BUG/MINOR: quic: SIGFPE in quic_cubic_update()
As reported by @Tristan971 in GH #2116, the congestion control window could be zero
due to an inversion in the code about the reduction factor to be applied.
On a new loss event, it must be applied to the slow start threshold and the window
should never be below ->min_cwnd (2*max_udp_payload_sz).
Same issue in both newReno and cubic algorithm. Furthermore in newReno, only the
threshold was decremented.
Must be backported to 2.6 and 2.7.
diff --git a/src/quic_cc_cubic.c b/src/quic_cc_cubic.c
index d22897b..fd7fef5 100644
--- a/src/quic_cc_cubic.c
+++ b/src/quic_cc_cubic.c
@@ -197,8 +197,8 @@
else {
c->last_w_max = path->cwnd;
}
- path->cwnd = (CUBIC_BETA * path->cwnd) >> CUBIC_BETA_SCALE_SHIFT;
- c->ssthresh = QUIC_MAX(path->cwnd, path->min_cwnd);
+ c->ssthresh = (CUBIC_BETA * path->cwnd) >> CUBIC_BETA_SCALE_SHIFT;
+ path->cwnd = QUIC_MAX(c->ssthresh, (uint32_t)path->min_cwnd);
c->state = QUIC_CC_ST_RP;
TRACE_LEAVE(QUIC_EV_CONN_CC, cc->qc, NULL, cc);
}