On Mon, Feb 03, 2025 at 08:25:58AM +0100, Stefano Brivio wrote:Reported by somebody on IRC: if the server has considerable latency, it might happen that the client retries sending SYN segments for the same flow while we're still in a TAP_SYN_RCVD, non-ESTABLISHED state. In that case, we should go with the blanket assumption that we need to reset the connection on any unexpected segment: RFC 9293 explicitly mentions this case in Figure 8: Recovery from Old Duplicate SYN, section 3.5. It doesn't make sense for us to set a specific sequence number, socket-side, but we should definitely wait and see. Ignoring the duplicate SYN segment should also be compatible with section 3.10.7.3. SYN-SENT STATE, which mentions updating sequences socket-side (which we can't do anyway), but certainly not reset the connection. Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>I haven't dug into the RFC to check this thoroughly, but it makes intuitive sense to me. Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>--- tcp.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tcp.c b/tcp.c index 7787381..51ad692 100644 --- a/tcp.c +++ b/tcp.c @@ -1920,6 +1920,9 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, /* Establishing connection from tap */ if (conn->events & TAP_SYN_RCVD) { + if (th->syn && !th->ack && !th->fin) + return 1; /* SYN retry: ignore and keep waiting */ + if (!(conn->events & TAP_SYN_ACK_SENT)) goto reset;-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson