apparmor: add a valid state flags check

Add a check to ensure only known state flags are set on each
state in the dfa.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/match.h

@@ -181,5 +181,9 @@ static inline void aa_put_dfa(struct aa_dfa *dfa)
 
 #define MATCH_FLAG_DIFF_ENCODE 0x80000000
 #define MARK_DIFF_ENCODE 0x40000000
+#define MATCH_FLAG_OOB_TRANSITION 0x20000000
+#define MATCH_FLAGS_MASK 0xff000000
+#define MATCH_FLAGS_VALID MATCH_FLAG_DIFF_ENCODE
+#define MATCH_FLAGS_INVALID (MATCH_FLAGS_MASK & ~MATCH_FLAGS_VALID)
 
 #endif /* __AA_MATCH_H */

security/apparmor/match.c

@@ -202,6 +202,10 @@ static int verify_dfa(struct aa_dfa *dfa)
 		if (!(BASE_TABLE(dfa)[i] & MATCH_FLAG_DIFF_ENCODE) &&
 		    (DEFAULT_TABLE(dfa)[i] >= state_count))
 			goto out;
+		if (BASE_TABLE(dfa)[i] & MATCH_FLAGS_INVALID) {
+			pr_err("AppArmor DFA state with invalid match flags");
+			goto out;
+		}
 		if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
 			pr_err("AppArmor DFA next/check upper bounds error\n");
 			goto out;