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 [email protected]=/ /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 [email protected]=/ /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" ]

Link: https://tracker.ceph.com/issues/72167
Signed-off-by: Kotresh HR <[email protected]>
Reviewed-by: Viacheslav Dubeyko <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>

Author: kotreshhr

fs/ceph/mds_client.c

@@ -5655,11 +5655,19 @@ static int ceph_mds_auth_match(struct ceph_mds_client *mdsc,
 	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 *spath = mdsc->fsc->mount_options->server_path;
 	bool gid_matched = false;
 	u32 gid, tlen, len;
 	int i, j;
 
+	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)) {
+		/* fsname mismatch, try next one */
+		return 0;
+	}
+
 	doutc(cl, "match.uid %lld\n", auth->match.uid);
 	if (auth->match.uid != MDS_AUTH_UID_ANY) {
 		if (auth->match.uid != caller_uid)

fs/ceph/mdsmap.c

@@ -353,10 +353,22 @@ struct ceph_mdsmap *ceph_mdsmap_decode(struct ceph_mds_client *mdsc, void **p,
 		__decode_and_drop_type(p, end, u8, bad_ext);
 	}
 	if (mdsmap_ev >= 8) {
+		u32 fsname_len;
 		/* enabled */
 		ceph_decode_8_safe(p, end, m->m_enabled, bad_ext);
 		/* fs_name */
-		ceph_decode_skip_string(p, end, bad_ext);
+		ceph_decode_32_safe(p, end, fsname_len, bad_ext);
+
+		/* validate fsname against mds_namespace */
+		if (!namespace_equals(mdsc->fsc->mount_options, *p,
+				      fsname_len)) {
+			pr_warn_client(cl, "fsname %*pE doesn't match mds_namespace %s\n",
+				       (int)fsname_len, (char *)*p,
+				       mdsc->fsc->mount_options->mds_namespace);
+			goto bad;
+		}
+		/* skip fsname after validation */
+		ceph_decode_skip_n(p, end, fsname_len, bad);
 	}
 	/* damaged */
 	if (mdsmap_ev >= 9) {

fs/ceph/super.c

@@ -246,20 +246,6 @@ static void canonicalize_path(char *path)
 	path[j] = '\0';
 }
 
-/*
- * 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 int namespace_equals(struct ceph_mount_options *fsopt,
-			    const char *namespace, size_t len)
-{
-	return !(fsopt->mds_namespace &&
-		 (strlen(fsopt->mds_namespace) != len ||
-		  strncmp(fsopt->mds_namespace, namespace, len)));
-}
-
 static int ceph_parse_old_source(const char *dev_name, const char *dev_name_end,
 				 struct fs_context *fc)
 {

fs/ceph/super.h

@@ -104,6 +104,20 @@ struct ceph_mount_options {
 	struct fscrypt_dummy_policy dummy_enc_policy;
 };
 
+/*
+ * 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)
+{
+	return !(fsopt->mds_namespace &&
+		 (strlen(fsopt->mds_namespace) != len ||
+		  strncmp(fsopt->mds_namespace, namespace, len)));
+}
+
 /* mount state */
 enum {
 	CEPH_MOUNT_MOUNTING,