[PATCH 6.12 012/113] ceph: fix NULL pointer dereference in ceph_mds_auth_match()

Greg Kroah-Hartman
2026-02-09T14:35:29Z

From: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>

commit 7987cce375ac8ce98e170a77aa2399f2cf6eb99f upstream.

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 ]

Cc: stable@vger.kernel.org
Fixes: 22c73d52a6d0 ("ceph: fix multifs mds auth caps issue")
Link: https://tracker.ceph.com/issues/73886
Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Patrick Donnelly <pdonnell@ibm.com>
Tested-by: Patrick Donnelly <pdonnell@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ceph/mds_client.c | 5 +++--
fs/ceph/mdsmap.c | 26 +++++++++++++++++++-------
fs/ceph/mdsmap.h | 1 +
fs/ceph/super.h | 16 ++++++++++++++--
include/linux/ceph/ceph_fs.h | 6 ++++++
5 files changed, 43 insertions(+), 11 deletions(-)

--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -5652,7 +5652,7 @@ static int ceph_mds_auth_match(struct ce
u32 caller_uid = from_kuid(&init_user_ns, cred->fsuid);
u32 caller_gid = from_kgid(&init_user_ns, cred->fsgid);
struct ceph_client *cl = mdsc->fsc->client;
- const char *fs_name = mdsc->fsc->mount_options->mds_namespace;
+ const char *fs_name = mdsc->mdsmap->m_fs_name;
const char *spath = mdsc->fsc->mount_options->server_path;
bool gid_matched = false;
u32 gid, tlen, len;
@@ -5660,7 +5660,8 @@ static int ceph_mds_auth_match(struct ce

doutc(cl, "fsname check fs_name=%s match.fs_name=%s\n",
fs_name, auth->match.fs_name ? auth->match.fs_name : "");
- if (auth->match.fs_name && strcmp(auth->match.fs_name, fs_name)) {
+
+ if (!ceph_namespace_match(auth->match.fs_name, fs_name)) {
/* fsname mismatch, try next one */
return 0;
}
--- a/fs/ceph/mdsmap.c
+++ b/fs/ceph/mdsmap.c
@@ -353,22 +353,33 @@ struct ceph_mdsmap *ceph_mdsmap_decode(s
__decode_and_drop_type(p, end, u8, bad_ext);
}
if (mdsmap_ev >= 8) {
- u32 fsname_len;
+ size_t fsname_len;
+
/* enabled */
ceph_decode_8_safe(p, end, m->m_enabled, bad_ext);
+
/* fs_name */
- ceph_decode_32_safe(p, end, fsname_len, bad_ext);
+ m->m_fs_name = ceph_extract_encoded_string(p, end,
+ &fsname_len,
+ GFP_NOFS);
+ if (IS_ERR(m->m_fs_name)) {
+ m->m_fs_name = NULL;
+ goto nomem;
+ }

/* validate fsname against mds_namespace */
- if (!namespace_equals(mdsc->fsc->mount_options, *p,
+ if (!namespace_equals(mdsc->fsc->mount_options, m->m_fs_name,
fsname_len)) {
- pr_warn_client(cl, "fsname %*pE doesn't match mds_namespace %s\n",
- (int)fsname_len, (char *)*p,
+ pr_warn_client(cl, "fsname %s doesn't match mds_namespace %s\n",
+ m->m_fs_name,
mdsc->fsc->mount_options->mds_namespace);
goto bad;
}
- /* skip fsname after validation */
- ceph_decode_skip_n(p, end, fsname_len, bad);
+ } else {
+ m->m_enabled = false;
+ m->m_fs_name = kstrdup(CEPH_OLD_FS_NAME, GFP_NOFS);
+ if (!m->m_fs_name)
+ goto nomem;
}
/* damaged */
if (mdsmap_ev >= 9) {
@@ -430,6 +441,7 @@ void ceph_mdsmap_destroy(struct ceph_mds
kfree(m->m_info);
}
kfree(m->m_data_pg_pools);
+ kfree(m->m_fs_name);
kfree(m);
}

--- a/fs/ceph/mdsmap.h
+++ b/fs/ceph/mdsmap.h
@@ -45,6 +45,7 @@ struct ceph_mdsmap {
bool m_enabled;
bool m_damaged;
int m_num_laggy;
+ char *m_fs_name;
};

static inline struct ceph_entity_addr *
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -104,14 +104,26 @@ struct ceph_mount_options {
struct fscrypt_dummy_policy dummy_enc_policy;
};

+#define CEPH_NAMESPACE_WILDCARD "*"
+
+static inline bool ceph_namespace_match(const char *pattern,
+ const char *target)
+{
+ if (!pattern || !pattern[0] ||
+ !strcmp(pattern, CEPH_NAMESPACE_WILDCARD))
+ return true;
+
+ return !strcmp(pattern, target);
+}
+
/*
* Check if the mds namespace in ceph_mount_options matches
* the passed in namespace string. First time match (when
* ->mds_namespace is NULL) is treated specially, since
* ->mds_namespace needs to be initialized by the caller.
*/
-static inline int namespace_equals(struct ceph_mount_options *fsopt,
- const char *namespace, size_t len)
+static inline bool namespace_equals(struct ceph_mount_options *fsopt,
+ const char *namespace, size_t len)
{
return !(fsopt->mds_namespace &&
(strlen(fsopt->mds_namespace) != len ||
--- a/include/linux/ceph/ceph_fs.h
+++ b/include/linux/ceph/ceph_fs.h
@@ -31,6 +31,12 @@
#define CEPH_INO_CEPH 2 /* hidden .ceph dir */
#define CEPH_INO_GLOBAL_SNAPREALM 3 /* global dummy snaprealm */

+/*
+ * name for "old" CephFS file systems,
+ * see ceph.git e2b151d009640114b2565c901d6f41f6cd5ec652
+ */
+#define CEPH_OLD_FS_NAME "cephfs"
+
/* arbitrary limit on max # of monitors (cluster of 3 is typical) */
#define CEPH_MAX_MON 31