tcp: refine sk_rcvbuf increase for ooo packets

When a passive flow has not been accepted yet, it is
not wise to increase sk_rcvbuf when receiving ooo packets.

A very busy server might tune down tcp_rmem[1] to better
control how much memory can be used by sockets waiting
in its listeners accept queues.

Fixes: 63ad7df ("tcp: adjust rcvbuf in presence of reorders")
Signed-off-by: Eric Dumazet <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

net/ipv4/tcp_input.c

@@ -5181,7 +5181,9 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 		skb_condense(skb);
 		skb_set_owner_r(skb, sk);
 	}
-	tcp_rcvbuf_grow(sk);
+	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
+	if (sk->sk_socket)
+		tcp_rcvbuf_grow(sk);
 }
 
 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,