xt_owner.c

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/*
 * Kernel module to match various things tied to sockets associated with
 * locally generated outgoing packets.
 *
 * (C) 2000 Marc Boucher <[email protected]>
 *
 * Copyright © CC Computer Consultants GmbH, 2007 - 2008
 *
 * 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.
 */
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/file.h>
#include <net/sock.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_owner.h>

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

    /* For now only allow adding matches from the initial user namespace */
    if ((info->match & (XT_OWNER_UID|XT_OWNER_GID)) &&
        (current_user_ns() != &init_user_ns))
        return -EINVAL;
    return 0;
}

static bool
owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct xt_owner_match_info *info = par->matchinfo;
    const struct file *filp;

    if (skb->sk == NULL || skb->sk->sk_socket == NULL)
        return (info->match ^ info->invert) == 0;
    else if (info->match & info->invert & XT_OWNER_SOCKET)
        /*
         * Socket exists but user wanted ! --socket-exists.
         * (Single ampersands intended.)
         */
        return false;

    filp = skb->sk->sk_socket->file;
    if (filp == NULL)
        return ((info->match ^ info->invert) &
               (XT_OWNER_UID | XT_OWNER_GID)) == 0;

    if (info->match & XT_OWNER_UID) {
        kuid_t uid_min = make_kuid(&init_user_ns, info->uid_min);
        kuid_t uid_max = make_kuid(&init_user_ns, info->uid_max);
        if ((uid_gte(filp->f_cred->fsuid, uid_min) &&
             uid_lte(filp->f_cred->fsuid, uid_max)) ^
            !(info->invert & XT_OWNER_UID))
            return false;
    }

    if (info->match & XT_OWNER_GID) {
        kgid_t gid_min = make_kgid(&init_user_ns, info->gid_min);
        kgid_t gid_max = make_kgid(&init_user_ns, info->gid_max);
        if ((gid_gte(filp->f_cred->fsgid, gid_min) &&
             gid_lte(filp->f_cred->fsgid, gid_max)) ^
            !(info->invert & XT_OWNER_GID))
            return false;
    }

    return true;
}

static struct xt_match owner_mt_reg __read_mostly = {
    .name       = "owner",
    .revision   = 1,
    .family     = NFPROTO_UNSPEC,
    .checkentry = owner_check,
    .match      = owner_mt,
    .matchsize  = sizeof(struct xt_owner_match_info),
    .hooks      = (1 << NF_INET_LOCAL_OUT) |
                  (1 << NF_INET_POST_ROUTING),
    .me         = THIS_MODULE,
};

static int __init owner_mt_init(void)
{
    return xt_register_match(&owner_mt_reg);
}

static void __exit owner_mt_exit(void)
{
    xt_unregister_match(&owner_mt_reg);
}

module_init(owner_mt_init);
module_exit(owner_mt_exit);
MODULE_AUTHOR("Jan Engelhardt <[email protected]>");
MODULE_DESCRIPTION("Xtables: socket owner matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_owner");
MODULE_ALIAS("ip6t_owner");