[PATCH net-next 2/4] tcp: mitigate ACK loops for connections as tcp_request_sock
flat view
STALE4285d
From: Neal Cardwell <ncardwell@google.com>
Date: 2015-02-06 21:05:50
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
In the SYN_RECV state, where the TCP connection is represented by tcp_request_sock, we now rate-limit SYNACKs in response to a client's retransmitted SYNs: we do not send a SYNACK in response to client SYN if it has been less than sysctl_tcp_invalid_ratelimit (default 500ms) since we last sent a SYNACK in response to a client's retransmitted SYN. This allows the vast majority of legitimate client connections to proceed unimpeded, even for the most aggressive platforms, iOS and MacOS, which actually retransmit SYNs 1-second intervals for several times in a row. They use SYN RTO timeouts following the progression: 1,1,1,1,1,2,4,8,16,32. Reported-by: Avery Fay <redacted> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <redacted> Signed-off-by: Eric Dumazet <redacted> --- include/linux/tcp.h | 1 + include/net/tcp.h | 1 + net/ipv4/tcp_minisocks.c | 6 +++++- 3 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 67309ec..bcc828d 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h@@ -115,6 +115,7 @@ struct tcp_request_sock { u32 rcv_isn; u32 snt_isn; u32 snt_synack; /* synack sent time */ + u32 last_oow_ack_time; /* last SYNACK */ u32 rcv_nxt; /* the ack # by SYNACK. For * FastOpen it's the seq# * after data-in-SYN.
diff --git a/include/net/tcp.h b/include/net/tcp.h
index b81f45c..da4196fb 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h@@ -1145,6 +1145,7 @@ static inline void tcp_openreq_init(struct request_sock *req, tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq; tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; tcp_rsk(req)->snt_synack = tcp_time_stamp; + tcp_rsk(req)->last_oow_ack_time = 0; req->mss = rx_opt->mss_clamp; req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0; ireq->tstamp_ok = rx_opt->tstamp_ok;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index bc9216d..131aa49 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c@@ -605,7 +605,11 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, * Reset timer after retransmitting SYNACK, similar to * the idea of fast retransmit in recovery. */ - if (!inet_rtx_syn_ack(sk, req)) + if (!tcp_oow_rate_limited(sock_net(sk), skb, + LINUX_MIB_TCPACKSKIPPEDSYNRECV, + &tcp_rsk(req)->last_oow_ack_time) && + + !inet_rtx_syn_ack(sk, req)) req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX) + jiffies; return NULL;
--
2.2.0.rc0.207.ga3a616c