Add a reworked IPv4 options match - xt_ipv4options

This revision 1 of ipv4options makes it possible to match the
presence or absence of any of the 32 possible IP options, either all
or any of the options the user specified.

extensions/xt_ipv4options.c

@@ -0,0 +1,72 @@
+/*
+ *	xt_ipv4opts - Netfilter module to match IPv4 options
+ *	Copyright © Jan Engelhardt, 2009
+ *
+ *	This program is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU General Public License; either
+ *	version 2 of the License, or any later version, as published by the
+ *	Free Software Foundation.
+ */
+#include <linux/ip.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/netfilter/x_tables.h>
+#include <net/ip.h>
+#include "xt_ipv4options.h"
+#include "compat_xtables.h"
+
+static uint32_t ipv4options_rd(const uint8_t *data, int len)
+{
+	uint32_t opts = 0;
+
+	while (len >= 2) {
+		opts |= 1 << (data[0] & 0x1F);
+		len  -= data[1];
+		data += data[1];
+	}
+
+	return opts;
+}
+
+static bool ipv4options_mt(const struct sk_buff *skb,
+    const struct xt_match_param *par)
+{
+	const struct xt_ipv4options_mtinfo1 *info = par->matchinfo;
+	const struct iphdr *iph = ip_hdr(skb);
+	uint32_t opts = 0;
+	uint16_t len  = ip_hdrlen(skb) - sizeof(struct iphdr);
+
+	if (len > 0)
+		opts = ipv4options_rd((const void *)iph +
+		       sizeof(struct iphdr), len);
+
+	opts ^= info->invert;
+	opts &= info->map;
+	return (info->flags & XT_V4OPTS_ANY) ? opts : opts == info->map;
+}
+
+static struct xt_match ipv4options_mt_reg __read_mostly = {
+	.name      = "ipv4options",
+	.revision  = 1,
+	.family    = NFPROTO_IPV4,
+	.match     = ipv4options_mt,
+	.matchsize = XT_ALIGN(sizeof(struct xt_ipv4options_mtinfo1)),
+	.me        = THIS_MODULE,
+};
+
+static int __init ipv4options_mt_init(void)
+{
+	return xt_register_match(&ipv4options_mt_reg);
+}
+
+static void __exit ipv4options_mt_exit(void)
+{
+	xt_unregister_match(&ipv4options_mt_reg);
+}
+
+MODULE_DESCRIPTION("Xatblse: IPv4 option match");
+MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_ipv4options");
+module_init(ipv4options_mt_init);
+module_exit(ipv4options_mt_exit);