ip6t_rpfilter.c

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/*
 * Copyright (c) 2011 Florian Westphal <[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/netdevice.h>
#include <linux/route.h>
#include <net/ip6_fib.h>
#include <net/ip6_route.h>

#include <linux/netfilter/xt_rpfilter.h>
#include <linux/netfilter/x_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Florian Westphal <[email protected]>");
MODULE_DESCRIPTION("Xtables: IPv6 reverse path filter match");

static bool rpfilter_addr_unicast(const struct in6_addr *addr)
{
    int addr_type = ipv6_addr_type(addr);
    return addr_type & IPV6_ADDR_UNICAST;
}

static bool rpfilter_lookup_reverse6(const struct sk_buff *skb,
                     const struct net_device *dev, u8 flags)
{
    struct rt6_info *rt;
    struct ipv6hdr *iph = ipv6_hdr(skb);
    bool ret = false;
    struct flowi6 fl6 = {
        .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
        .flowi6_proto = iph->nexthdr,
        .daddr = iph->saddr,
    };
    int lookup_flags;

    if (rpfilter_addr_unicast(&iph->daddr)) {
        memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
        lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
    } else {
        lookup_flags = 0;
    }

    fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
    if ((flags & XT_RPFILTER_LOOSE) == 0) {
        fl6.flowi6_oif = dev->ifindex;
        lookup_flags |= RT6_LOOKUP_F_IFACE;
    }

    rt = (void *) ip6_route_lookup(dev_net(dev), &fl6, lookup_flags);
    if (rt->dst.error)
        goto out;

    if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
        goto out;

    if (rt->rt6i_flags & RTF_LOCAL) {
        ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
        goto out;
    }

    if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
        ret = true;
 out:
    dst_release(&rt->dst);
    return ret;
}

static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct xt_rpfilter_info *info = par->matchinfo;
    int saddrtype;
    struct ipv6hdr *iph;
    bool invert = info->flags & XT_RPFILTER_INVERT;

    if (par->in->flags & IFF_LOOPBACK)
        return true ^ invert;

    iph = ipv6_hdr(skb);
    saddrtype = ipv6_addr_type(&iph->saddr);
    if (unlikely(saddrtype == IPV6_ADDR_ANY))
        return true ^ invert; /* not routable: forward path will drop it */

    return rpfilter_lookup_reverse6(skb, par->in, info->flags) ^ invert;
}

static int rpfilter_check(const struct xt_mtchk_param *par)
{
    const struct xt_rpfilter_info *info = par->matchinfo;
    unsigned int options = ~XT_RPFILTER_OPTION_MASK;

    if (info->flags & options) {
        pr_info("unknown options encountered");
        return -EINVAL;
    }

    if (strcmp(par->table, "mangle") != 0 &&
        strcmp(par->table, "raw") != 0) {
        pr_info("match only valid in the \'raw\' "
            "or \'mangle\' tables, not \'%s\'.\n", par->table);
        return -EINVAL;
    }

    return 0;
}

static struct xt_match rpfilter_mt_reg __read_mostly = {
    .name       = "rpfilter",
    .family     = NFPROTO_IPV6,
    .checkentry = rpfilter_check,
    .match      = rpfilter_mt,
    .matchsize  = sizeof(struct xt_rpfilter_info),
    .hooks      = (1 << NF_INET_PRE_ROUTING),
    .me     = THIS_MODULE
};

static int __init rpfilter_mt_init(void)
{
    return xt_register_match(&rpfilter_mt_reg);
}

static void __exit rpfilter_mt_exit(void)
{
    xt_unregister_match(&rpfilter_mt_reg);
}

module_init(rpfilter_mt_init);
module_exit(rpfilter_mt_exit);