From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-89682: nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net
Date: Fri, 11 Sep 2026 21:46:11 +0200 [thread overview]
Message-ID: <2026091151-CVE-2026-89682-1079@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net
nfsd_file_dispose_list_delayed() defers fput() to nfsd service threads
via a per-net freeme queue, preventing the shrinker and GC worker from
bearing the cost of closing files (see ffb402596147). However, the
queue lives in a separately-allocated struct nfsd_fcache_disposal that
is freed by nfsd_free_fcache_disposal_net() during per-net teardown.
The global shrinker, laundrette, and fsnotify callbacks can still be
inside nfsd_file_dispose_list_delayed() dereferencing that pointer,
causing a use-after-free.
Inline the spinlock and freeme list directly into struct nfsd_net (as
fcache_dispose_lock and fcache_dispose_list), eliminating the separately
allocated struct nfsd_fcache_disposal entirely. These fields now have
the same lifetime as the net namespace itself, so there is no dangling
pointer to chase.
nfsd_file_cache_start_net() now just initializes the inline fields and
cannot fail due to allocation. nfsd_file_cache_shutdown_net() drains
the inline list directly instead of freeing a separate struct. The
alloc/free helpers are removed.
The Linux kernel CVE team has assigned CVE-2026-89682 to this issue.
Affected and fixed versions
===========================
Issue introduced in 5.17 with commit 1463b38e7cf34d4cc60f41daff459ad807b2e408 and fixed in 6.18.51 with commit ba0ee9e04b7a0356c28d5a2fe445db675d24e572
Issue introduced in 5.17 with commit 1463b38e7cf34d4cc60f41daff459ad807b2e408 and fixed in 7.2.4 with commit cadc9036d5a8209f89e7026ddba7cfb1c716b03c
Issue introduced in 5.17 with commit 1463b38e7cf34d4cc60f41daff459ad807b2e408 and fixed in 7.3-rc1 with commit bbf13732f74351d21c5e0e8dd9bd8e1c48dc35d4
Issue introduced in 5.10.220 with commit e8f923e1e9fcc0832a12c8a2461792e5a9544c03
Issue introduced in 5.15.154 with commit 3bc94fb44f10ef852723e1aeaac6794c5ab16aec
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-2026-89682
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/filecache.c
fs/nfsd/netns.h
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/ba0ee9e04b7a0356c28d5a2fe445db675d24e572
https://git.kernel.org/stable/c/cadc9036d5a8209f89e7026ddba7cfb1c716b03c
https://git.kernel.org/stable/c/bbf13732f74351d21c5e0e8dd9bd8e1c48dc35d4
reply other threads:[~2026-09-11 20:02 UTC|newest]
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