RFC 5961 Section 5.2 / RFC 793 Section 3.9 require a challenge ACK
whenever an incoming SEG.ACK falls outside
[SND.UNA - MAX.SND.WND, SND.NXT]. There is currently no packetdrill
coverage for either edge.
Add tcp_rfc5961_ack-out-of-window.pkt, which in a single passive-open
connection exercises:
- Upper edge (SEG.ACK > SND.NXT): peer ACKs data that was never
sent before the server has transmitted anything.
- Lower edge (SEG.ACK < SND.UNA - MAX.SND.WND): after the server
has sent 2000 bytes (the peer-advertised rwnd forces two 1000-byte
segments, both acknowledged), peer sends an ACK that is older
than the acceptable window.
Both cases must elicit a challenge ACK
<SEQ = SND.NXT, ACK = RCV.NXT, CTL = ACK>. The per-socket RFC 5961
Section 7 rate limit is disabled for the duration of the test so that
both challenge ACKs can fire back-to-back.
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260422123605.320000-3-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Jiayuan Chen
cf94b3c0f0