4.4-stable review patch. If anyone has any objections, please let me know.
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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 @@ -592,13 +592,7 @@ 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 @@ -324,7 +324,7 @@ 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 @@ -6305,13 +6305,7 @@ 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_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); goto drop; }