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authorNeal Cardwell <ncardwell@google.com>2015-02-06 16:04:39 -0500
committerDavid S. Miller <davem@davemloft.net>2015-02-08 01:03:12 -0800
commita9b2c06dbef48ed31cff1764c5ce824829106f4f (patch)
tree7e1dc6d03d3f2ba41a3a867fad3bf59c49665599
parent032ee4236954eb214651cb9bfc1b38ffa8fd7a01 (diff)
tcp: mitigate ACK loops for connections as tcp_request_sock
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 <avery@mixpanel.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/tcp.h1
-rw-r--r--include/net/tcp.h1
-rw-r--r--net/ipv4/tcp_minisocks.c6
3 files changed, 7 insertions, 1 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 67309ece0772..bcc828d3b9b9 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 b81f45c67b2e..da4196fb78db 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 bc9216dc9de1..131aa4950d1c 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;