tcp: Fix use-after-free of nreq in reqsk_timer_handler().

The cited commit replaced inet_csk_reqsk_queue_drop_and_put() with
__inet_csk_reqsk_queue_drop() and reqsk_put() in reqsk_timer_handler().

Then, oreq should be passed to reqsk_put() instead of req; otherwise
use-after-free of nreq could happen when reqsk is migrated but the
retry attempt failed (e.g. due to timeout).

Let's pass oreq to reqsk_put().

Fixes: e8c526f ("tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().")
Reported-by: Liu Jian <[email protected]>
Closes: https://lore.kernel.org/netdev/[email protected]/
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: Vadim Fedorenko <[email protected]>
Reviewed-by: Liu Jian <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Reviewed-by: Martin KaFai Lau <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: q2ven

net/ipv4/inet_connection_sock.c

@@ -1191,7 +1191,7 @@ static void reqsk_timer_handler(struct timer_list *t)
 
 drop:
 	__inet_csk_reqsk_queue_drop(sk_listener, oreq, true);
-	reqsk_put(req);
+	reqsk_put(oreq);
 }
 
 static bool reqsk_queue_hash_req(struct request_sock *req,