[NETFILTER]: New iptables DCCP protocol header match

Using this new iptables DCCP protocol header match, it is possible to
create simplistic stateless packet filtering rules for DCCP.  It
permits matching of port numbers, packet type and options.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 176 insertions, 0 deletions

diff --git a/net/ipv4/netfilter/ipt_dccp.c b/net/ipv4/netfilter/ipt_dccp.c
new file mode 100644
index 000000000000..ad3278bba6c1
--- /dev/null
+++ b/net/ipv4/netfilter/ipt_dccp.c
@@ -0,0 +1,176 @@
+/*
+ * iptables module for DCCP protocol header matching
+ *
+ * (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 <linux/spinlock.h>
+#include <net/ip.h>
+#include <linux/dccp.h>
+
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv4/ipt_dccp.h>
+
+#define DCCHECK(cond, option, flag, invflag) (!((flag) & (option)) \
+		                  || (!!((invflag) & (option)) ^ (cond)))
+
+static unsigned char *dccp_optbuf;
+static DEFINE_SPINLOCK(dccp_buflock);
+
+static inline int
+dccp_find_option(u_int8_t option,
+		 const struct sk_buff *skb,
+		 const struct dccp_hdr *dh,
+		 int *hotdrop)
+{
+	/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
+	unsigned char *op;
+	unsigned int optoff = __dccp_hdr_len(dh);
+	unsigned int optlen = dh->dccph_doff*4 - __dccp_hdr_len(dh);
+	unsigned int i;
+
+	if (dh->dccph_doff * 4 < __dccp_hdr_len(dh)) {
+		*hotdrop = 1;
+		return 0;
+	}
+
+	if (!optlen)
+		return 0;
+
+	spin_lock_bh(&dccp_buflock);
+	op = skb_header_pointer(skb,
+				skb->nh.iph->ihl*4 + optoff,
+				optlen, dccp_optbuf);
+	if (op == NULL) {
+		/* If we don't have the whole header, drop packet. */
+		spin_unlock_bh(&dccp_buflock);
+		*hotdrop = 1;
+		return 0;
+	}
+
+	for (i = 0; i < optlen; ) {
+		if (op[i] == option) {
+			spin_unlock_bh(&dccp_buflock);
+			return 1;
+		}
+
+		if (op[i] < 2) 
+			i++;
+		else 
+			i += op[i+1]?:1;
+	}
+
+	spin_unlock_bh(&dccp_buflock);
+	return 0;
+}
+
+
+static inline int
+match_types(const struct dccp_hdr *dh, u_int16_t typemask)
+{
+	return (typemask & (1 << dh->dccph_type));
+}
+
+static inline int
+match_option(u_int8_t option, const struct sk_buff *skb,
+	     const struct dccp_hdr *dh, int *hotdrop)
+{
+	return dccp_find_option(option, skb, dh, hotdrop);
+}
+
+static int
+match(const struct sk_buff *skb,
+      const struct net_device *in,
+      const struct net_device *out,
+      const void *matchinfo,
+      int offset,
+      int *hotdrop)
+{
+	const struct ipt_dccp_info *info = 
+				(const struct ipt_dccp_info *)matchinfo;
+	struct dccp_hdr _dh, *dh;
+
+	if (offset)
+		return 0;
+	
+	dh = skb_header_pointer(skb, skb->nh.iph->ihl*4, sizeof(_dh), &_dh);
+	if (dh == NULL) {
+		*hotdrop = 1;
+		return 0;
+       	}
+
+	return  DCCHECK(((ntohs(dh->dccph_sport) >= info->spts[0]) 
+			&& (ntohs(dh->dccph_sport) <= info->spts[1])), 
+		   	IPT_DCCP_SRC_PORTS, info->flags, info->invflags)
+		&& DCCHECK(((ntohs(dh->dccph_dport) >= info->dpts[0]) 
+			&& (ntohs(dh->dccph_dport) <= info->dpts[1])), 
+			IPT_DCCP_DEST_PORTS, info->flags, info->invflags)
+		&& DCCHECK(match_types(dh, info->typemask),
+			   IPT_DCCP_TYPE, info->flags, info->invflags)
+		&& DCCHECK(match_option(info->option, skb, dh, hotdrop),
+			   IPT_DCCP_OPTION, info->flags, info->invflags);
+}
+
+static int
+checkentry(const char *tablename,
+	   const struct ipt_ip *ip,
+	   void *matchinfo,
+	   unsigned int matchsize,
+	   unsigned int hook_mask)
+{
+	const struct ipt_dccp_info *info;
+
+	info = (const struct ipt_dccp_info *)matchinfo;
+
+	return ip->proto == IPPROTO_DCCP
+		&& !(ip->invflags & IPT_INV_PROTO)
+		&& matchsize == IPT_ALIGN(sizeof(struct ipt_dccp_info))
+		&& !(info->flags & ~IPT_DCCP_VALID_FLAGS)
+		&& !(info->invflags & ~IPT_DCCP_VALID_FLAGS)
+		&& !(info->invflags & ~info->flags);
+}
+
+static struct ipt_match dccp_match = 
+{ 
+	.name 		= "dccp",
+	.match		= &match,
+	.checkentry	= &checkentry,
+	.me 		= THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	int ret;
+
+	/* doff is 8 bits, so the maximum option size is (4*256).  Don't put
+	 * this in BSS since DaveM is worried about locked TLB's for kernel
+	 * BSS. */
+	dccp_optbuf = kmalloc(256 * 4, GFP_KERNEL);
+	if (!dccp_optbuf)
+		return -ENOMEM;
+	ret = ipt_register_match(&dccp_match);
+	if (ret)
+		kfree(dccp_optbuf);
+
+	return ret;
+}
+
+static void __exit fini(void)
+{
+	ipt_unregister_match(&dccp_match);
+	kfree(dccp_optbuf);
+}
+
+module_init(init);
+module_exit(fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
+MODULE_DESCRIPTION("Match for DCCP protocol packets");
+