BUG/MINOR: quic: underflow issue for bbr_inflight_hi_from_lost_packet()

Add a test to ensure that values of a local variable used by
bbr_inflight_hi_from_lost_packet() is not be impacted by underflow issues
when subtracting too big numbers and make this function return a correct value.

Must be backported to 3.1.
This commit is contained in:
Frederic Lecaille 2024-12-12 12:04:14 +01:00
parent 22ab45a3a8
commit ebfc301d5d

View file

@ -1334,9 +1334,13 @@ static uint64_t bbr_inflight_hi_from_lost_packet(struct quic_cc_rs *rs,
BUG_ON(rs->lost < size);
/* What was lost before this packet? */
lost_prev = rs->lost - size;
if (BBR_LOSS_THRESH_MULT * inflight_prev < lost_prev * BBR_LOSS_THRESH_DIVI)
return inflight_prev;
lost_prefix =
(BBR_LOSS_THRESH_MULT * inflight_prev - lost_prev * BBR_LOSS_THRESH_DIVI) /
(BBR_LOSS_THRESH_DIVI - BBR_LOSS_THRESH_MULT);
/* At what inflight value did losses cross BBRLossThresh? */
return inflight_prev + lost_prefix;
}