From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-89659: NFSD: Prevent client use-after-free during delegation revoke
Date: Fri, 11 Sep 2026 21:45:48 +0200 [thread overview]
Message-ID: <2026091146-CVE-2026-89659-32e5@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
NFSD: Prevent client use-after-free during delegation revoke
A delegation stateid holds only a bare pointer to its owning
nfs4_client and does not keep it alive. The client survives its
stateids only because __destroy_client() drains cl_delegations and
cl_revoked before free_client() runs.
nfs4_laundromat() breaks that invariant: it unhashes an
expired delegation from cl_delegations, drops deleg_lock, then
revoke_delegation() relinks it onto cl_revoked under cl_lock. In that
window the delegation is on neither list, so client_has_state() can
report no remaining state.
Every teardown path first requires cl_rpc_users to be zero, but
the laundromat holds no such reference. A client whose recalled
delegation has just timed out can therefore reach free_client()
while revoke_delegation() is still about to dereference cl_lock,
a use-after-free.
Pin the client with cl_rpc_users across the revoke so teardown blocks
until it completes, then reap the delegation from cl_revoked. A client
already expiring reaps its own, so skip it and leave the delegation on
del_recall_lru.
The Linux kernel CVE team has assigned CVE-2026-89659 to this issue.
Affected and fixed versions
===========================
Issue introduced in 3.10 with commit 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 and fixed in 6.18.51 with commit 3c0a53ee0b442348d8d2286d6960d3f07bb3a3d3
Issue introduced in 3.10 with commit 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 and fixed in 7.2.4 with commit 2a9d637c2a8fd8ac29ad9b29f28d122ef75c1a56
Issue introduced in 3.10 with commit 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 and fixed in 7.3-rc1 with commit 4683ca76b3b7e5808338491c6eb3c20e6b4894d5
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-2026-89659
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/netns.h
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/3c0a53ee0b442348d8d2286d6960d3f07bb3a3d3
https://git.kernel.org/stable/c/2a9d637c2a8fd8ac29ad9b29f28d122ef75c1a56
https://git.kernel.org/stable/c/4683ca76b3b7e5808338491c6eb3c20e6b4894d5
reply other threads:[~2026-09-11 20:01 UTC|newest]
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