From 702d673e9e74de360a9635536b8ac3bd1a48bb68 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 26 Oct 2016 09:27:57 -0700 Subject: [PATCH] BACKPORT: 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 Acked-by: Neal Cardwell Acked-by: Yuchung Cheng Signed-off-by: David S. Miller (cherry picked from commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071) Backport for pass Android CTS CtsLibcoreTestCases: libcore.javax.net.ServerSocketFactoryTest#testCreateServerSocketWithPortNoBacklog Refer the comments on libcore/luni/src/test/java/libcore/javax/net/ServerSocketFactoryTest.java // This test may fail on kernel versions between 4.4 and 4.9, due to a kernel implementation // detail change. Backporting the following kernel change will fix the behavior. // http://b/31960002 // https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071 public void testCreateServerSocketWithPortNoBacklog() throws IOException { ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(0, 1); testSocket(serverSocket, 1); } Change-Id: I9bb3531480f4942447d8d4eded110aa31bc7c031 Signed-off-by: Tao Huang --- 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(-) diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h index 49dcad4fe99e..72599bbc8255 100644 --- 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_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; diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c index 6eb2bbf9873b..f5f794a048e4 100644 --- a/net/dccp/ipv4.c +++ b/net/dccp/ipv4.c @@ -592,13 +592,7 @@ 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); diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c index 09a9ab65f4e1..a27b75ca90e3 100644 --- a/net/dccp/ipv6.c +++ b/net/dccp/ipv6.c @@ -324,7 +324,7 @@ 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); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index f409a12d6ec1..1d7eb209b4ae 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6188,13 +6188,7 @@ 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_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); goto drop; }