tcp: fix wraparound issue in tcp_lp

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 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index 72f7218..8d24d0b 100644 (file)
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -264,13 +264,15 @@ static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, s32 rtt_us)
 {
        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))