linux-cve-announce - CVE-2026-23189: ceph: fix NULL pointer dereference in ceph_mds_auth

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Message-ID: <2026021432-CVE-2026-23189-3d9f@gregkh>
Date: Sat, 14 Feb 2026 17:28:46 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2026-23189: ceph: fix NULL pointer dereference in ceph_mds_auth_match()

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

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

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

ceph: fix NULL pointer dereference in ceph_mds_auth_match()

The CephFS kernel client has regression starting from 6.18-rc1.
We have issue in ceph_mds_auth_match() if fs_name == NULL:

    const char fs_name = mdsc->fsc->mount_options->mds_namespace;
    ...
    if (auth->match.fs_name && strcmp(auth->match.fs_name, fs_name)) {
            / fsname mismatch, try next one */
            return 0;
    }

Patrick Donnelly suggested that: In summary, we should definitely start
decoding `fs_name` from the MDSMap and do strict authorizations checks
against it. Note that the `-o mds_namespace=foo` should only be used for
selecting the file system to mount and nothing else. It's possible
no mds_namespace is specified but the kernel will mount the only
file system that exists which may have name "foo".

This patch reworks ceph_mdsmap_decode() and namespace_equals() with
the goal of supporting the suggested concept. Now struct ceph_mdsmap
contains m_fs_name field that receives copy of extracted FS name
by ceph_extract_encoded_string(). For the case of "old" CephFS file
systems, it is used "cephfs" name.

[ idryomov: replace redundant %*pE with %s in ceph_mdsmap_decode(),
  get rid of a series of strlen() calls in ceph_namespace_match(),
  drop changes to namespace_equals() body to avoid treating empty
  mds_namespace as equal, drop changes to ceph_mdsc_handle_fsmap()
  as namespace_equals() isn't an equivalent substitution there ]

The Linux kernel CVE team has assigned CVE-2026-23189 to this issue.


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

	Issue introduced in 6.12.58 with commit 07640d34a781bb2e39020a39137073c03c4aa932 and fixed in 6.12.70 with commit c6f8326f26bd20d648d9a55afd68148d1b6afe28
	Issue introduced in 6.18 with commit 22c73d52a6d05c5a2053385c0d6cd9984732799d and fixed in 6.18.10 with commit 57b36ffc8881dd455d875f85c105901974af2130
	Issue introduced in 6.18 with commit 22c73d52a6d05c5a2053385c0d6cd9984732799d and fixed in 6.19 with commit 7987cce375ac8ce98e170a77aa2399f2cf6eb99f
	Issue introduced in 6.17.8 with commit ca3da8b27ab9a0923ad477447cfb8fc7f4b4c523

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-2026-23189
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/ceph/mds_client.c
	fs/ceph/mdsmap.c
	fs/ceph/mdsmap.h
	fs/ceph/super.h
	include/linux/ceph/ceph_fs.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/c6f8326f26bd20d648d9a55afd68148d1b6afe28
	https://git.kernel.org/stable/c/57b36ffc8881dd455d875f85c105901974af2130
	https://git.kernel.org/stable/c/7987cce375ac8ce98e170a77aa2399f2cf6eb99f