From 45eb7e48817f0435040c3efc15e66383d78ed71f Mon Sep 17 00:00:00 2001 From: Victor Julien Date: Fri, 20 Sep 2024 09:54:57 +0200 Subject: [PATCH] stream: improve 3whs completed by ACK with data If the ACK packet completing the 3whs is received, the stream engine will transition to "established". However, the packet itself will not be tagged as "established". This will only happen for the next packet after the 3whs, so that `flow:established` only matches after the 3whs. It is possible that the ACK packet completing the 3whs was lost. Since the ACK packets themselves are not acknowledged, there will be no retransmission of them. Instead, the next packet can have the expected ACK flag as well as data. This case was mishandled in a subtle way. The stream engine state transition was done correctly, as well as the data handling and app-layer updates. However, the packet itself was not tagged as "established", which meant that `flow:established` would not yet match. This patch detects this case and tags the packet as established if ACK with data is received that completes the 3whs. Bug: #7264. --- src/stream-tcp.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/src/stream-tcp.c b/src/stream-tcp.c index b212f1e99164..1ae7c013ae12 100644 --- a/src/stream-tcp.c +++ b/src/stream-tcp.c @@ -2520,6 +2520,14 @@ static int StreamTcpPacketStateSynRecv( StreamTcpPacketSetState(p, ssn, TCP_ESTABLISHED); SCLogDebug("ssn %p: =~ ssn state is now TCP_ESTABLISHED", ssn); + /* special case: normally the packet following the 3whs is + * considered flow established, but with data we need it to + * be established now. This can happen if the original ACK was + * lost. */ + if (p->payload_len) { + p->flowflags |= FLOW_PKT_ESTABLISHED; + } + StreamTcpReassembleHandleSegment(tv, stt->ra_ctx, ssn, &ssn->client, p); /* If asynchronous stream handling is allowed then set the session,