netfilter: ctnetlink: synproxy support

This patch exposes synproxy information per-conntrack. Moreover, send
sequence adjustment events once server sends us the SYN,ACK packet, so
we can synchronize the sequence adjustment too for packets going as
reply from the server, as part of the synproxy logic.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_conntrack_common.h

@@ -129,6 +129,7 @@ enum ip_conntrack_events {
 	IPCT_NATSEQADJ = IPCT_SEQADJ,
 	IPCT_SECMARK,		/* new security mark has been set */
 	IPCT_LABEL,		/* new connlabel has been set */
+	IPCT_SYNPROXY,		/* synproxy has been set */
 #ifdef __KERNEL__
 	__IPCT_MAX
 #endif

include/uapi/linux/netfilter/nfnetlink_conntrack.h

@@ -54,6 +54,7 @@ enum ctattr_type {
 	CTA_MARK_MASK,
 	CTA_LABELS,
 	CTA_LABELS_MASK,
+	CTA_SYNPROXY,
 	__CTA_MAX
 };
 #define CTA_MAX (__CTA_MAX - 1)
@@ -190,6 +191,15 @@ enum ctattr_natseq {
 };
 #define CTA_NAT_SEQ_MAX (__CTA_NAT_SEQ_MAX - 1)
 
+enum ctattr_synproxy {
+	CTA_SYNPROXY_UNSPEC,
+	CTA_SYNPROXY_ISN,
+	CTA_SYNPROXY_ITS,
+	CTA_SYNPROXY_TSOFF,
+	__CTA_SYNPROXY_MAX,
+};
+#define CTA_SYNPROXY_MAX (__CTA_SYNPROXY_MAX - 1)
+
 enum ctattr_expect {
 	CTA_EXPECT_UNSPEC,
 	CTA_EXPECT_MASTER,