apparmor: add missing id bounds check on dfa verification

Signed-off-by: NJohn Johansen <john.johansen@canonical.com>

security/apparmor/include/match.h

@@ -62,6 +62,7 @@ struct table_set_header {
 #define YYTD_ID_ACCEPT2 6
 #define YYTD_ID_NXT	7
 #define YYTD_ID_TSIZE	8
+#define YYTD_ID_MAX	8
 
 #define YYTD_DATA8	1
 #define YYTD_DATA16	2

security/apparmor/match.c

@@ -47,6 +47,8 @@ static struct table_header *unpack_table(char *blob, size_t bsize)
 	 * it every time we use td_id as an index
 	 */
 	th.td_id = be16_to_cpu(*(u16 *) (blob)) - 1;
+	if (th.td_id > YYTD_ID_MAX)
+		goto out;
 	th.td_flags = be16_to_cpu(*(u16 *) (blob + 2));
 	th.td_lolen = be32_to_cpu(*(u32 *) (blob + 8));
 	blob += sizeof(struct table_header);