lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 23 Nov 2020 13:21:42 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Ryan Sharpelletti <sharpelletti@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, Soheil Hassas Yeganeh <soheil@...gle.com>, Yuchung Cheng <ycheng@...gle.com>, Jakub Kicinski <kuba@...nel.org> Subject: [PATCH 4.19 22/91] tcp: only postpone PROBE_RTT if RTT is < current min_rtt estimate From: Ryan Sharpelletti <sharpelletti@...gle.com> [ Upstream commit 1b9e2a8c99a5c021041bfb2d512dc3ed92a94ffd ] During loss recovery, retransmitted packets are forced to use TCP timestamps to calculate the RTT samples, which have a millisecond granularity. BBR is designed using a microsecond granularity. As a result, multiple RTT samples could be truncated to the same RTT value during loss recovery. This is problematic, as BBR will not enter PROBE_RTT if the RTT sample is <= the current min_rtt sample, meaning that if there are persistent losses, PROBE_RTT will constantly be pushed off and potentially never re-entered. This patch makes sure that BBR enters PROBE_RTT by checking if RTT sample is < the current min_rtt sample, rather than <=. The Netflix transport/TCP team discovered this bug in the Linux TCP BBR code during lab tests. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Ryan Sharpelletti <sharpelletti@...gle.com> Signed-off-by: Neal Cardwell <ncardwell@...gle.com> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com> Signed-off-by: Yuchung Cheng <ycheng@...gle.com> Link: https://lore.kernel.org/r/20201116174412.1433277-1-sharpelletti.kdev@gmail.com Signed-off-by: Jakub Kicinski <kuba@...nel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- net/ipv4/tcp_bbr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -917,7 +917,7 @@ static void bbr_update_min_rtt(struct so filter_expired = after(tcp_jiffies32, bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); if (rs->rtt_us >= 0 && - (rs->rtt_us <= bbr->min_rtt_us || + (rs->rtt_us < bbr->min_rtt_us || (filter_expired && !rs->is_ack_delayed))) { bbr->min_rtt_us = rs->rtt_us; bbr->min_rtt_stamp = tcp_jiffies32;
Powered by blists - more mailing lists