tipc: fix unique bearer names sanity check

When enabling a bearer by name, we don't sanity check its name with
higher slot in bearer list. This may have the effect that the name
of an already enabled bearer bypasses the check.

To fix the above issue, we just perform an extra checking with all
existing bearers.

Fixes: cb30a633 ("tipc: refactor function tipc_enable_bearer()")
Cc: stable@vger.kernel.org
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Hoang Le <hoang.h.le@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/bearer.c

@@ -256,6 +256,7 @@ static int tipc_enable_bearer(struct net *net, const char *name,
 	int bearer_id = 0;
 	int res = -EINVAL;
 	char *errstr = "";
+	u32 i;
 
 	if (!bearer_name_validate(name, &b_names)) {
 		errstr = "illegal name";
@@ -280,31 +281,38 @@ static int tipc_enable_bearer(struct net *net, const char *name,
 		prio = m->priority;
 
 	/* Check new bearer vs existing ones and find free bearer id if any */
-	while (bearer_id < MAX_BEARERS) {
-		b = rtnl_dereference(tn->bearer_list[bearer_id]);
-		if (!b)
-			break;
+	bearer_id = MAX_BEARERS;
+	i = MAX_BEARERS;
+	while (i-- != 0) {
+		b = rtnl_dereference(tn->bearer_list[i]);
+		if (!b) {
+			bearer_id = i;
+			continue;
+		}
 		if (!strcmp(name, b->name)) {
 			errstr = "already enabled";
 			NL_SET_ERR_MSG(extack, "Already enabled");
 			goto rejected;
 		}
-		bearer_id++;
-		if (b->priority != prio)
-			continue;
-		if (++with_this_prio <= 2)
-			continue;
-		pr_warn("Bearer <%s>: already 2 bearers with priority %u\n",
-			name, prio);
-		if (prio == TIPC_MIN_LINK_PRI) {
-			errstr = "cannot adjust to lower";
-			NL_SET_ERR_MSG(extack, "Cannot adjust to lower");
-			goto rejected;
+
+		if (b->priority == prio &&
+		    (++with_this_prio > 2)) {
+			pr_warn("Bearer <%s>: already 2 bearers with priority %u\n",
+				name, prio);
+
+			if (prio == TIPC_MIN_LINK_PRI) {
+				errstr = "cannot adjust to lower";
+				NL_SET_ERR_MSG(extack, "Cannot adjust to lower");
+				goto rejected;
+			}
+
+			pr_warn("Bearer <%s>: trying with adjusted priority\n",
+				name);
+			prio--;
+			bearer_id = MAX_BEARERS;
+			i = MAX_BEARERS;
+			with_this_prio = 1;
 		}
-		pr_warn("Bearer <%s>: trying with adjusted priority\n", name);
-		prio--;
-		bearer_id = 0;
-		with_this_prio = 1;
 	}
 
 	if (bearer_id >= MAX_BEARERS) {