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 ]

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>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
index c7f2c63b3bc3..08e5dbe15ca4 100644
--- 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