From: Frederic Lecaille <flecaille@haproxy.com>
Date: Thu, 28 May 2026 13:08:07 +0000 (+0200)
Subject: BUG/MEDIUM: quic: reset cwnd in slow_start on persistent congestion (cubic)
X-Git-Tag: v3.4.0~63
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=ab8603c6d5b035be89a0e9239d80221ec115380d;p=thirdparty%2Fhaproxy.git

BUG/MEDIUM: quic: reset cwnd in slow_start on persistent congestion (cubic)

The cubic slow_start callback was only resetting the internal cubic state
without reducing the congestion window, unlike newreno which calls
quic_cc_path_reset(). Per RFC 9002, persistent congestion should trigger
both entry into slow start and a reduction of the congestion window.

Must be backported to all versions.
---

diff --git a/src/quic_cc_cubic.c b/src/quic_cc_cubic.c
index 2532b54dc..98ba360b8 100644
--- a/src/quic_cc_cubic.c
+++ b/src/quic_cc_cubic.c
@@ -390,7 +390,10 @@ static inline void quic_cubic_update(struct quic_cc *cc, uint32_t acked)
 
 static void quic_cc_cubic_slow_start(struct quic_cc *cc)
 {
+	struct quic_cc_path *path = container_of(cc, struct quic_cc_path, cc);
+
 	TRACE_ENTER(QUIC_EV_CONN_CC, cc->qc);
+	quic_cc_path_reset(path);
 	quic_cc_cubic_reset(cc);
 	TRACE_LEAVE(QUIC_EV_CONN_CC, cc->qc);
 }