ip6t_frag.c

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/* Kernel module to match FRAG 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 <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_frag.h>

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Xtables: IPv6 fragment match");
MODULE_AUTHOR("Andras Kis-Szabo <[email protected]>");

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

static bool
frag_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct frag_hdr _frag;
    const struct frag_hdr *fh;
    const struct ip6t_frag *fraginfo = par->matchinfo;
    unsigned int ptr = 0;
    int err;

    err = ipv6_find_hdr(skb, &ptr, NEXTHDR_FRAGMENT, NULL, NULL);
    if (err < 0) {
        if (err != -ENOENT)
            par->hotdrop = true;
        return false;
    }

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

    pr_debug("INFO %04X ", fh->frag_off);
    pr_debug("OFFSET %04X ", ntohs(fh->frag_off) & ~0x7);
    pr_debug("RES %02X %04X", fh->reserved, ntohs(fh->frag_off) & 0x6);
    pr_debug("MF %04X ", fh->frag_off & htons(IP6_MF));
    pr_debug("ID %u %08X\n", ntohl(fh->identification),
         ntohl(fh->identification));

    pr_debug("IPv6 FRAG id %02X ",
         id_match(fraginfo->ids[0], fraginfo->ids[1],
              ntohl(fh->identification),
              !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)));
    pr_debug("res %02X %02X%04X %02X ",
         fraginfo->flags & IP6T_FRAG_RES, fh->reserved,
         ntohs(fh->frag_off) & 0x6,
         !((fraginfo->flags & IP6T_FRAG_RES) &&
           (fh->reserved || (ntohs(fh->frag_off) & 0x06))));
    pr_debug("first %02X %02X %02X ",
         fraginfo->flags & IP6T_FRAG_FST,
         ntohs(fh->frag_off) & ~0x7,
         !((fraginfo->flags & IP6T_FRAG_FST) &&
           (ntohs(fh->frag_off) & ~0x7)));
    pr_debug("mf %02X %02X %02X ",
         fraginfo->flags & IP6T_FRAG_MF,
         ntohs(fh->frag_off) & IP6_MF,
         !((fraginfo->flags & IP6T_FRAG_MF) &&
           !((ntohs(fh->frag_off) & IP6_MF))));
    pr_debug("last %02X %02X %02X\n",
         fraginfo->flags & IP6T_FRAG_NMF,
         ntohs(fh->frag_off) & IP6_MF,
         !((fraginfo->flags & IP6T_FRAG_NMF) &&
           (ntohs(fh->frag_off) & IP6_MF)));

    return (fh != NULL) &&
        id_match(fraginfo->ids[0], fraginfo->ids[1],
             ntohl(fh->identification),
             !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)) &&
        !((fraginfo->flags & IP6T_FRAG_RES) &&
          (fh->reserved || (ntohs(fh->frag_off) & 0x6))) &&
        !((fraginfo->flags & IP6T_FRAG_FST) &&
          (ntohs(fh->frag_off) & ~0x7)) &&
        !((fraginfo->flags & IP6T_FRAG_MF) &&
          !(ntohs(fh->frag_off) & IP6_MF)) &&
        !((fraginfo->flags & IP6T_FRAG_NMF) &&
          (ntohs(fh->frag_off) & IP6_MF));
}

static int frag_mt6_check(const struct xt_mtchk_param *par)
{
    const struct ip6t_frag *fraginfo = par->matchinfo;

    if (fraginfo->invflags & ~IP6T_FRAG_INV_MASK) {
        pr_debug("unknown flags %X\n", fraginfo->invflags);
        return -EINVAL;
    }
    return 0;
}

static struct xt_match frag_mt6_reg __read_mostly = {
    .name       = "frag",
    .family     = NFPROTO_IPV6,
    .match      = frag_mt6,
    .matchsize  = sizeof(struct ip6t_frag),
    .checkentry = frag_mt6_check,
    .me     = THIS_MODULE,
};

static int __init frag_mt6_init(void)
{
    return xt_register_match(&frag_mt6_reg);
}

static void __exit frag_mt6_exit(void)
{
    xt_unregister_match(&frag_mt6_reg);
}

module_init(frag_mt6_init);
module_exit(frag_mt6_exit);