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// SPDX-License-Identifier: GPL-2.0-only
/*
* Transparent proxy support for Linux/iptables
*
* Copyright (C) 2007-2008 BalaBit IT Ltd.
* Author: Krisztian Kovacs
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <net/sock.h>
#include <net/inet_sock.h>
#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <net/inet6_hashtables.h>
#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
#endif
#include <net/netfilter/nf_socket.h>
#include <linux/netfilter/xt_socket.h>
/* "socket" match based redirection (no specific rule)
* ===================================================
*
* There are connections with dynamic endpoints (e.g. FTP data
* connection) that the user is unable to add explicit rules
* for. These are taken care of by a generic "socket" rule. It is
* assumed that the proxy application is trusted to open such
* connections without explicit iptables rule (except of course the
* generic 'socket' rule). In this case the following sockets are
* matched in preference order:
*
* - match: if there's a fully established connection matching the
* _packet_ tuple
*
* - match: if there's a non-zero bound listener (possibly with a
* non-local address) We don't accept zero-bound listeners, since
* then local services could intercept traffic going through the
* box.
*/
static bool
socket_match(const struct sk_buff *skb, struct xt_action_param *par,
const struct xt_socket_mtinfo1 *info)
{
struct sk_buff *pskb = (struct sk_buff *)skb;
struct sock *sk = skb->sk;
if (sk && !net_eq(xt_net(par), sock_net(sk)))
sk = NULL;
if (!sk)
sk = nf_sk_lookup_slow_v4(xt_net(par), skb, xt_in(par));
if (sk) {
bool wildcard;
bool transparent = true;
/* Ignore sockets listening on INADDR_ANY,
* unless XT_SOCKET_NOWILDCARD is set
*/
wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
sk_fullsock(sk) &&
inet_sk(sk)->inet_rcv_saddr == 0);
/* Ignore non-transparent sockets,
* if XT_SOCKET_TRANSPARENT is used
*/
if (info->flags & XT_SOCKET_TRANSPARENT)
transparent = inet_sk_transparent(sk);
if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
transparent && sk_fullsock(sk))
pskb->mark = READ_ONCE(sk->sk_mark);
if (sk != skb->sk)
sock_gen_put(sk);
if (wildcard || !transparent)
sk = NULL;
}
return sk != NULL;
}
static bool
socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
{
static struct xt_socket_mtinfo1 xt_info_v0 = {
.flags = 0,
};
return socket_match(skb, par, &xt_info_v0);
}
static bool
socket_mt4_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
{
return socket_match(skb, par, par->matchinfo);
}
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static bool
socket_mt6_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
struct sk_buff *pskb = (struct sk_buff *)skb;
struct sock *sk = skb->sk;
if (sk && !net_eq(xt_net(par), sock_net(sk)))
sk = NULL;
if (!sk)
sk = nf_sk_lookup_slow_v6(xt_net(par), skb, xt_in(par));
if (sk) {
bool wildcard;
bool transparent = true;
/* Ignore sockets listening on INADDR_ANY
* unless XT_SOCKET_NOWILDCARD is set
*/
wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
sk_fullsock(sk) &&
ipv6_addr_any(&sk->sk_v6_rcv_saddr));
/* Ignore non-transparent sockets,
* if XT_SOCKET_TRANSPARENT is used
*/
if (info->flags & XT_SOCKET_TRANSPARENT)
transparent = inet_sk_transparent(sk);
if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
transparent && sk_fullsock(sk))
pskb->mark = READ_ONCE(sk->sk_mark);
if (sk != skb->sk)
sock_gen_put(sk);
if (wildcard || !transparent)
sk = NULL;
}
return sk != NULL;
}
#endif
static int socket_mt_enable_defrag(struct net *net, int family)
{
switch (family) {
case NFPROTO_IPV4:
return nf_defrag_ipv4_enable(net);
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
case NFPROTO_IPV6:
return nf_defrag_ipv6_enable(net);
#endif
}
WARN_ONCE(1, "Unknown family %d\n", family);
return 0;
}
static int socket_mt_v1_check(const struct xt_mtchk_param *par)
{
const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
int err;
err = socket_mt_enable_defrag(par->net, par->family);
if (err)
return err;
if (info->flags & ~XT_SOCKET_FLAGS_V1) {
pr_info_ratelimited("unknown flags 0x%x\n",
info->flags & ~XT_SOCKET_FLAGS_V1);
return -EINVAL;
}
return 0;
}
static int socket_mt_v2_check(const struct xt_mtchk_param *par)
{
const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
int err;
err = socket_mt_enable_defrag(par->net, par->family);
if (err)
return err;
if (info->flags & ~XT_SOCKET_FLAGS_V2) {
pr_info_ratelimited("unknown flags 0x%x\n",
info->flags & ~XT_SOCKET_FLAGS_V2);
return -EINVAL;
}
return 0;
}
static int socket_mt_v3_check(const struct xt_mtchk_param *par)
{
const struct xt_socket_mtinfo3 *info =
(struct xt_socket_mtinfo3 *)par->matchinfo;
int err;
err = socket_mt_enable_defrag(par->net, par->family);
if (err)
return err;
if (info->flags & ~XT_SOCKET_FLAGS_V3) {
pr_info_ratelimited("unknown flags 0x%x\n",
info->flags & ~XT_SOCKET_FLAGS_V3);
return -EINVAL;
}
return 0;
}
static void socket_mt_destroy(const struct xt_mtdtor_param *par)
{
if (par->family == NFPROTO_IPV4)
nf_defrag_ipv4_disable(par->net);
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
else if (par->family == NFPROTO_IPV6)
nf_defrag_ipv6_disable(par->net);
#endif
}
static struct xt_match socket_mt_reg[] __read_mostly = {
{
.name = "socket",
.revision = 0,
.family = NFPROTO_IPV4,
.match = socket_mt4_v0,
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
{
.name = "socket",
.revision = 1,
.family = NFPROTO_IPV4,
.match = socket_mt4_v1_v2_v3,
.destroy = socket_mt_destroy,
.checkentry = socket_mt_v1_check,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
{
.name = "socket",
.revision = 1,
.family = NFPROTO_IPV6,
.match = socket_mt6_v1_v2_v3,
.checkentry = socket_mt_v1_check,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.destroy = socket_mt_destroy,
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#endif
{
.name = "socket",
.revision = 2,
.family = NFPROTO_IPV4,
.match = socket_mt4_v1_v2_v3,
.checkentry = socket_mt_v2_check,
.destroy = socket_mt_destroy,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
{
.name = "socket",
.revision = 2,
.family = NFPROTO_IPV6,
.match = socket_mt6_v1_v2_v3,
.checkentry = socket_mt_v2_check,
.destroy = socket_mt_destroy,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#endif
{
.name = "socket",
.revision = 3,
.family = NFPROTO_IPV4,
.match = socket_mt4_v1_v2_v3,
.checkentry = socket_mt_v3_check,
.destroy = socket_mt_destroy,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
{
.name = "socket",
.revision = 3,
.family = NFPROTO_IPV6,
.match = socket_mt6_v1_v2_v3,
.checkentry = socket_mt_v3_check,
.destroy = socket_mt_destroy,
.matchsize = sizeof(struct xt_socket_mtinfo1),
.hooks = (1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN),
.me = THIS_MODULE,
},
#endif
};
static int __init socket_mt_init(void)
{
return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
}
static void __exit socket_mt_exit(void)
{
xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
}
module_init(socket_mt_init);
module_exit(socket_mt_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
MODULE_DESCRIPTION("x_tables socket match module");
MODULE_ALIAS("ipt_socket");
MODULE_ALIAS("ip6t_socket");
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