1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Transparent proxy support for Linux/iptables
4 *
5 * Copyright (c) 2006-2010 BalaBit IT Ltd.
6 * Author: Balazs Scheidler, Krisztian Kovacs
7 */
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 #include <linux/module.h>
10 #include <linux/skbuff.h>
11 #include <linux/ip.h>
12 #include <net/checksum.h>
13 #include <net/udp.h>
14 #include <net/tcp.h>
15 #include <net/inet_sock.h>
16 #include <net/inet_hashtables.h>
17 #include <linux/inetdevice.h>
18 #include <linux/netfilter/x_tables.h>
19 #include <linux/netfilter_ipv4/ip_tables.h>
20
21 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
22
23 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
24 #define XT_TPROXY_HAVE_IPV6 1
25 #include <net/if_inet6.h>
26 #include <net/addrconf.h>
27 #include <net/inet6_hashtables.h>
28 #include <linux/netfilter_ipv6/ip6_tables.h>
29 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
30 #endif
31
32 #include <net/netfilter/nf_tproxy.h>
33 #include <linux/netfilter/xt_TPROXY.h>
34
35 static unsigned int
tproxy_tg4(struct net * net,struct sk_buff * skb,__be32 laddr,__be16 lport,u_int32_t mark_mask,u_int32_t mark_value)36 tproxy_tg4(struct net *net, struct sk_buff *skb, __be32 laddr, __be16 lport,
37 u_int32_t mark_mask, u_int32_t mark_value)
38 {
39 const struct iphdr *iph = ip_hdr(skb);
40 struct udphdr _hdr, *hp;
41 struct sock *sk;
42
43 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
44 if (hp == NULL)
45 return NF_DROP;
46
47 /* check if there's an ongoing connection on the packet
48 * addresses, this happens if the redirect already happened
49 * and the current packet belongs to an already established
50 * connection */
51 sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
52 iph->saddr, iph->daddr,
53 hp->source, hp->dest,
54 skb->dev, NF_TPROXY_LOOKUP_ESTABLISHED);
55
56 laddr = nf_tproxy_laddr4(skb, laddr, iph->daddr);
57 if (!lport)
58 lport = hp->dest;
59
60 /* UDP has no TCP_TIME_WAIT state, so we never enter here */
61 if (sk && sk->sk_state == TCP_TIME_WAIT)
62 /* reopening a TIME_WAIT connection needs special handling */
63 sk = nf_tproxy_handle_time_wait4(net, skb, laddr, lport, sk);
64 else if (!sk)
65 /* no, there's no established connection, check if
66 * there's a listener on the redirected addr/port */
67 sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
68 iph->saddr, laddr,
69 hp->source, lport,
70 skb->dev, NF_TPROXY_LOOKUP_LISTENER);
71
72 /* NOTE: assign_sock consumes our sk reference */
73 if (sk && nf_tproxy_sk_is_transparent(sk)) {
74 /* This should be in a separate target, but we don't do multiple
75 targets on the same rule yet */
76 skb->mark = (skb->mark & ~mark_mask) ^ mark_value;
77
78 pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
79 iph->protocol, &iph->daddr, ntohs(hp->dest),
80 &laddr, ntohs(lport), skb->mark);
81
82 nf_tproxy_assign_sock(skb, sk);
83 return NF_ACCEPT;
84 }
85
86 pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
87 iph->protocol, &iph->saddr, ntohs(hp->source),
88 &iph->daddr, ntohs(hp->dest), skb->mark);
89 return NF_DROP;
90 }
91
92 static unsigned int
tproxy_tg4_v0(struct sk_buff * skb,const struct xt_action_param * par)93 tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
94 {
95 const struct xt_tproxy_target_info *tgi = par->targinfo;
96
97 return tproxy_tg4(xt_net(par), skb, tgi->laddr, tgi->lport,
98 tgi->mark_mask, tgi->mark_value);
99 }
100
101 static unsigned int
tproxy_tg4_v1(struct sk_buff * skb,const struct xt_action_param * par)102 tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
103 {
104 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
105
106 return tproxy_tg4(xt_net(par), skb, tgi->laddr.ip, tgi->lport,
107 tgi->mark_mask, tgi->mark_value);
108 }
109
110 #ifdef XT_TPROXY_HAVE_IPV6
111
112 static unsigned int
tproxy_tg6_v1(struct sk_buff * skb,const struct xt_action_param * par)113 tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
114 {
115 const struct ipv6hdr *iph = ipv6_hdr(skb);
116 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
117 struct udphdr _hdr, *hp;
118 struct sock *sk;
119 const struct in6_addr *laddr;
120 __be16 lport;
121 int thoff = 0;
122 int tproto;
123
124 tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
125 if (tproto < 0) {
126 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
127 return NF_DROP;
128 }
129
130 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
131 if (hp == NULL) {
132 pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
133 return NF_DROP;
134 }
135
136 /* check if there's an ongoing connection on the packet
137 * addresses, this happens if the redirect already happened
138 * and the current packet belongs to an already established
139 * connection */
140 sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff, tproto,
141 &iph->saddr, &iph->daddr,
142 hp->source, hp->dest,
143 xt_in(par), NF_TPROXY_LOOKUP_ESTABLISHED);
144
145 laddr = nf_tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
146 lport = tgi->lport ? tgi->lport : hp->dest;
147
148 /* UDP has no TCP_TIME_WAIT state, so we never enter here */
149 if (sk && sk->sk_state == TCP_TIME_WAIT) {
150 const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
151 /* reopening a TIME_WAIT connection needs special handling */
152 sk = nf_tproxy_handle_time_wait6(skb, tproto, thoff,
153 xt_net(par),
154 &tgi->laddr.in6,
155 tgi->lport,
156 sk);
157 }
158 else if (!sk)
159 /* no there's no established connection, check if
160 * there's a listener on the redirected addr/port */
161 sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff,
162 tproto, &iph->saddr, laddr,
163 hp->source, lport,
164 xt_in(par), NF_TPROXY_LOOKUP_LISTENER);
165
166 /* NOTE: assign_sock consumes our sk reference */
167 if (sk && nf_tproxy_sk_is_transparent(sk)) {
168 /* This should be in a separate target, but we don't do multiple
169 targets on the same rule yet */
170 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
171
172 pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
173 tproto, &iph->saddr, ntohs(hp->source),
174 laddr, ntohs(lport), skb->mark);
175
176 nf_tproxy_assign_sock(skb, sk);
177 return NF_ACCEPT;
178 }
179
180 pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
181 tproto, &iph->saddr, ntohs(hp->source),
182 &iph->daddr, ntohs(hp->dest), skb->mark);
183
184 return NF_DROP;
185 }
186
tproxy_tg6_check(const struct xt_tgchk_param * par)187 static int tproxy_tg6_check(const struct xt_tgchk_param *par)
188 {
189 const struct ip6t_ip6 *i = par->entryinfo;
190 int err;
191
192 err = nf_defrag_ipv6_enable(par->net);
193 if (err)
194 return err;
195
196 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) &&
197 !(i->invflags & IP6T_INV_PROTO))
198 return 0;
199
200 pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
201 return -EINVAL;
202 }
203 #endif
204
tproxy_tg4_check(const struct xt_tgchk_param * par)205 static int tproxy_tg4_check(const struct xt_tgchk_param *par)
206 {
207 const struct ipt_ip *i = par->entryinfo;
208 int err;
209
210 err = nf_defrag_ipv4_enable(par->net);
211 if (err)
212 return err;
213
214 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
215 && !(i->invflags & IPT_INV_PROTO))
216 return 0;
217
218 pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
219 return -EINVAL;
220 }
221
222 static struct xt_target tproxy_tg_reg[] __read_mostly = {
223 {
224 .name = "TPROXY",
225 .family = NFPROTO_IPV4,
226 .table = "mangle",
227 .target = tproxy_tg4_v0,
228 .revision = 0,
229 .targetsize = sizeof(struct xt_tproxy_target_info),
230 .checkentry = tproxy_tg4_check,
231 .hooks = 1 << NF_INET_PRE_ROUTING,
232 .me = THIS_MODULE,
233 },
234 {
235 .name = "TPROXY",
236 .family = NFPROTO_IPV4,
237 .table = "mangle",
238 .target = tproxy_tg4_v1,
239 .revision = 1,
240 .targetsize = sizeof(struct xt_tproxy_target_info_v1),
241 .checkentry = tproxy_tg4_check,
242 .hooks = 1 << NF_INET_PRE_ROUTING,
243 .me = THIS_MODULE,
244 },
245 #ifdef XT_TPROXY_HAVE_IPV6
246 {
247 .name = "TPROXY",
248 .family = NFPROTO_IPV6,
249 .table = "mangle",
250 .target = tproxy_tg6_v1,
251 .revision = 1,
252 .targetsize = sizeof(struct xt_tproxy_target_info_v1),
253 .checkentry = tproxy_tg6_check,
254 .hooks = 1 << NF_INET_PRE_ROUTING,
255 .me = THIS_MODULE,
256 },
257 #endif
258
259 };
260
tproxy_tg_init(void)261 static int __init tproxy_tg_init(void)
262 {
263 return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
264 }
265
tproxy_tg_exit(void)266 static void __exit tproxy_tg_exit(void)
267 {
268 xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
269 }
270
271 module_init(tproxy_tg_init);
272 module_exit(tproxy_tg_exit);
273 MODULE_LICENSE("GPL");
274 MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
275 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
276 MODULE_ALIAS("ipt_TPROXY");
277 MODULE_ALIAS("ip6t_TPROXY");
278