src: introduce SYNPROXY matching

Add support for "synproxy" statement. For example (for TCP port 8888):

table ip x {
	chain y {
		type filter hook prerouting priority raw; policy accept;
		tcp dport 8888 tcp flags syn notrack
	}

	chain z {
		type filter hook input priority filter; policy accept;
		tcp dport 8888 ct state invalid,untracked synproxy mss 1460 wscale 7 timestamp sack-perm
		ct state invalid drop
	}
}

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 51 insertions, 0 deletions

diff --git a/src/statement.c b/src/statement.c
index a82c1b39..a9e72de3 100644
--- a/src/statement.c
+++ b/src/statement.c
@@ -29,6 +29,7 @@
 #include <netinet/in.h>
 #include <linux/netfilter/nf_nat.h>
 #include <linux/netfilter/nf_log.h>
+#include <linux/netfilter/nf_synproxy.h>
 
 struct stmt *stmt_alloc(const struct location *loc,
 			const struct stmt_ops *ops)
@@ -883,3 +884,53 @@ struct stmt *xt_stmt_alloc(const struct location *loc)
 {
 	return stmt_alloc(loc, &xt_stmt_ops);
 }
+
+static const char *synproxy_sack_to_str(const uint32_t flags)
+{
+	if (flags & NF_SYNPROXY_OPT_SACK_PERM)
+		return " sack-perm";
+
+	return "";
+}
+
+static const char *synproxy_timestamp_to_str(const uint32_t flags)
+{
+	if (flags & NF_SYNPROXY_OPT_TIMESTAMP)
+		return " timestamp";
+
+	return "";
+}
+
+static void synproxy_stmt_print(const struct stmt *stmt,
+				struct output_ctx *octx)
+{
+	uint32_t flags = stmt->synproxy.flags;
+	const char *ts_str = synproxy_timestamp_to_str(flags);
+	const char *sack_str = synproxy_sack_to_str(flags);
+
+	if (flags & (NF_SYNPROXY_OPT_MSS | NF_SYNPROXY_OPT_WSCALE))
+		nft_print(octx, "synproxy mss %u wscale %u%s%s",
+			  stmt->synproxy.mss, stmt->synproxy.wscale,
+			  ts_str, sack_str);
+	else if (flags & NF_SYNPROXY_OPT_MSS)
+		nft_print(octx, "synproxy mss %u%s%s", stmt->synproxy.mss,
+			  ts_str, sack_str);
+	else if (flags & NF_SYNPROXY_OPT_WSCALE)
+		nft_print(octx, "synproxy wscale %u%s%s", stmt->synproxy.wscale,
+			  ts_str, sack_str);
+	else
+		nft_print(octx, "synproxy%s%s", ts_str, sack_str);
+
+}
+
+static const struct stmt_ops synproxy_stmt_ops = {
+	.type		= STMT_SYNPROXY,
+	.name		= "synproxy",
+	.print		= synproxy_stmt_print,
+	.json		= synproxy_stmt_json,
+};
+
+struct stmt *synproxy_stmt_alloc(const struct location *loc)
+{
+	return stmt_alloc(loc, &synproxy_stmt_ops);
+}