linux-cve-announce - CVE-2025-40362: ceph: fix multifs mds auth caps issue

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Message-ID: <2025121645-CVE-2025-40362-c4d6@gregkh>
Date: Tue, 16 Dec 2025 14:40:48 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40362: ceph: fix multifs mds auth caps issue

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

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

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

ceph: fix multifs mds auth caps issue

The mds auth caps check should also validate the
fsname along with the associated caps. Not doing
so would result in applying the mds auth caps of
one fs on to the other fs in a multifs ceph cluster.
The bug causes multiple issues w.r.t user
authentication, following is one such example.

Steps to Reproduce (on vstart cluster):
1. Create two file systems in a cluster, say 'fsname1' and 'fsname2'
2. Authorize read only permission to the user 'client.usr' on fs 'fsname1'
    $ceph fs authorize fsname1 client.usr / r
3. Authorize read and write permission to the same user 'client.usr' on fs 'fsname2'
    $ceph fs authorize fsname2 client.usr / rw
4. Update the keyring
    $ceph auth get client.usr >> ./keyring

With above permssions for the user 'client.usr', following is the
expectation.
  a. The 'client.usr' should be able to only read the contents
     and not allowed to create or delete files on file system 'fsname1'.
  b. The 'client.usr' should be able to read/write on file system 'fsname2'.

But, with this bug, the 'client.usr' is allowed to read/write on file
system 'fsname1'. See below.

5. Mount the file system 'fsname1' with the user 'client.usr'
     $sudo bin/mount.ceph usr@...name1=/ /kmnt_fsname1_usr/
6. Try creating a file on file system 'fsname1' with user 'client.usr'. This
   should fail but passes with this bug.
     $touch /kmnt_fsname1_usr/file1
7. Mount the file system 'fsname1' with the user 'client.admin' and create a
   file.
     $sudo bin/mount.ceph admin@...name1=/ /kmnt_fsname1_admin
     $echo "data" > /kmnt_fsname1_admin/admin_file1
8. Try removing an existing file on file system 'fsname1' with the user
   'client.usr'. This shoudn't succeed but succeeds with the bug.
     $rm -f /kmnt_fsname1_usr/admin_file1

For more information, please take a look at the corresponding mds/fuse patch
and tests added by looking into the tracker mentioned below.

v2: Fix a possible null dereference in doutc
v3: Don't store fsname from mdsmap, validate against
    ceph_mount_options's fsname and use it
v4: Code refactor, better warning message and
    fix possible compiler warning

[ Slava.Dubeyko: "fsname check failed" -> "fsname mismatch" ]

The Linux kernel CVE team has assigned CVE-2025-40362 to this issue.


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

	Fixed in 6.12.58 with commit 07640d34a781bb2e39020a39137073c03c4aa932
	Fixed in 6.17.8 with commit ca3da8b27ab9a0923ad477447cfb8fc7f4b4c523
	Fixed in 6.18 with commit 22c73d52a6d05c5a2053385c0d6cd9984732799d

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-2025-40362
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/super.c
	fs/ceph/super.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/07640d34a781bb2e39020a39137073c03c4aa932
	https://git.kernel.org/stable/c/ca3da8b27ab9a0923ad477447cfb8fc7f4b4c523
	https://git.kernel.org/stable/c/22c73d52a6d05c5a2053385c0d6cd9984732799d