

The other case shows an so_count of '2' and precisely one state listed
in so_stateid.  It appears that the Linux client uses a separate lock
owner for each file resulting in one lock state per lock owner, so this
test on '2' is safe.  For another client it might not be safe.

So this patch changes check_for_locks() to use the (newish)
find_any_file_locked() so that it doesn't take a reference on the
nfs4_file and so never calls nfsd_file_put(), and so never sleeps.  With
this check is it safe to restore the use of check_for_locks() rather
than testing so_count against the mysterious '2'.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2024-26629?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-26629?

Apply the vendor's patch.

## Is CVE-2024-26629 being exploited?

There is no known exploitation of CVE-2024-26629 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-26629 and fix it if it is affected.

What it is: CVE-2024-26629 is a medium-severity vulnerability in Linux kernel, published on 13 Mar 2024. 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-2024-26629 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2024-26629/ (Markdown: https://insights.sbomify.com/CVE-2024-26629/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26629
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26629
- OSV: https://osv.dev/vulnerability/CVE-2024-26629

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26629/
Summaries are generated and may contain mistakes; the official description above is the record.