// SPDX-License-Identifier: GPL-2.0-only
/*
 * Kernel module to match various things tied to sockets associated with
 * locally generated outgoing packets.
 *
 * (C) 2000 Marc Boucher <marc@mbsi.ca>
 *
 * Copyright © CC Computer Consultants GmbH, 2007 - 2008
 */
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/file.h>
#include <linux/cred.h>

#include <net/sock.h>
#include <net/inet_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;
        struct net *net = par->net;

        if (info->match & ~XT_OWNER_MASK)
                return -EINVAL;

        /* Only allow the common case where the userns of the writer
         * matches the userns of the network namespace.
         */
        if ((info->match & (XT_OWNER_UID|XT_OWNER_GID)) &&
            (current_user_ns() != net->user_ns))
                return -EINVAL;

        /* Ensure the uids are valid */
        if (info->match & XT_OWNER_UID) {
                kuid_t uid_min = make_kuid(net->user_ns, info->uid_min);
                kuid_t uid_max = make_kuid(net->user_ns, info->uid_max);

                if (!uid_valid(uid_min) || !uid_valid(uid_max) ||
                    (info->uid_max < info->uid_min) ||
                    uid_lt(uid_max, uid_min)) {
                        return -EINVAL;
                }
        }

        /* Ensure the gids are valid */
        if (info->match & XT_OWNER_GID) {
                kgid_t gid_min = make_kgid(net->user_ns, info->gid_min);
                kgid_t gid_max = make_kgid(net->user_ns, info->gid_max);

                if (!gid_valid(gid_min) || !gid_valid(gid_max) ||
                    (info->gid_max < info->gid_min) ||
                    gid_lt(gid_max, gid_min)) {
                        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;
        struct sock *sk = skb_to_full_sk(skb);
        struct net *net = xt_net(par);

        if (!sk || !sk->sk_socket || !net_eq(net, sock_net(sk)))
                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;

        read_lock_bh(&sk->sk_callback_lock);
        filp = sk->sk_socket ? sk->sk_socket->file : NULL;
        if (filp == NULL) {
                read_unlock_bh(&sk->sk_callback_lock);
                return ((info->match ^ info->invert) &
                       (XT_OWNER_UID | XT_OWNER_GID)) == 0;
        }

        if (info->match & XT_OWNER_UID) {
                kuid_t uid_min = make_kuid(net->user_ns, info->uid_min);
                kuid_t uid_max = make_kuid(net->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)) {
                        read_unlock_bh(&sk->sk_callback_lock);
                        return false;
                }
        }

        if (info->match & XT_OWNER_GID) {
                unsigned int i, match = false;
                kgid_t gid_min = make_kgid(net->user_ns, info->gid_min);
                kgid_t gid_max = make_kgid(net->user_ns, info->gid_max);
                struct group_info *gi = filp->f_cred->group_info;

                if (gid_gte(filp->f_cred->fsgid, gid_min) &&
                    gid_lte(filp->f_cred->fsgid, gid_max))
                        match = true;

                if (!match && (info->match & XT_OWNER_SUPPL_GROUPS) && gi) {
                        for (i = 0; i < gi->ngroups; ++i) {
                                kgid_t group = gi->gid[i];

                                if (gid_gte(group, gid_min) &&
                                    gid_lte(group, gid_max)) {
                                        match = true;
                                        break;
                                }
                        }
                }

                if (match ^ !(info->invert & XT_OWNER_GID)) {
                        read_unlock_bh(&sk->sk_callback_lock);
                        return false;
                }
        }

        read_unlock_bh(&sk->sk_callback_lock);
        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 <jengelh@medozas.de>");
MODULE_DESCRIPTION("Xtables: socket owner matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_owner");
MODULE_ALIAS("ip6t_owner");