tcp: detect SYN/data drop when F-RTO is disabled

On receiving the SYN-ACK, Fast Open checks icsk_retransmit for SYN
retransmission to detect SYN/data drops. But if F-RTO is disabled,
icsk_retransmit is reset at step D of tcp_fastretrans_alert() (
under tcp_ack()) before tcp_rcv_fastopen_synack(). The fix is to use
total_retrans instead which accounts for SYN retransmission regardless
the use of F-RTO.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 2 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 18f97ca76b00..8aca4ee95ff9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5649,8 +5649,7 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
          * the remote receives only the retransmitted (regular) SYNs: either
          * the original SYN-data or the corresponding SYN-ACK is lost.
          */
-        syn_drop = (cookie->len <= 0 && data &&
-                    inet_csk(sk)->icsk_retransmits);
+        syn_drop = (cookie->len <= 0 && data && tp->total_retrans);
 
         tcp_fastopen_cache_set(sk, mss, cookie, syn_drop);