Subject: CVE-2024-50043: nfsd: fix possible badness in FREE_STATEID

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix possible badness in FREE_STATEID

When multiple FREE_STATEIDs are sent for the same delegation stateid,
it can lead to a possible either use-after-free or counter refcount
underflow errors.

In nfsd4_free_stateid() under the client lock we find a delegation
stateid, however the code drops the lock before calling nfs4_put_stid(),
that allows another FREE_STATE to find the stateid again. The first one
will proceed to then free the stateid which leads to either
use-after-free or decrementing already zeroed counter.

The Linux kernel CVE team has assigned CVE-2024-50043 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.9 with commit 3f29cc82a84c and fixed in 6.11.4 with commit 7ca9e472ce5c
	Issue introduced in 6.9 with commit 3f29cc82a84c and fixed in 6.12-rc3 with commit c88c150a467f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-50043
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/nfsd/nfs4state.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/7ca9e472ce5c67daa3188a348ece8c02a0765039
	https://git.kernel.org/stable/c/c88c150a467fcb670a1608e2272beeee3e86df6e