1 files changed, 110 insertions, 0 deletions
diff --git a/net/netfilter/xt_tcpmss.c b/net/netfilter/xt_tcpmss.c
new file mode 100644
index 0000000..4809b34
--- /dev/null
+++ b/net/netfilter/xt_tcpmss.c
@@ -0,0 +1,110 @@
+/* Kernel module to match TCP MSS values. */
+
+/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
+ * Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <net/tcp.h>
+
+#include <linux/netfilter/xt_tcpmss.h>
+#include <linux/netfilter/x_tables.h>
+
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
+MODULE_DESCRIPTION("Xtables: TCP MSS match");
+MODULE_ALIAS("ipt_tcpmss");
+MODULE_ALIAS("ip6t_tcpmss");
+
+static bool
+tcpmss_mt(const struct sk_buff *skb, const struct xt_match_param *par)
+{
+	const struct xt_tcpmss_match_info *info = par->matchinfo;
+	const struct tcphdr *th;
+	struct tcphdr _tcph;
+	/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
+	const u_int8_t *op;
+	u8 _opt[15 * 4 - sizeof(_tcph)];
+	unsigned int i, optlen;
+
+	/* If we don't have the whole header, drop packet. */
+	th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
+	if (th == NULL)
+		goto dropit;
+
+	/* Malformed. */
+	if (th->doff*4 < sizeof(*th))
+		goto dropit;
+
+	optlen = th->doff*4 - sizeof(*th);
+	if (!optlen)
+		goto out;
+
+	/* Truncated options. */
+	op = skb_header_pointer(skb, par->thoff + sizeof(*th), optlen, _opt);
+	if (op == NULL)
+		goto dropit;
+
+	for (i = 0; i < optlen; ) {
+		if (op[i] == TCPOPT_MSS
+		    && (optlen - i) >= TCPOLEN_MSS
+		    && op[i+1] == TCPOLEN_MSS) {
+			u_int16_t mssval;
+
+			mssval = (op[i+2] << 8) | op[i+3];
+
+			return (mssval >= info->mss_min &&
+				mssval <= info->mss_max) ^ info->invert;
+		}
+		if (op[i] < 2)
+			i++;
+		else
+			i += op[i+1] ? : 1;
+	}
+out:
+	return info->invert;
+
+dropit:
+	*par->hotdrop = true;
+	return false;
+}
+
+static struct xt_match tcpmss_mt_reg[] __read_mostly = {
+	{
+		.name		= "tcpmss",
+		.family		= NFPROTO_IPV4,
+		.match		= tcpmss_mt,
+		.matchsize	= sizeof(struct xt_tcpmss_match_info),
+		.proto		= IPPROTO_TCP,
+		.me		= THIS_MODULE,
+	},
+	{
+		.name		= "tcpmss",
+		.family		= NFPROTO_IPV6,
+		.match		= tcpmss_mt,
+		.matchsize	= sizeof(struct xt_tcpmss_match_info),
+		.proto		= IPPROTO_TCP,
+		.me		= THIS_MODULE,
+	},
+};
+
+static int __init tcpmss_mt_init(void)
+{
+	return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
+}
+
+static void __exit tcpmss_mt_exit(void)
+{
+	xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
+}
+
+module_init(tcpmss_mt_init);
+module_exit(tcpmss_mt_exit);