tcp: add tcp_syncookies mode to allow unconditionally generation of syncookies
| If you want to test which effects syncookies have to your
| network connections you can set this knob to 2 to enable
| unconditionally generation of syncookies.
Original idea and first implementation by Eric Dumazet.
Cc: Florian Westphal <fw@strlen.de>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 53cea9b..36be26b 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -440,6 +440,10 @@
SYN flood warnings in logs not being really flooded, your server
is seriously misconfigured.
+ If you want to test which effects syncookies have to your
+ network connections you can set this knob to 2 to enable
+ unconditionally generation of syncookies.
+
tcp_fastopen - INTEGER
Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
in the opening SYN packet. To use this feature, the client application
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2a5d5c4..280efe5 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -890,7 +890,7 @@
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
lopt = inet_csk(sk)->icsk_accept_queue.listen_opt;
- if (!lopt->synflood_warned) {
+ if (!lopt->synflood_warned && sysctl_tcp_syncookies != 2) {
lopt->synflood_warned = 1;
pr_info("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
proto, ntohs(tcp_hdr(skb)->dest), msg);
@@ -1462,7 +1462,8 @@
* limitations, they conserve resources and peer is
* evidently real one.
*/
- if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
+ if ((sysctl_tcp_syncookies == 2 ||
+ inet_csk_reqsk_queue_is_full(sk)) && !isn) {
want_cookie = tcp_syn_flood_action(sk, skb, "TCP");
if (!want_cookie)
goto drop;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index b792e87..38c196c 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -963,7 +963,8 @@
if (!ipv6_unicast_destination(skb))
goto drop;
- if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
+ if ((sysctl_tcp_syncookies == 2 ||
+ inet_csk_reqsk_queue_is_full(sk)) && !isn) {
want_cookie = tcp_syn_flood_action(sk, skb, "TCPv6");
if (!want_cookie)
goto drop;