tipc: fix correct setting of message type in second discoverer

The duplicate address discovery protocol is not safe against two
discoverers running in parallel. The one executing first after the
trial period is over will set the node address and change its own
message type to DSC_REQ_MSG. The one executing last may find that the
node address is already set, and never change message type, with the
result that its links may never be established.

In this commmit we ensure that the message type always is set correctly
after the trial period is over.

Fixes: 25b0b9c4 ("tipc: handle collisions of 32-bit node address hash values")
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/discover.c

@@ -287,7 +287,6 @@ static void tipc_disc_timeout(struct timer_list *t)
 {
 	struct tipc_discoverer *d = from_timer(d, t, timer);
 	struct tipc_net *tn = tipc_net(d->net);
-	u32 self = tipc_own_addr(d->net);
 	struct tipc_media_addr maddr;
 	struct sk_buff *skb = NULL;
 	struct net *net = d->net;
@@ -301,12 +300,14 @@ static void tipc_disc_timeout(struct timer_list *t)
 		goto exit;
 	}
 
-	/* Did we just leave the address trial period ? */
-	if (!self && !time_before(jiffies, tn->addr_trial_end)) {
-		self = tn->trial_addr;
-		tipc_net_finalize(net, self);
-		msg_set_prevnode(buf_msg(d->skb), self);
+	/* Trial period over ? */
+	if (!time_before(jiffies, tn->addr_trial_end)) {
+		/* Did we just leave it ? */
+		if (!tipc_own_addr(net))
+			tipc_net_finalize(net, tn->trial_addr);
+
 		msg_set_type(buf_msg(d->skb), DSC_REQ_MSG);
+		msg_set_prevnode(buf_msg(d->skb), tipc_own_addr(net));
 	}
 
 	/* Adjust timeout interval according to discovery phase */