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.

...

Classification

CVE ID: CVE-2024-26629

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 12.38% (scored less or equal to compared to others)

EPSS Date: 2025-02-03 (when was this score calculated)

References

https://git.kernel.org/stable/c/99fb654d01dc3f08b5905c663ad6c89a9d83302f
https://git.kernel.org/stable/c/c6f8b3fcc62725e4129f2c0fd550d022d4a7685a
https://git.kernel.org/stable/c/e4cf8941664cae2f89f0189c29fe2ce8c6be0d03
https://git.kernel.org/stable/c/b7d2eee1f53899b53f069bba3a59a419fc3d331b
https://git.kernel.org/stable/c/8f5b860de87039b007e84a28a5eefc888154e098
https://git.kernel.org/stable/c/edcf9725150e42beeca42d085149f4c88fa97afd

Timeline