From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-89711: NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check
Date: Fri, 11 Sep 2026 21:46:40 +0200 [thread overview]
Message-ID: <2026091158-CVE-2026-89711-221f@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check
The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in
fh_verify of directories") details the assumption that justified
adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is
invalid (in the case of NFS reexport).
When NFSD exports an NFS filesystem it is very possible for
nfsd_mode_check() to encounter a @dentry that doesn't have
i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and
NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()).
So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir
return on that branch must stay. It guards the subsequent
lookup_one_unlocked() -> __lookup_slow() path, which calls
inode->i_op->lookup() with no NULL check, so returning nfserr_notdir
is what keeps a client LOOKUP into such a @dentry from dereferencing
a NULL method pointer.
The Linux kernel CVE team has assigned CVE-2026-89711 to this issue.
Affected and fixed versions
===========================
Issue introduced in 4.8 with commit e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c and fixed in 6.12.109 with commit b55b4d880bb080fa10eb08ba21a5d8679b8102fe
Issue introduced in 4.8 with commit e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c and fixed in 6.18.50 with commit 7ef182a8fe9c12b0d936880b1e504840639aa009
Issue introduced in 4.8 with commit e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c and fixed in 7.2.4 with commit a275de3bac5635514ca830f2e46b5ff0e66b5c4c
Issue introduced in 4.8 with commit e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c and fixed in 7.3-rc1 with commit aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e
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-2026-89711
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/nfsfh.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/b55b4d880bb080fa10eb08ba21a5d8679b8102fe
https://git.kernel.org/stable/c/7ef182a8fe9c12b0d936880b1e504840639aa009
https://git.kernel.org/stable/c/a275de3bac5635514ca830f2e46b5ff0e66b5c4c
https://git.kernel.org/stable/c/aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e
reply other threads:[~2026-09-11 20:03 UTC|newest]
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