Add iptables support for the TPROXY target

new file mode 100644
index 0000000..0f910f4
@@ -0,0 +1,151 @@
+/*
+ * Shared library add-on to iptables to add TPROXY target support.
+ *
+ * Copyright (C) 2002-2008 BalaBit IT Ltd.
+ */
+#include <getopt.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <limits.h>
+
+#include <iptables.h>
+#include <xtables.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_TPROXY.h>
+
+static const struct option tproxy_tg_opts[] = {
+	{ .name = "on-port", .has_arg = 1, .val = '1'},
+	{ .name = "on-ip", .has_arg = 1, .val = '2'},
+	{ .name = "tproxy-mark", .has_arg = 1, .val = '3'},
+	{NULL},
+};
+
+enum {
+	PARAM_ONPORT = 1 << 0,
+	PARAM_ONIP = 1 << 1,
+	PARAM_MARK = 1 << 2,
+};
+
+static void tproxy_tg_help(void)
+{
+	printf(
+"TPROXY target options:\n"
+"  --on-port port		    Redirect connection to port, or the original port if 0\n"
+"  --on-ip ip			    Optionally redirect to the given IP\n"
+"  --tproxy-mark value[/mask]	    Mark packets with the given value/mask\n\n");
+}
+
+static void parse_tproxy_lport(const char *s, struct xt_tproxy_target_info *info)
+{
+	unsigned int lport;
+
+	if (string_to_number(s, 0, 65535, &lport) != -1)
+		info->lport = htons(lport);
+	else
+		param_act(P_BAD_VALUE, "TPROXY", "--on-port", s);
+}
+
+static void parse_tproxy_laddr(const char *s, struct xt_tproxy_target_info *info)
+{
+	struct in_addr *laddr;
+
+	if ((laddr = numeric_to_ipaddr(s)) == NULL)
+		param_act(P_BAD_VALUE, "TPROXY", "--on-ip", s);
+
+	info->laddr = laddr->s_addr;
+}
+
+static void parse_tproxy_mark(char *s, struct xt_tproxy_target_info *info)
+{
+	unsigned int value, mask = ~0U;
+	char *end;
+
+	if (!strtonum(s, &end, &value, 0, UINT_MAX))
+		param_act(P_BAD_VALUE, "TPROXY", "--tproxy-mark", s);
+	if (*end == '/')
+		if (!strtonum(end + 1, &end, &mask, 0, UINT_MAX))
+			param_act(P_BAD_VALUE, "TPROXY", "--tproxy-mark", s);
+	if (*end != '\0')
+		param_act(P_BAD_VALUE, "TPROXY", "--tproxy-mark", s);
+
+	info->mark_mask = mask;
+	info->mark_value = value;
+}
+
+static int tproxy_tg_parse(int c, char **argv, int invert, unsigned int *flags,
+			const void *entry, struct xt_entry_target **target)
+{
+	struct xt_tproxy_target_info *tproxyinfo = (void *)(*target)->data;
+
+	switch (c) {
+	case '1':
+		param_act(P_ONLY_ONCE, "TPROXY", "--on-port", *flags & PARAM_ONPORT);
+		param_act(P_NO_INVERT, "TPROXY", "--on-port", invert);
+		parse_tproxy_lport(optarg, tproxyinfo);
+		*flags |= PARAM_ONPORT;
+		return 1;
+	case '2':
+		param_act(P_ONLY_ONCE, "TPROXY", "--on-ip", *flags & PARAM_ONIP);
+		param_act(P_NO_INVERT, "TPROXY", "--on-ip", invert);
+		parse_tproxy_laddr(optarg, tproxyinfo);
+		*flags |= PARAM_ONIP;
+		return 1;
+	case '3':
+		param_act(P_ONLY_ONCE, "TPROXY", "--tproxy-mark", *flags & PARAM_MARK);
+		param_act(P_NO_INVERT, "TPROXY", "--tproxy-mark", invert);
+		parse_tproxy_mark(optarg, tproxyinfo);
+		*flags |= PARAM_MARK;
+		return 1;
+	}
+
+	return 0;
+}
+
+static void tproxy_tg_check(unsigned int flags)
+{
+	if (!(flags & PARAM_ONPORT))
+		exit_error(PARAMETER_PROBLEM,
+			   "TPROXY target: Parameter --on-port is required");
+}
+
+static void tproxy_tg_print(const void *ip, const struct xt_entry_target *target,
+			 int numeric)
+{
+	const struct xt_tproxy_target_info *info = (const void *)target->data;
+	printf("TPROXY redirect %s:%u mark 0x%x/0x%x",
+	       ipaddr_to_numeric((const struct in_addr *)&info->laddr),
+	       ntohs(info->lport), (unsigned int)info->mark_value,
+	       (unsigned int)info->mark_mask);
+}
+
+static void tproxy_tg_save(const void *ip, const struct xt_entry_target *target)
+{
+	const struct xt_tproxy_target_info *info = (const void *)target->data;
+
+	printf("--on-port %u ", ntohs(info->lport));
+	printf("--on-ip %s ",
+	       ipaddr_to_numeric((const struct in_addr *)&info->laddr));
+	printf("--tproxy-mark 0x%x/0x%x ",
+	       (unsigned int)info->mark_value, (unsigned int)info->mark_mask);
+}
+
+static struct xtables_target tproxy_tg_reg = {
+	.name	       = "TPROXY",
+	.family	       = AF_INET,
+	.version       = XTABLES_VERSION,
+	.size	       = XT_ALIGN(sizeof(struct xt_tproxy_target_info)),
+	.userspacesize = XT_ALIGN(sizeof(struct xt_tproxy_target_info)),
+	.help	       = tproxy_tg_help,
+	.parse	       = tproxy_tg_parse,
+	.final_check   = tproxy_tg_check,
+	.print	       = tproxy_tg_print,
+	.save	       = tproxy_tg_save,
+	.extra_opts    = tproxy_tg_opts,
+};
+
+void _init(void)
+{
+	xtables_register_target(&tproxy_tg_reg);
+}

new file mode 100644
index 0000000..152e8f9
@@ -0,0 +1,14 @@
+#ifndef _XT_TPROXY_H_target
+#define _XT_TPROXY_H_target
+
+/* TPROXY target is capable of marking the packet to perform
+ * redirection. We can get rid of that whenever we get support for
+ * mutliple targets in the same rule. */
+struct xt_tproxy_target_info {
+	u_int32_t mark_mask;
+	u_int32_t mark_value;
+	__be32 laddr;
+	__be16 lport;
+};
+
+#endif /* _XT_TPROXY_H_target */