// SPDX-License-Identifier: GPL-2.0-only
/* ipv6header match - matches IPv6 packets based
   on whether they contain certain headers */

/* Original idea: Brad Chapman
 * Rewritten by: Andras Kis-Szabo <kisza@sch.bme.hu> */

/* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
 */

#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/x_tables.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_ipv6/ip6t_ipv6header.h>

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

static bool
ipv6header_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
        const struct ip6t_ipv6header_info *info = par->matchinfo;
        unsigned int temp;
        int len;
        u8 nexthdr;
        unsigned int ptr;

        /* Make sure this isn't an evil packet */

        /* type of the 1st exthdr */
        nexthdr = ipv6_hdr(skb)->nexthdr;
        /* pointer to the 1st exthdr */
        ptr = sizeof(struct ipv6hdr);
        /* available length */
        len = skb->len - ptr;
        temp = 0;

        while (nf_ip6_ext_hdr(nexthdr)) {
                const struct ipv6_opt_hdr *hp;
                struct ipv6_opt_hdr _hdr;
                int hdrlen;

                /* No more exthdr -> evaluate */
                if (nexthdr == NEXTHDR_NONE) {
                        temp |= MASK_NONE;
                        break;
                }
                /* Is there enough space for the next ext header? */
                if (len < (int)sizeof(struct ipv6_opt_hdr))
                        return false;
                /* ESP -> evaluate */
                if (nexthdr == NEXTHDR_ESP) {
                        temp |= MASK_ESP;
                        break;
                }

                hp = skb_header_pointer(skb, ptr, sizeof(_hdr), &_hdr);
                if (!hp) {
                        par->hotdrop = true;
                        return false;
                }

                /* Calculate the header length */
                if (nexthdr == NEXTHDR_FRAGMENT)
                        hdrlen = 8;
                else if (nexthdr == NEXTHDR_AUTH)
                        hdrlen = ipv6_authlen(hp);
                else
                        hdrlen = ipv6_optlen(hp);

                /* set the flag */
                switch (nexthdr) {
                case NEXTHDR_HOP:
                        temp |= MASK_HOPOPTS;
                        break;
                case NEXTHDR_ROUTING:
                        temp |= MASK_ROUTING;
                        break;
                case NEXTHDR_FRAGMENT:
                        temp |= MASK_FRAGMENT;
                        break;
                case NEXTHDR_AUTH:
                        temp |= MASK_AH;
                        break;
                case NEXTHDR_DEST:
                        temp |= MASK_DSTOPTS;
                        break;
                default:
                        return false;
                }

                nexthdr = hp->nexthdr;
                len -= hdrlen;
                ptr += hdrlen;
                if (ptr > skb->len)
                        break;
        }

        if (nexthdr != NEXTHDR_NONE && nexthdr != NEXTHDR_ESP)
                temp |= MASK_PROTO;

        if (info->modeflag)
                return !((temp ^ info->matchflags ^ info->invflags)
                         & info->matchflags);
        else {
                if (info->invflags)
                        return temp != info->matchflags;
                else
                        return temp == info->matchflags;
        }
}

static int ipv6header_mt6_check(const struct xt_mtchk_param *par)
{
        const struct ip6t_ipv6header_info *info = par->matchinfo;

        /* invflags is 0 or 0xff in hard mode */
        if ((!info->modeflag) && info->invflags != 0x00 &&
            info->invflags != 0xFF)
                return -EINVAL;

        return 0;
}

static struct xt_match ipv6header_mt6_reg __read_mostly = {
        .name           = "ipv6header",
        .family         = NFPROTO_IPV6,
        .match          = ipv6header_mt6,
        .matchsize      = sizeof(struct ip6t_ipv6header_info),
        .checkentry     = ipv6header_mt6_check,
        .destroy        = NULL,
        .me             = THIS_MODULE,
};

static int __init ipv6header_mt6_init(void)
{
        return xt_register_match(&ipv6header_mt6_reg);
}

static void __exit ipv6header_mt6_exit(void)
{
        xt_unregister_match(&ipv6header_mt6_reg);
}

module_init(ipv6header_mt6_init);
module_exit(ipv6header_mt6_exit);