// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Transparent proxy support for Linux/iptables
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*
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* Copyright (C) 2007-2008 BalaBit IT Ltd.
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* Author: Krisztian Kovacs
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#include <net/tcp.h>
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#include <net/udp.h>
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#include <net/icmp.h>
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#include <net/sock.h>
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#include <net/inet_sock.h>
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#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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#include <linux/netfilter_ipv6/ip6_tables.h>
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#include <net/inet6_hashtables.h>
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#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
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#endif
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#include <net/netfilter/nf_socket.h>
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#include <linux/netfilter/xt_socket.h>
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/* "socket" match based redirection (no specific rule)
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* ===================================================
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*
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* There are connections with dynamic endpoints (e.g. FTP data
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* connection) that the user is unable to add explicit rules
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* for. These are taken care of by a generic "socket" rule. It is
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* assumed that the proxy application is trusted to open such
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* connections without explicit iptables rule (except of course the
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* generic 'socket' rule). In this case the following sockets are
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* matched in preference order:
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*
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* - match: if there's a fully established connection matching the
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* _packet_ tuple
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*
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* - match: if there's a non-zero bound listener (possibly with a
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* non-local address) We don't accept zero-bound listeners, since
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* then local services could intercept traffic going through the
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* box.
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*/
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static bool
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socket_match(const struct sk_buff *skb, struct xt_action_param *par,
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const struct xt_socket_mtinfo1 *info)
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{
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struct sk_buff *pskb = (struct sk_buff *)skb;
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struct sock *sk = skb->sk;
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if (sk && !net_eq(xt_net(par), sock_net(sk)))
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sk = NULL;
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if (!sk)
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sk = nf_sk_lookup_slow_v4(xt_net(par), skb, xt_in(par));
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if (sk) {
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bool wildcard;
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bool transparent = true;
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/* Ignore sockets listening on INADDR_ANY,
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* unless XT_SOCKET_NOWILDCARD is set
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*/
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wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
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sk_fullsock(sk) &&
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inet_sk(sk)->inet_rcv_saddr == 0);
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/* Ignore non-transparent sockets,
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* if XT_SOCKET_TRANSPARENT is used
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*/
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if (info->flags & XT_SOCKET_TRANSPARENT)
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transparent = inet_sk_transparent(sk);
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if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
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transparent && sk_fullsock(sk))
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pskb->mark = sk->sk_mark;
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if (sk != skb->sk)
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sock_gen_put(sk);
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if (wildcard || !transparent)
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sk = NULL;
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}
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return sk != NULL;
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}
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static bool
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socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
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{
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static struct xt_socket_mtinfo1 xt_info_v0 = {
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.flags = 0,
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};
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return socket_match(skb, par, &xt_info_v0);
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}
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static bool
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socket_mt4_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
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{
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return socket_match(skb, par, par->matchinfo);
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}
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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static bool
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socket_mt6_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
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{
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const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
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struct sk_buff *pskb = (struct sk_buff *)skb;
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struct sock *sk = skb->sk;
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if (sk && !net_eq(xt_net(par), sock_net(sk)))
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sk = NULL;
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if (!sk)
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sk = nf_sk_lookup_slow_v6(xt_net(par), skb, xt_in(par));
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if (sk) {
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bool wildcard;
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bool transparent = true;
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/* Ignore sockets listening on INADDR_ANY
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* unless XT_SOCKET_NOWILDCARD is set
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*/
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wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
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sk_fullsock(sk) &&
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ipv6_addr_any(&sk->sk_v6_rcv_saddr));
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/* Ignore non-transparent sockets,
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* if XT_SOCKET_TRANSPARENT is used
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*/
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if (info->flags & XT_SOCKET_TRANSPARENT)
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transparent = inet_sk_transparent(sk);
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if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
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transparent && sk_fullsock(sk))
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pskb->mark = sk->sk_mark;
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if (sk != skb->sk)
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sock_gen_put(sk);
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if (wildcard || !transparent)
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sk = NULL;
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}
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return sk != NULL;
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}
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#endif
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static int socket_mt_enable_defrag(struct net *net, int family)
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{
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switch (family) {
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case NFPROTO_IPV4:
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return nf_defrag_ipv4_enable(net);
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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case NFPROTO_IPV6:
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return nf_defrag_ipv6_enable(net);
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#endif
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}
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WARN_ONCE(1, "Unknown family %d\n", family);
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return 0;
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}
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static int socket_mt_v1_check(const struct xt_mtchk_param *par)
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{
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const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
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int err;
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err = socket_mt_enable_defrag(par->net, par->family);
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if (err)
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return err;
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if (info->flags & ~XT_SOCKET_FLAGS_V1) {
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pr_info_ratelimited("unknown flags 0x%x\n",
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info->flags & ~XT_SOCKET_FLAGS_V1);
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return -EINVAL;
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}
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return 0;
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}
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static int socket_mt_v2_check(const struct xt_mtchk_param *par)
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{
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const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
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int err;
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err = socket_mt_enable_defrag(par->net, par->family);
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if (err)
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return err;
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if (info->flags & ~XT_SOCKET_FLAGS_V2) {
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pr_info_ratelimited("unknown flags 0x%x\n",
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info->flags & ~XT_SOCKET_FLAGS_V2);
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return -EINVAL;
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}
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return 0;
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}
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static int socket_mt_v3_check(const struct xt_mtchk_param *par)
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{
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const struct xt_socket_mtinfo3 *info =
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(struct xt_socket_mtinfo3 *)par->matchinfo;
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int err;
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err = socket_mt_enable_defrag(par->net, par->family);
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if (err)
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return err;
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if (info->flags & ~XT_SOCKET_FLAGS_V3) {
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pr_info_ratelimited("unknown flags 0x%x\n",
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info->flags & ~XT_SOCKET_FLAGS_V3);
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return -EINVAL;
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}
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return 0;
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}
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static struct xt_match socket_mt_reg[] __read_mostly = {
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{
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.name = "socket",
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.revision = 0,
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.family = NFPROTO_IPV4,
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.match = socket_mt4_v0,
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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{
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.name = "socket",
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.revision = 1,
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.family = NFPROTO_IPV4,
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.match = socket_mt4_v1_v2_v3,
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.checkentry = socket_mt_v1_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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{
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.name = "socket",
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.revision = 1,
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.family = NFPROTO_IPV6,
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.match = socket_mt6_v1_v2_v3,
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.checkentry = socket_mt_v1_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#endif
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{
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.name = "socket",
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.revision = 2,
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.family = NFPROTO_IPV4,
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.match = socket_mt4_v1_v2_v3,
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.checkentry = socket_mt_v2_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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{
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.name = "socket",
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.revision = 2,
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.family = NFPROTO_IPV6,
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.match = socket_mt6_v1_v2_v3,
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.checkentry = socket_mt_v2_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#endif
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{
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.name = "socket",
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.revision = 3,
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.family = NFPROTO_IPV4,
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.match = socket_mt4_v1_v2_v3,
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.checkentry = socket_mt_v3_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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{
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.name = "socket",
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.revision = 3,
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.family = NFPROTO_IPV6,
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.match = socket_mt6_v1_v2_v3,
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.checkentry = socket_mt_v3_check,
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.matchsize = sizeof(struct xt_socket_mtinfo1),
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.hooks = (1 << NF_INET_PRE_ROUTING) |
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(1 << NF_INET_LOCAL_IN),
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.me = THIS_MODULE,
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},
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#endif
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};
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static int __init socket_mt_init(void)
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{
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return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
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}
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static void __exit socket_mt_exit(void)
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{
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xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
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}
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module_init(socket_mt_init);
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module_exit(socket_mt_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
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MODULE_DESCRIPTION("x_tables socket match module");
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MODULE_ALIAS("ipt_socket");
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MODULE_ALIAS("ip6t_socket");
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