| From 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071 Mon Sep 17 00:00:00 2001 |
| From: Eric Dumazet <edumazet@google.com> |
| Date: Wed, 26 Oct 2016 09:27:57 -0700 |
| Subject: tcp/dccp: drop SYN packets if accept queue is full |
| |
| From: Eric Dumazet <edumazet@google.com> |
| |
| commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071 upstream. |
| |
| 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> |
| Signed-off-by: Arnd Bergmann <arnd@arndb.de> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| include/net/inet_connection_sock.h | 5 ----- |
| net/dccp/ipv4.c | 8 +------- |
| net/dccp/ipv6.c | 2 +- |
| net/ipv4/tcp_input.c | 8 +------- |
| 4 files changed, 3 insertions(+), 20 deletions(-) |
| |
| --- a/include/net/inet_connection_sock.h |
| +++ b/include/net/inet_connection_sock.h |
| @@ -289,11 +289,6 @@ static inline int inet_csk_reqsk_queue_l |
| 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; |
| --- a/net/dccp/ipv4.c |
| +++ b/net/dccp/ipv4.c |
| @@ -596,13 +596,7 @@ int dccp_v4_conn_request(struct sock *sk |
| 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); |
| --- a/net/dccp/ipv6.c |
| +++ b/net/dccp/ipv6.c |
| @@ -328,7 +328,7 @@ static int dccp_v6_conn_request(struct s |
| 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); |
| --- a/net/ipv4/tcp_input.c |
| +++ b/net/ipv4/tcp_input.c |
| @@ -6374,13 +6374,7 @@ int tcp_conn_request(struct request_sock |
| 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; |
| } |
