[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: NHarald Welte <laforge@netfilter.org>
Signed-off-by: NArnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/dccp.h

@@ -242,10 +242,15 @@ static inline struct dccp_hdr_ext *dccp_hdrx(const struct sk_buff *skb)
 	return (struct dccp_hdr_ext *)(skb->h.raw + sizeof(struct dccp_hdr));
 }
 
+static inline unsigned int __dccp_basic_hdr_len(const struct dccp_hdr *dh)
+{
+	return sizeof(*dh) + (dh->dccph_x ? sizeof(struct dccp_hdr_ext) : 0);
+}
+
 static inline unsigned int dccp_basic_hdr_len(const struct sk_buff *skb)
 {
 	const struct dccp_hdr *dh = dccp_hdr(skb);
-	return sizeof(*dh) + (dh->dccph_x ? sizeof(struct dccp_hdr_ext) : 0);
+	return __dccp_basic_hdr_len(dh);
 }
 
 static inline __u64 dccp_hdr_seq(const struct sk_buff *skb)
@@ -297,10 +302,15 @@ static inline struct dccp_hdr_reset *dccp_hdr_reset(struct sk_buff *skb)
 	return (struct dccp_hdr_reset *)(skb->h.raw + dccp_basic_hdr_len(skb));
 }
 
+static inline unsigned int __dccp_hdr_len(const struct dccp_hdr *dh)
+{
+	return __dccp_basic_hdr_len(dh) +
+	       dccp_packet_hdr_len(dh->dccph_type);
+}
+
 static inline unsigned int dccp_hdr_len(const struct sk_buff *skb)
 {
-	return dccp_basic_hdr_len(skb) +
-	       dccp_packet_hdr_len(dccp_hdr(skb)->dccph_type);
+	return __dccp_hdr_len(dccp_hdr(skb));
 }
 
 

include/linux/netfilter_ipv4/ipt_dccp.h

+#ifndef _IPT_DCCP_H_
+#define _IPT_DCCP_H_
+
+#define IPT_DCCP_SRC_PORTS	        0x01
+#define IPT_DCCP_DEST_PORTS	        0x02
+#define IPT_DCCP_TYPE			0x04
+#define IPT_DCCP_OPTION			0x08
+
+#define IPT_DCCP_VALID_FLAGS		0x0f
+
+struct ipt_dccp_info {
+	u_int16_t dpts[2];  /* Min, Max */
+	u_int16_t spts[2];  /* Min, Max */
+
+	u_int16_t flags;
+	u_int16_t invflags;
+
+	u_int16_t typemask;
+	u_int8_t option;
+};
+
+#endif /* _IPT_DCCP_H_ */
+

net/ipv4/netfilter/Kconfig

@@ -354,6 +354,17 @@ config IP_NF_MATCH_SCTP
 	  If you want to compile it as a module, say M here and read
 	  <file:Documentation/modules.txt>.  If unsure, say `N'.
 
+config IP_NF_MATCH_DCCP
+	tristate  'DCCP protocol match support'
+	depends on IP_NF_IPTABLES
+	help
+	  With this option enabled, you will be able to use the iptables
+	  `dccp' match in order to match on DCCP source/destination ports
+	  and DCCP flags.
+
+	  If you want to compile it as a module, say M here and read
+	  <file:Documentation/modules.txt>.  If unsure, say `N'.
+
 config IP_NF_MATCH_COMMENT
 	tristate  'comment match support'
 	depends on IP_NF_IPTABLES

net/ipv4/netfilter/Makefile

@@ -42,6 +42,7 @@ obj-$(CONFIG_IP_NF_MATCH_HELPER) += ipt_helper.o
 obj-$(CONFIG_IP_NF_MATCH_LIMIT) += ipt_limit.o
 obj-$(CONFIG_IP_NF_MATCH_HASHLIMIT) += ipt_hashlimit.o
 obj-$(CONFIG_IP_NF_MATCH_SCTP) += ipt_sctp.o
+obj-$(CONFIG_IP_NF_MATCH_DCCP) += ipt_dccp.o
 obj-$(CONFIG_IP_NF_MATCH_MARK) += ipt_mark.o
 obj-$(CONFIG_IP_NF_MATCH_MAC) += ipt_mac.o
 obj-$(CONFIG_IP_NF_MATCH_IPRANGE) += ipt_iprange.o

net/ipv4/netfilter/ipt_dccp.c

+/*
+ * 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");
+