ip6t_hbh.c

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

/* (C) 2001-2002 Andras Kis-Szabo <[email protected]>
 *
 * 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.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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/x_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_opts.h>

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Xtables: IPv6 Hop-By-Hop and Destination Header match");
MODULE_AUTHOR("Andras Kis-Szabo <[email protected]>");
MODULE_ALIAS("ip6t_dst");

/*
 *  (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 struct xt_match hbh_mt6_reg[] __read_mostly;

static bool
hbh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct ipv6_opt_hdr _optsh;
    const struct ipv6_opt_hdr *oh;
    const struct ip6t_opts *optinfo = par->matchinfo;
    unsigned int temp;
    unsigned int ptr = 0;
    unsigned int hdrlen = 0;
    bool ret = false;
    u8 _opttype;
    u8 _optlen;
    const u_int8_t *tp = NULL;
    const u_int8_t *lp = NULL;
    unsigned int optlen;
    int err;

    err = ipv6_find_hdr(skb, &ptr,
                (par->match == &hbh_mt6_reg[0]) ?
                NEXTHDR_HOP : NEXTHDR_DEST, NULL, NULL);
    if (err < 0) {
        if (err != -ENOENT)
            par->hotdrop = true;
        return false;
    }

    oh = skb_header_pointer(skb, ptr, sizeof(_optsh), &_optsh);
    if (oh == NULL) {
        par->hotdrop = true;
        return false;
    }

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

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

    pr_debug("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 {
        pr_debug("Strict ");
        pr_debug("#%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) {
                pr_debug("Tbad %02X %02X\n", *tp,
                     (optinfo->opts[temp] & 0xFF00) >> 8);
                return false;
            } else {
                pr_debug("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) {
                    pr_debug("Lbad %02X %04X\n", *lp,
                         spec_len);
                    return false;
                }
                pr_debug("Lok ");
                optlen = *lp + 2;
            } else {
                pr_debug("Pad1\n");
                optlen = 1;
            }

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

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

    return false;
}

static int hbh_mt6_check(const struct xt_mtchk_param *par)
{
    const struct ip6t_opts *optsinfo = par->matchinfo;

    if (optsinfo->invflags & ~IP6T_OPTS_INV_MASK) {
        pr_debug("unknown flags %X\n", optsinfo->invflags);
        return -EINVAL;
    }

    if (optsinfo->flags & IP6T_OPTS_NSTRICT) {
        pr_debug("Not strict - not implemented");
        return -EINVAL;
    }

    return 0;
}

static struct xt_match hbh_mt6_reg[] __read_mostly = {
    {
        /* Note, hbh_mt6 relies on the order of hbh_mt6_reg */
        .name       = "hbh",
        .family     = NFPROTO_IPV6,
        .match      = hbh_mt6,
        .matchsize  = sizeof(struct ip6t_opts),
        .checkentry = hbh_mt6_check,
        .me     = THIS_MODULE,
    },
    {
        .name       = "dst",
        .family     = NFPROTO_IPV6,
        .match      = hbh_mt6,
        .matchsize  = sizeof(struct ip6t_opts),
        .checkentry = hbh_mt6_check,
        .me     = THIS_MODULE,
    },
};

static int __init hbh_mt6_init(void)
{
    return xt_register_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
}

static void __exit hbh_mt6_exit(void)
{
    xt_unregister_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
}

module_init(hbh_mt6_init);
module_exit(hbh_mt6_exit);