ip6t_hbh.c

/* Kernel module to match Hop-by-Hop and Destination parameters. */

/* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
 *
 * 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/ipv6.h>
#include <linux/types.h>
#include <net/checksum.h>
#include <net/ipv6.h>

#include <asm/byteorder.h>

#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_opts.h>

#define HOPBYHOP	1

MODULE_LICENSE("GPL");
#if HOPBYHOP
MODULE_DESCRIPTION("IPv6 HbH match");
#else
MODULE_DESCRIPTION("IPv6 DST match");
#endif
MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");

#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif

/*
 *  (Type & 0xC0) >> 6
 *	0	-> ignorable
 *	1	-> must drop the packet
 *	2	-> send ICMP PARM PROB regardless and drop packet
 *	3	-> Send ICMP if not a multicast address and drop packet
 *  (Type & 0x20) >> 5
 *	0	-> invariant
 *	1	-> can change the routing
 *  (Type & 0x1F) Type
 *	0	-> Pad1 (only 1 byte!)
 *	1	-> PadN LENGTH info (total length = length + 2)
 *	C0 | 2	-> JUMBO 4 x x x x ( xxxx > 64k )
 *	5	-> RTALERT 2 x x
 */

static int
match(const struct sk_buff *skb,
      const struct net_device *in,
      const struct net_device *out,
      const struct xt_match *match,
      const void *matchinfo,
      int offset,
      unsigned int protoff,
      int *hotdrop)
{
	struct ipv6_opt_hdr _optsh, *oh;
	const struct ip6t_opts *optinfo = matchinfo;
	unsigned int temp;
	unsigned int ptr;
	unsigned int hdrlen = 0;
	unsigned int ret = 0;
	u8 _opttype, *tp = NULL;
	u8 _optlen, *lp = NULL;
	unsigned int optlen;

#if HOPBYHOP
	if (ipv6_find_hdr(skb, &ptr, NEXTHDR_HOP, NULL) < 0)
#else
	if (ipv6_find_hdr(skb, &ptr, NEXTHDR_DEST, NULL) < 0)
#endif
		return 0;

	oh = skb_header_pointer(skb, ptr, sizeof(_optsh), &_optsh);
	if (oh == NULL) {
		*hotdrop = 1;
		return 0;
	}

	hdrlen = ipv6_optlen(oh);
	if (skb->len - ptr < hdrlen) {
		/* Packet smaller than it's length field */
		return 0;
	}

	DEBUGP("IPv6 OPTS LEN %u %u ", hdrlen, oh->hdrlen);

	DEBUGP("len %02X %04X %02X ",
	       optinfo->hdrlen, hdrlen,
	       (!(optinfo->flags & IP6T_OPTS_LEN) ||
		((optinfo->hdrlen == hdrlen) ^
		 !!(optinfo->invflags & IP6T_OPTS_INV_LEN))));

	ret = (oh != NULL) &&
	      (!(optinfo->flags & IP6T_OPTS_LEN) ||
	       ((optinfo->hdrlen == hdrlen) ^
		!!(optinfo->invflags & IP6T_OPTS_INV_LEN)));

	ptr += 2;
	hdrlen -= 2;
	if (!(optinfo->flags & IP6T_OPTS_OPTS)) {
		return ret;
	} else if (optinfo->flags & IP6T_OPTS_NSTRICT) {
		DEBUGP("Not strict - not implemented");
	} else {
		DEBUGP("Strict ");
		DEBUGP("#%d ", optinfo->optsnr);
		for (temp = 0; temp < optinfo->optsnr; temp++) {
			/* type field exists ? */
			if (hdrlen < 1)
				break;
			tp = skb_header_pointer(skb, ptr, sizeof(_opttype),
						&_opttype);
			if (tp == NULL)
				break;

			/* Type check */
			if (*tp != (optinfo->opts[temp] & 0xFF00) >> 8) {
				DEBUGP("Tbad %02X %02X\n",
				       *tp,
				       (optinfo->opts[temp] & 0xFF00) >> 8);
				return 0;
			} else {
				DEBUGP("Tok ");
			}
			/* Length check */
			if (*tp) {
				u16 spec_len;

				/* length field exists ? */
				if (hdrlen < 2)
					break;
				lp = skb_header_pointer(skb, ptr + 1,
							sizeof(_optlen),
							&_optlen);
				if (lp == NULL)
					break;
				spec_len = optinfo->opts[temp] & 0x00FF;

				if (spec_len != 0x00FF && spec_len != *lp) {
					DEBUGP("Lbad %02X %04X\n", *lp,
					       spec_len);
					return 0;
				}
				DEBUGP("Lok ");
				optlen = *lp + 2;
			} else {
				DEBUGP("Pad1\n");
				optlen = 1;
			}

			/* Step to the next */
			DEBUGP("len%04X \n", optlen);

			if ((ptr > skb->len - optlen || hdrlen < optlen) &&
			    (temp < optinfo->optsnr - 1)) {
				DEBUGP("new pointer is too large! \n");
				break;
			}
			ptr += optlen;
			hdrlen -= optlen;
		}
		if (temp == optinfo->optsnr)
			return ret;
		else
			return 0;
	}

	return 0;
}

/* Called when user tries to insert an entry of this type. */
static int
checkentry(const char *tablename,
	   const void *entry,
	   const struct xt_match *match,
	   void *matchinfo,
	   unsigned int matchinfosize,
	   unsigned int hook_mask)
{
	const struct ip6t_opts *optsinfo = matchinfo;

	if (optsinfo->invflags & ~IP6T_OPTS_INV_MASK) {
		DEBUGP("ip6t_opts: unknown flags %X\n", optsinfo->invflags);
		return 0;
	}
	return 1;
}

static struct ip6t_match opts_match = {
#if HOPBYHOP
	.name		= "hbh",
#else
	.name		= "dst",
#endif
	.match		= match,
	.matchsize	= sizeof(struct ip6t_opts),
	.checkentry	= checkentry,
	.me		= THIS_MODULE,
};

static int __init init(void)
{
	return ip6t_register_match(&opts_match);
}

static void __exit cleanup(void)
{
	ip6t_unregister_match(&opts_match);
}

module_init(init);
module_exit(cleanup);