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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: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-10-26 09:27:57 -07:00 committed by David S. Miller
parent 58effd7168
commit 5ea8ea2cb7
4 changed files with 3 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/net/inet_connection_sock.h
View File

@ -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;

8
net/dccp/ipv4.c
View File

@ -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);

2
net/dccp/ipv6.c
View File

@ -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);

8
net/ipv4/tcp_input.c
View File

@ -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;
}