apparmor: increase left match history buffer size

There have been cases reported where a history buffer size of 8 was
not enough to resolve conflict overlaps. Increase the buffer to and
get rid of the size element which is currently just storing the
constant WB_HISTORY_SIZE.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/match.h

@@ -138,7 +138,7 @@ unsigned int aa_dfa_matchn_until(struct aa_dfa *dfa, unsigned int start,
 
 void aa_dfa_free_kref(struct kref *kref);
 
-#define WB_HISTORY_SIZE 8
+#define WB_HISTORY_SIZE 24
 struct match_workbuf {
 	unsigned int count;
 	unsigned int pos;
@@ -151,7 +151,6 @@ struct match_workbuf N = {		\
 	.count = 0,			\
 	.pos = 0,			\
 	.len = 0,			\
-	.size = WB_HISTORY_SIZE,			\
 }
 
 unsigned int aa_dfa_leftmatch(struct aa_dfa *dfa, unsigned int start,

security/apparmor/match.c

@@ -620,8 +620,8 @@ unsigned int aa_dfa_matchn_until(struct aa_dfa *dfa, unsigned int start,
 
 #define inc_wb_pos(wb)						\
 do {								\
-	wb->pos = (wb->pos + 1) & (wb->size - 1);		\
-	wb->len = (wb->len + 1) & (wb->size - 1);		\
+	wb->pos = (wb->pos + 1) & (WB_HISTORY_SIZE - 1);		\
+	wb->len = (wb->len + 1) & (WB_HISTORY_SIZE - 1);		\
 } while (0)
 
 /* For DFAs that don't support extended tagging of states */
@@ -640,7 +640,7 @@ static bool is_loop(struct match_workbuf *wb, unsigned int state,
 			return true;
 		}
 		if (pos == 0)
-			pos = wb->size;
+			pos = WB_HISTORY_SIZE;
 		pos--;
 	}