root/net/ipv6/netfilter/ip6t_HL.c

DEFINITIONS

1. hl_tg6
2. hl_tg6_check
3. hl_tg6_init
4. hl_tg6_exit

/*
 * Hop Limit modification target for ip6tables
 * Maciej Soltysiak <solt@dns.toxicfilms.tv>
 * Based on HW's TTL module
 *
 * This software is distributed under the terms of GNU GPL
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv6/ip6t_HL.h>

MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
MODULE_DESCRIPTION("Xtables: IPv6 Hop Limit field modification target");
MODULE_LICENSE("GPL");

static unsigned int
hl_tg6(struct sk_buff *skb, const struct xt_target_param *par)
{
        struct ipv6hdr *ip6h;
        const struct ip6t_HL_info *info = par->targinfo;
        int new_hl;

        if (!skb_make_writable(skb, skb->len))
                return NF_DROP;

        ip6h = ipv6_hdr(skb);

        switch (info->mode) {
                case IP6T_HL_SET:
                        new_hl = info->hop_limit;
                        break;
                case IP6T_HL_INC:
                        new_hl = ip6h->hop_limit + info->hop_limit;
                        if (new_hl > 255)
                                new_hl = 255;
                        break;
                case IP6T_HL_DEC:
                        new_hl = ip6h->hop_limit - info->hop_limit;
                        if (new_hl < 0)
                                new_hl = 0;
                        break;
                default:
                        new_hl = ip6h->hop_limit;
                        break;
        }

        ip6h->hop_limit = new_hl;

        return XT_CONTINUE;
}

static bool hl_tg6_check(const struct xt_tgchk_param *par)
{
        const struct ip6t_HL_info *info = par->targinfo;

        if (info->mode > IP6T_HL_MAXMODE) {
                printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
                        info->mode);
                return false;
        }
        if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
                printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
                        "make sense with value 0\n");
                return false;
        }
        return true;
}

static struct xt_target hl_tg6_reg __read_mostly = {
        .name           = "HL",
        .family         = NFPROTO_IPV6,
        .target         = hl_tg6,
        .targetsize     = sizeof(struct ip6t_HL_info),
        .table          = "mangle",
        .checkentry     = hl_tg6_check,
        .me             = THIS_MODULE
};

static int __init hl_tg6_init(void)
{
        return xt_register_target(&hl_tg6_reg);
}

static void __exit hl_tg6_exit(void)
{
        xt_unregister_target(&hl_tg6_reg);
}

module_init(hl_tg6_init);
module_exit(hl_tg6_exit);