tcp: fix wraparound issue in tcp_lp

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>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index 046fd3910873..d6fb6c067af4 100644
--- 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, const struct ack_sample *sample)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct lp *lp = inet_csk_ca(sk);
+        u32 delta;
 
         if (sample->rtt_us > 0)
                 tcp_lp_rtt_sample(sk, sample->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))