path: root/net/ipv4/netfilter
diff options
authorJesper Dangaard Brouer <brouer@redhat.com>2013-08-28 15:14:38 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2013-09-04 11:43:11 +0200
commit775ada6d9f4c9dc440f5aeca00354eb87f6e0696 (patch)
tree2cd93057c6b969d68598e6a4d93b27c69c23c71c /net/ipv4/netfilter
parent5a17a390de7bdbcfff9b8f344273a886ca4cf8bf (diff)
netfilter: more strict TCP flag matching in SYNPROXY
Its seems Patrick missed to incoorporate some of my requested changes during review v2 of SYNPROXY netfilter module. Which were, to avoid SYN+ACK packets to enter the path, meant for the ACK packet from the client (from the 3WHS). Further there were a bug in ip6t_SYNPROXY.c, for matching SYN packets that didn't exclude the ACK flag. Go a step further with SYN packet/flag matching by excluding flags ACK+FIN+RST, in both IPv4 and IPv6 modules. The intented usage of SYNPROXY is as follows: (gracefully describing usage in commit) iptables -t raw -A PREROUTING -i eth0 -p tcp --dport 80 --syn -j NOTRACK iptables -A INPUT -i eth0 -p tcp --dport 80 -m state UNTRACKED,INVALID \ -j SYNPROXY --sack-perm --timestamp --mss 1480 --wscale 7 --ecn echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose This does filter SYN flags early, for packets in the UNTRACKED state, but packets in the INVALID state with other TCP flags could still reach the module, thus this stricter flag matching is still needed. Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Acked-by: Patrick McHardy <kaber@trash.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net/ipv4/netfilter')
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c b/net/ipv4/netfilter/ipt_SYNPROXY.c
index 94371db6aecc..90e489eb1c0a 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -269,7 +269,7 @@ synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
synproxy_parse_options(skb, par->thoff, th, &opts);
- if (th->syn && !th->ack) {
+ if (th->syn && !(th->ack || th->fin || th->rst)) {
/* Initial SYN from client */
@@ -285,7 +285,7 @@ synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
synproxy_send_client_synack(skb, th, &opts);
- } else if (th->ack && !(th->fin || th->rst))
+ } else if (th->ack && !(th->fin || th->rst || th->syn))
/* ACK from client */
synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));