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tcp: add tcp_syncookies mode to allow unconditionally generation of syncookies

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| 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>
This commit is contained in:
Hannes Frederic Sowa 2013-07-26 17:43:23 +02:00 committed by David S. Miller
parent dcfd8d5830
commit 5ad37d5dee
3 changed files with 9 additions and 3 deletions
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4
Documentation/networking/ip-sysctl.txt
View File

@ -440,6 +440,10 @@ tcp_syncookies - BOOLEAN
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

5
net/ipv4/tcp_ipv4.c
View File

@ -890,7 +890,7 @@ bool tcp_syn_flood_action(struct sock *sk,
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 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
* 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;

3
net/ipv6/tcp_ipv6.c
View File

@ -963,7 +963,8 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
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;