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

From: Greg Kroah-Hartman
Date: Tue Feb 12 2013 - 15:57:59 EST

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);

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/