netfilter: SYNPROXY: fix sending window update to client

Upon receipt of SYNACK from the server, ipt_SYNPROXY first sends back an ACK to
finish the server handshake, then calls nf_ct_seqadj_init() to initiate
sequence number adjustment of forwarded packets to the client and finally sends
a window update to the client to unblock it's TX queue.

Since synproxy_send_client_ack() does not set synproxy_send_tcp()'s nfct
parameter, no sequence number adjustment happens and the client receives the
window update with incorrect sequence number. Depending on client TCP
implementation, this leads to a significant delay (until a window probe is
being sent).

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c b/net/ipv4/netfilter/ipt_SYNPROXY.c
index fe8cc183411e..95ea633e8356 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -226,7 +226,8 @@ synproxy_send_client_ack(const struct synproxy_net *snet,
 
         synproxy_build_options(nth, opts);
 
-        synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
+        synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
+                          niph, nth, tcp_hdr_size);
 }
 
 static bool
diff --git a/net/ipv6/netfilter/ip6t_SYNPROXY.c b/net/ipv6/netfilter/ip6t_SYNPROXY.c
index bcebc24c6f0b..ebbb754c2111 100644
--- a/net/ipv6/netfilter/ip6t_SYNPROXY.c
+++ b/net/ipv6/netfilter/ip6t_SYNPROXY.c
@@ -243,7 +243,8 @@ synproxy_send_client_ack(const struct synproxy_net *snet,
 
         synproxy_build_options(nth, opts);
 
-        synproxy_send_tcp(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
+        synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
+                          niph, nth, tcp_hdr_size);
 }
 
 static bool