ceph: fix decoding of client session messages flags

commit ea16567 upstream.

The cephfs kernel client started to show  the message:

 ceph: mds0 session blocklisted

when mounting a filesystem.  This is due to the fact that the session
messages are being incorrectly decoded: the skip needs to take into
account the 'len'.

While there, fixed some whitespaces too.

Cc: stable@vger.kernel.org
Fixes: e1c9788 ("ceph: don't rely on error_string to validate blocklisted session.")
Signed-off-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ceph/mds_client.c

@@ -3378,13 +3378,17 @@ static void handle_session(struct ceph_mds_session *session,
 	}
 
 	if (msg_version >= 5) {
-		u32 flags;
-		/* version >= 4, struct_v, struct_cv, len, metric_spec */
-	        ceph_decode_skip_n(&p, end, 2 + sizeof(u32) * 2, bad);
+		u32 flags, len;
+
+		/* version >= 4 */
+		ceph_decode_skip_16(&p, end, bad); /* struct_v, struct_cv */
+		ceph_decode_32_safe(&p, end, len, bad); /* len */
+		ceph_decode_skip_n(&p, end, len, bad); /* metric_spec */
+
 		/* version >= 5, flags   */
-                ceph_decode_32_safe(&p, end, flags, bad);
+		ceph_decode_32_safe(&p, end, flags, bad);
 		if (flags & CEPH_SESSION_BLOCKLISTED) {
-		        pr_warn("mds%d session blocklisted\n", session->s_mds);
+			pr_warn("mds%d session blocklisted\n", session->s_mds);
 			blocklisted = true;
 		}
 	}