[ 52/61] tcp: detect SYN/data drop when F-RTO is disabled

[Greg Kroah-Hartman]

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Yuchung Cheng <ycheng@xxxxxxxxxx>

[ Upstream commit 66555e92fb7a619188c02cceae4bbc414f15f96d ]

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@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/tcp_input.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5639,8 +5639,7 @@ static bool tcp_rcv_fastopen_synack(stru
 	 * 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);
 


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