linux-2.6.34.13/net/ipv4/tcp_ipv4.c

gistfile1.txt

1362         else if (!sysctl_tcp_syncookies &&
1363              (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
1364               (sysctl_max_syn_backlog >> 2)) &&
1365              (!peer || !peer->tcp_ts_stamp) &&
1366              (!dst || !dst_metric(dst, RTAX_RTT))) {
1367             /* Without syncookies last quarter of
1368              * backlog is filled with destinations,
1369              * proven to be alive.
1370              * It means that we continue to communicate
1371              * to destinations, already remembered
1372              * to the moment of synflood.
1373              */
1374             LIMIT_NETDEBUG(KERN_DEBUG "TCP: drop open request from %pI4/%u\n",
1375                        &saddr, ntohs(tcp_hdr(skb)->source));
1376             goto drop_and_release;
1377         }