CVE-2026-89691: nfsd: clear opcnt on compound arg release to prevent OOB read

CVE-2026-89691: nfsd: clear opcnt on compound arg release to prevent OOB read

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

nfsd: clear opcnt on compound arg release to prevent OOB read

nfsd4_release_compoundargs() resets args->ops to the inline iops[8]
array when the dynamically-allocated ops buffer is freed, but leaves
args->opcnt at its original value (which can be up to 200 for NFSv4.1+
compounds).

If rq_status_counter is stuck at an odd value (which can happen when
nfsd_dispatch() hits an error path after setting it odd), the RPC
status dumpit handler reads min(opcnt, 16) entries from args->ops[].
Since iops only has 8 elements and is the last field in struct
nfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory
and leaks it to userspace via netlink.

Zero opcnt unconditionally in nfsd4_release_compoundargs() so stale
compound metadata is never exposed through the status interface.

[ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ]

The Linux kernel CVE team has assigned CVE-2026-89691 to this issue.


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

	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 6.12.109 with commit 58bcdfb2b2e412088839ae740b1a95154dc0b8d0
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 6.18.50 with commit e879148867bd4c4cac42e063ffaffa187dddc6fe
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 7.2.4 with commit c1a4f7b1848f95302df598217e1c7a1410c2d0c5
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 7.3-rc1 with commit ae4c38555e81563b8dc5eae55ffd70f0ea97aa5a

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-2026-89691
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/nfs4xdr.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/58bcdfb2b2e412088839ae740b1a95154dc0b8d0
	https://git.kernel.org/stable/c/e879148867bd4c4cac42e063ffaffa187dddc6fe
	https://git.kernel.org/stable/c/c1a4f7b1848f95302df598217e1c7a1410c2d0c5
	https://git.kernel.org/stable/c/ae4c38555e81563b8dc5eae55ffd70f0ea97aa5a