From f50af12068d0af529acdaa4e45f0d4acc8c372d1 Mon Sep 17 00:00:00 2001 From: Michael Tremer Date: Fri, 11 Mar 2022 11:08:10 +0000 Subject: [PATCH] stream: tcp: Handle retransmitted SYN with TSval For connections that use TCP timestamps for which the first SYN packet does not reach the server, any replies to retransmitted SYNs will be tropped. This is happening in StateSynSentValidateTimestamp, where the timestamp value in a SYN-ACK packet must match the one from the SYN packet. However, since the server never received the first SYN packet, it will respond with an updated timestamp from any of the following SYN packets. The timestamp value inside suricata is not being updated at any time which should happen. This patch fixes that problem. Bug: #4376. Signed-off-by: Michael Tremer --- src/stream-tcp.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/src/stream-tcp.c b/src/stream-tcp.c index 8d1226aa3c..d0d770f39c 100644 --- a/src/stream-tcp.c +++ b/src/stream-tcp.c @@ -1647,6 +1647,24 @@ static int StreamTcpPacketStateSynSent(ThreadVars *tv, Packet *p, "ssn->client.last_ack %"PRIu32"", ssn, ssn->client.isn, ssn->client.next_seq, ssn->client.last_ack); + } else if (PKT_IS_TOSERVER(p)) { + /* + * On retransmitted SYN packets, the timestamp value must be updated, + * to avoid dropping any SYN+ACK packets that respond to a retransmitted SYN + * with an updated timestamp in StateSynSentValidateTimestamp. + */ + if ((ssn->client.flags & STREAMTCP_STREAM_FLAG_TIMESTAMP) && TCP_HAS_TS(p)) { + uint32_t ts_val = TCP_GET_TSVAL(p); + + // Check whether packets have been received in the correct order (only ever update) + if (ssn->client.last_ts < ts_val) { + ssn->client.last_ts = ts_val; + ssn->client.last_pkt_ts = p->ts.tv_sec; + } + + SCLogDebug("ssn %p: Retransmitted SYN. Updated timestamp from packet %" PRIu64, ssn, + p->pcap_cnt); + } } /** \todo check if it's correct or set event */