/* Kernel module to match AH 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 <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_ah.h>

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("IPv6 AH match");
MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");

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

/* Returns 1 if the spi is matched by the range, 0 otherwise */
static inline int
spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, int invert)
{
	int r=0;
	DEBUGP("ah spi_match:%c 0x%x <= 0x%x <= 0x%x",invert? '!':' ',
	       min,spi,max);
	r = (spi >= min && spi <= max) ^ invert;
	DEBUGP(" result %s\n",r? "PASS\n" : "FAILED\n");
	return r;
}

static int
match(const struct sk_buff *skb,
      const struct net_device *in,
      const struct net_device *out,
      const void *matchinfo,
      int offset,
      unsigned int protoff,
      int *hotdrop)
{
	struct ip_auth_hdr *ah = NULL, _ah;
	const struct ip6t_ah *ahinfo = matchinfo;
	unsigned int temp;
	int len;
	u8 nexthdr;
	unsigned int ptr;
	unsigned int hdrlen = 0;

	/*DEBUGP("IPv6 AH entered\n");*/
	/* if (opt->auth == 0) return 0;
	* It does not filled on output */

	/* type of the 1st exthdr */
	nexthdr = skb->nh.ipv6h->nexthdr;
	/* pointer to the 1st exthdr */
	ptr = sizeof(struct ipv6hdr);
	/* available length */
	len = skb->len - ptr;
	temp = 0;

	while (ip6t_ext_hdr(nexthdr)) {
		struct ipv6_opt_hdr _hdr, *hp;

		DEBUGP("ipv6_ah header iteration \n");

		/* Is there enough space for the next ext header? */
		if (len < sizeof(struct ipv6_opt_hdr))
			return 0;
		/* No more exthdr -> evaluate */
		if (nexthdr == NEXTHDR_NONE)
			break;
		/* ESP -> evaluate */
		if (nexthdr == NEXTHDR_ESP)
			break;

		hp = skb_header_pointer(skb, ptr, sizeof(_hdr), &_hdr);
		BUG_ON(hp == NULL);

		/* Calculate the header length */
		if (nexthdr == NEXTHDR_FRAGMENT)
			hdrlen = 8;
		else if (nexthdr == NEXTHDR_AUTH)
			hdrlen = (hp->hdrlen+2)<<2;
		else
			hdrlen = ipv6_optlen(hp);

		/* AH -> evaluate */
		if (nexthdr == NEXTHDR_AUTH) {
			temp |= MASK_AH;
			break;
		}

		
		/* set the flag */
		switch (nexthdr) {
		case NEXTHDR_HOP:
		case NEXTHDR_ROUTING:
		case NEXTHDR_FRAGMENT:
		case NEXTHDR_AUTH:
		case NEXTHDR_DEST:
			break;
		default:
			DEBUGP("ipv6_ah match: unknown nextheader %u\n",nexthdr);
			return 0;
		}

		nexthdr = hp->nexthdr;
		len -= hdrlen;
		ptr += hdrlen;
		if (ptr > skb->len) {
			DEBUGP("ipv6_ah: new pointer too large! \n");
			break;
		}
	}

	/* AH header not found */
	if (temp != MASK_AH)
		return 0;

	if (len < sizeof(struct ip_auth_hdr)){
		*hotdrop = 1;
		return 0;
	}

	ah = skb_header_pointer(skb, ptr, sizeof(_ah), &_ah);
	BUG_ON(ah == NULL);

	DEBUGP("IPv6 AH LEN %u %u ", hdrlen, ah->hdrlen);
	DEBUGP("RES %04X ", ah->reserved);
	DEBUGP("SPI %u %08X\n", ntohl(ah->spi), ntohl(ah->spi));

	DEBUGP("IPv6 AH spi %02X ",
	       (spi_match(ahinfo->spis[0], ahinfo->spis[1],
	                  ntohl(ah->spi),
	                  !!(ahinfo->invflags & IP6T_AH_INV_SPI))));
	DEBUGP("len %02X %04X %02X ",
	       ahinfo->hdrlen, hdrlen,
	       (!ahinfo->hdrlen ||
	        (ahinfo->hdrlen == hdrlen) ^
	        !!(ahinfo->invflags & IP6T_AH_INV_LEN)));
	DEBUGP("res %02X %04X %02X\n",
	       ahinfo->hdrres, ah->reserved,
	       !(ahinfo->hdrres && ah->reserved));

	return (ah != NULL)
	       &&
	       (spi_match(ahinfo->spis[0], ahinfo->spis[1],
	                  ntohl(ah->spi),
	                  !!(ahinfo->invflags & IP6T_AH_INV_SPI)))
	       &&
	       (!ahinfo->hdrlen ||
	        (ahinfo->hdrlen == hdrlen) ^
	        !!(ahinfo->invflags & IP6T_AH_INV_LEN))
	       &&
	       !(ahinfo->hdrres && ah->reserved);
}

/* Called when user tries to insert an entry of this type. */
static int
checkentry(const char *tablename,
          const struct ip6t_ip6 *ip,
          void *matchinfo,
          unsigned int matchinfosize,
          unsigned int hook_mask)
{
	const struct ip6t_ah *ahinfo = matchinfo;

	if (matchinfosize != IP6T_ALIGN(sizeof(struct ip6t_ah))) {
		DEBUGP("ip6t_ah: matchsize %u != %u\n",
		       matchinfosize, IP6T_ALIGN(sizeof(struct ip6t_ah)));
		return 0;
	}
	if (ahinfo->invflags & ~IP6T_AH_INV_MASK) {
		DEBUGP("ip6t_ah: unknown flags %X\n", ahinfo->invflags);
		return 0;
	}
	return 1;
}

static struct ip6t_match ah_match = {
	.name		= "ah",
	.match		= &match,
	.checkentry	= &checkentry,
	.me		= THIS_MODULE,
};

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

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

module_init(init);
module_exit(cleanup);