Commit 5ea8ea2c authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp/dccp: drop SYN packets if accept queue is full 



Per listen(fd, backlog) rules, there is really no point accepting a SYN,
sending a SYNACK, and dropping the following ACK packet if accept queue
is full, because application is not draining accept queue fast enough.

This behavior is fooling TCP clients that believe they established a
flow, while there is nothing at server side. They might then send about
10 MSS (if using IW10) that will be dropped anyway while server is under
stress.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Acked-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 58effd71

include/net/inet_connection_sock.h

+0 −5
Original line number Diff line number Diff line
@@ -289,11 +289,6 @@ static inline int inet_csk_reqsk_queue_len(const struct sock *sk) 
	return reqsk_queue_len(&inet_csk(sk)->icsk_accept_queue);

}



static inline int inet_csk_reqsk_queue_young(const struct sock *sk)

{

	return reqsk_queue_len_young(&inet_csk(sk)->icsk_accept_queue);

}



static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)

{

	return inet_csk_reqsk_queue_len(sk) >= sk->sk_max_ack_backlog;

net/dccp/ipv4.c

+1 −7
Original line number Diff line number Diff line
@@ -588,13 +588,7 @@ int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb) 
	if (inet_csk_reqsk_queue_is_full(sk))

		goto drop;



	/*

	 * Accept backlog is full. If we have already queued enough

	 * of warm entries in syn queue, drop request. It is better than

	 * clogging syn queue with openreqs with exponentially increasing

	 * timeout.

	 */

	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)

	if (sk_acceptq_is_full(sk))

		goto drop;



	req = inet_reqsk_alloc(&dccp_request_sock_ops, sk, true);

net/dccp/ipv6.c

+1 −1
Original line number Diff line number Diff line
@@ -325,7 +325,7 @@ static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb) 
	if (inet_csk_reqsk_queue_is_full(sk))

		goto drop;



	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)

	if (sk_acceptq_is_full(sk))

		goto drop;



	req = inet_reqsk_alloc(&dccp6_request_sock_ops, sk, true);

net/ipv4/tcp_input.c

+1 −7
Original line number Diff line number Diff line
@@ -6298,13 +6298,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, 
			goto drop;

	}





	/* Accept backlog is full. If we have already queued enough

	 * of warm entries in syn queue, drop request. It is better than

	 * clogging syn queue with openreqs with exponentially increasing

	 * timeout.

	 */

	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {

	if (sk_acceptq_is_full(sk)) {

		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);

		goto drop;

	}

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