[PATCH 3.16 106/134] tcp: fix wraparound issue in tcp_lp

Ben Hutchings
2017-08-18T13:15:52Z

From: Eric Dumazet <edumazet@google.com>

commit a9f11f963a546fea9144f6a6d1a307e814a387e7 upstream.

Be careful when comparing tcp_time_stamp to some u32 quantity,
otherwise result can be surprising.

Fixes: 7c106d7e782b ("[TCP]: TCP Low Priority congestion control")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/tcp_lp.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -264,13 +264,15 @@ static void tcp_lp_pkts_acked(struct soc
{
struct tcp_sock *tp = tcp_sk(sk);
struct lp *lp = inet_csk_ca(sk);
+ u32 delta;

if (rtt_us > 0)
tcp_lp_rtt_sample(sk, rtt_us);

/* calc inference */
- if (tcp_time_stamp > tp->rx_opt.rcv_tsecr)
- lp->inference = 3 * (tcp_time_stamp - tp->rx_opt.rcv_tsecr);
+ delta = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
+ if ((s32)delta > 0)
+ lp->inference = 3 * delta;

/* test if within inference */
if (lp->last_drop && (tcp_time_stamp - lp->last_drop < lp->inference))