inet: fix races in reqsk_queue_hash_req()

Before allowing lockless LISTEN processing, we need to make
sure to arm the SYN_RECV timer before the req socket is visible
in hash tables.

Also, req->rsk_hash should be written before we set rsk_refcnt
to a non zero value.

Fixes: fa76ce7328 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ying Cai <ycai@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -685,20 +685,20 @@ void reqsk_queue_hash_req(struct request_sock_queue *queue,
 	req->num_timeout = 0;
 	req->sk = NULL;
 
+	setup_timer(&req->rsk_timer, reqsk_timer_handler, (unsigned long)req);
+	mod_timer_pinned(&req->rsk_timer, jiffies + timeout);
+	req->rsk_hash = hash;
+
 	/* before letting lookups find us, make sure all req fields
 	 * are committed to memory and refcnt initialized.
 	 */
 	smp_wmb();
 	atomic_set(&req->rsk_refcnt, 2);
-	setup_timer(&req->rsk_timer, reqsk_timer_handler, (unsigned long)req);
-	req->rsk_hash = hash;
 
 	spin_lock(&queue->syn_wait_lock);
 	req->dl_next = lopt->syn_table[hash];
 	lopt->syn_table[hash] = req;
 	spin_unlock(&queue->syn_wait_lock);
-
-	mod_timer_pinned(&req->rsk_timer, jiffies + timeout);
 }
 EXPORT_SYMBOL(reqsk_queue_hash_req);