[TCP]: Wrap-safed reordering detection FRTO check

In case somebody has a suggestion about a better place for this
check, which must guarantee execution "early enough" (i.e,
before the wrap can occur), I'm very open to them.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c1339d88bbf3..7c1a92ffa083 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3027,6 +3027,9 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
         /* See if we can take anything off of the retransmit queue. */
         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
 
+        /* Guarantee sacktag reordering detection against wrap-arounds */
+        if (before(tp->frto_highmark, tp->snd_una))
+                tp->frto_highmark = 0;
         if (tp->frto_counter)
                 frto_cwnd = tcp_process_frto(sk, flag);