xt_policy.c

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/* IP tables module for matching IPsec policy
 *
 * Copyright (c) 2004,2005 Patrick McHardy, <[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/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/init.h>
#include <net/xfrm.h>

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

MODULE_AUTHOR("Patrick McHardy <[email protected]>");
MODULE_DESCRIPTION("Xtables: IPsec policy match");
MODULE_LICENSE("GPL");

static inline bool
xt_addr_cmp(const union nf_inet_addr *a1, const union nf_inet_addr *m,
        const union nf_inet_addr *a2, unsigned short family)
{
    switch (family) {
    case NFPROTO_IPV4:
        return ((a1->ip ^ a2->ip) & m->ip) == 0;
    case NFPROTO_IPV6:
        return ipv6_masked_addr_cmp(&a1->in6, &m->in6, &a2->in6) == 0;
    }
    return false;
}

static bool
match_xfrm_state(const struct xfrm_state *x, const struct xt_policy_elem *e,
         unsigned short family)
{
#define MATCH_ADDR(x,y,z)   (!e->match.x ||                \
                 (xt_addr_cmp(&e->x, &e->y, (const union nf_inet_addr *)(z), family) \
                  ^ e->invert.x))
#define MATCH(x,y)      (!e->match.x || ((e->x == (y)) ^ e->invert.x))

    return MATCH_ADDR(saddr, smask, &x->props.saddr) &&
           MATCH_ADDR(daddr, dmask, &x->id.daddr) &&
           MATCH(proto, x->id.proto) &&
           MATCH(mode, x->props.mode) &&
           MATCH(spi, x->id.spi) &&
           MATCH(reqid, x->props.reqid);
}

static int
match_policy_in(const struct sk_buff *skb, const struct xt_policy_info *info,
        unsigned short family)
{
    const struct xt_policy_elem *e;
    const struct sec_path *sp = skb->sp;
    int strict = info->flags & XT_POLICY_MATCH_STRICT;
    int i, pos;

    if (sp == NULL)
        return -1;
    if (strict && info->len != sp->len)
        return 0;

    for (i = sp->len - 1; i >= 0; i--) {
        pos = strict ? i - sp->len + 1 : 0;
        if (pos >= info->len)
            return 0;
        e = &info->pol[pos];

        if (match_xfrm_state(sp->xvec[i], e, family)) {
            if (!strict)
                return 1;
        } else if (strict)
            return 0;
    }

    return strict ? 1 : 0;
}

static int
match_policy_out(const struct sk_buff *skb, const struct xt_policy_info *info,
         unsigned short family)
{
    const struct xt_policy_elem *e;
    const struct dst_entry *dst = skb_dst(skb);
    int strict = info->flags & XT_POLICY_MATCH_STRICT;
    int i, pos;

    if (dst->xfrm == NULL)
        return -1;

    for (i = 0; dst && dst->xfrm; dst = dst->child, i++) {
        pos = strict ? i : 0;
        if (pos >= info->len)
            return 0;
        e = &info->pol[pos];

        if (match_xfrm_state(dst->xfrm, e, family)) {
            if (!strict)
                return 1;
        } else if (strict)
            return 0;
    }

    return strict ? i == info->len : 0;
}

static bool
policy_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct xt_policy_info *info = par->matchinfo;
    int ret;

    if (info->flags & XT_POLICY_MATCH_IN)
        ret = match_policy_in(skb, info, par->family);
    else
        ret = match_policy_out(skb, info, par->family);

    if (ret < 0)
        ret = info->flags & XT_POLICY_MATCH_NONE ? true : false;
    else if (info->flags & XT_POLICY_MATCH_NONE)
        ret = false;

    return ret;
}

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

    if (!(info->flags & (XT_POLICY_MATCH_IN|XT_POLICY_MATCH_OUT))) {
        pr_info("neither incoming nor outgoing policy selected\n");
        return -EINVAL;
    }
    if (par->hook_mask & ((1 << NF_INET_PRE_ROUTING) |
        (1 << NF_INET_LOCAL_IN)) && info->flags & XT_POLICY_MATCH_OUT) {
        pr_info("output policy not valid in PREROUTING and INPUT\n");
        return -EINVAL;
    }
    if (par->hook_mask & ((1 << NF_INET_POST_ROUTING) |
        (1 << NF_INET_LOCAL_OUT)) && info->flags & XT_POLICY_MATCH_IN) {
        pr_info("input policy not valid in POSTROUTING and OUTPUT\n");
        return -EINVAL;
    }
    if (info->len > XT_POLICY_MAX_ELEM) {
        pr_info("too many policy elements\n");
        return -EINVAL;
    }
    return 0;
}

static struct xt_match policy_mt_reg[] __read_mostly = {
    {
        .name       = "policy",
        .family     = NFPROTO_IPV4,
        .checkentry     = policy_mt_check,
        .match      = policy_mt,
        .matchsize  = sizeof(struct xt_policy_info),
        .me     = THIS_MODULE,
    },
    {
        .name       = "policy",
        .family     = NFPROTO_IPV6,
        .checkentry = policy_mt_check,
        .match      = policy_mt,
        .matchsize  = sizeof(struct xt_policy_info),
        .me     = THIS_MODULE,
    },
};

static int __init policy_mt_init(void)
{
    return xt_register_matches(policy_mt_reg, ARRAY_SIZE(policy_mt_reg));
}

static void __exit policy_mt_exit(void)
{
    xt_unregister_matches(policy_mt_reg, ARRAY_SIZE(policy_mt_reg));
}

module_init(policy_mt_init);
module_exit(policy_mt_exit);
MODULE_ALIAS("ipt_policy");
MODULE_ALIAS("ip6t_policy");