xref: /openbmc/linux/net/netfilter/xt_TEE.c (revision d0b73b48) 
1 /*
2  *	"TEE" target extension for Xtables
3  *	Copyright © Sebastian Claßen, 2007
4  *	Jan Engelhardt, 2007-2010
5  *
6  *	based on ipt_ROUTE.c from Cédric de Launois
7  *	<delaunois@info.ucl.be>
8  *
9  *	This program is free software; you can redistribute it and/or
10  *	modify it under the terms of the GNU General Public License
11  *	version 2 or later, as published by the Free Software Foundation.
12  */
13 #include <linux/ip.h>
14 #include <linux/module.h>
15 #include <linux/percpu.h>
16 #include <linux/route.h>
17 #include <linux/skbuff.h>
18 #include <linux/notifier.h>
19 #include <net/checksum.h>
20 #include <net/icmp.h>
21 #include <net/ip.h>
22 #include <net/ipv6.h>
23 #include <net/ip6_route.h>
24 #include <net/route.h>
25 #include <linux/netfilter/x_tables.h>
26 #include <linux/netfilter/xt_TEE.h>
27 
28 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
29 #	define WITH_CONNTRACK 1
30 #	include <net/netfilter/nf_conntrack.h>
31 #endif
32 
33 struct xt_tee_priv {
34 	struct notifier_block	notifier;
35 	struct xt_tee_tginfo	*tginfo;
36 	int			oif;
37 };
38 
39 static const union nf_inet_addr tee_zero_address;
40 static DEFINE_PER_CPU(bool, tee_active);
41 
42 static struct net *pick_net(struct sk_buff *skb)
43 {
44 #ifdef CONFIG_NET_NS
45 	const struct dst_entry *dst;
46 
47 	if (skb->dev != NULL)
48 		return dev_net(skb->dev);
49 	dst = skb_dst(skb);
50 	if (dst != NULL && dst->dev != NULL)
51 		return dev_net(dst->dev);
52 #endif
53 	return &init_net;
54 }
55 
56 static bool
57 tee_tg_route4(struct sk_buff *skb, const struct xt_tee_tginfo *info)
58 {
59 	const struct iphdr *iph = ip_hdr(skb);
60 	struct net *net = pick_net(skb);
61 	struct rtable *rt;
62 	struct flowi4 fl4;
63 
64 	memset(&fl4, 0, sizeof(fl4));
65 	if (info->priv) {
66 		if (info->priv->oif == -1)
67 			return false;
68 		fl4.flowi4_oif = info->priv->oif;
69 	}
70 	fl4.daddr = info->gw.ip;
71 	fl4.flowi4_tos = RT_TOS(iph->tos);
72 	fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
73 	fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
74 	rt = ip_route_output_key(net, &fl4);
75 	if (IS_ERR(rt))
76 		return false;
77 
78 	skb_dst_drop(skb);
79 	skb_dst_set(skb, &rt->dst);
80 	skb->dev      = rt->dst.dev;
81 	skb->protocol = htons(ETH_P_IP);
82 	return true;
83 }
84 
85 static unsigned int
86 tee_tg4(struct sk_buff *skb, const struct xt_action_param *par)
87 {
88 	const struct xt_tee_tginfo *info = par->targinfo;
89 	struct iphdr *iph;
90 
91 	if (__this_cpu_read(tee_active))
92 		return XT_CONTINUE;
93 	/*
94 	 * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
95 	 * the original skb, which should continue on its way as if nothing has
96 	 * happened. The copy should be independently delivered to the TEE
97 	 * --gateway.
98 	 */
99 	skb = pskb_copy(skb, GFP_ATOMIC);
100 	if (skb == NULL)
101 		return XT_CONTINUE;
102 
103 #ifdef WITH_CONNTRACK
104 	/* Avoid counting cloned packets towards the original connection. */
105 	nf_conntrack_put(skb->nfct);
106 	skb->nfct     = &nf_ct_untracked_get()->ct_general;
107 	skb->nfctinfo = IP_CT_NEW;
108 	nf_conntrack_get(skb->nfct);
109 #endif
110 	/*
111 	 * If we are in PREROUTING/INPUT, the checksum must be recalculated
112 	 * since the length could have changed as a result of defragmentation.
113 	 *
114 	 * We also decrease the TTL to mitigate potential TEE loops
115 	 * between two hosts.
116 	 *
117 	 * Set %IP_DF so that the original source is notified of a potentially
118 	 * decreased MTU on the clone route. IPv6 does this too.
119 	 */
120 	iph = ip_hdr(skb);
121 	iph->frag_off |= htons(IP_DF);
122 	if (par->hooknum == NF_INET_PRE_ROUTING ||
123 	    par->hooknum == NF_INET_LOCAL_IN)
124 		--iph->ttl;
125 	ip_send_check(iph);
126 
127 	if (tee_tg_route4(skb, info)) {
128 		__this_cpu_write(tee_active, true);
129 		ip_local_out(skb);
130 		__this_cpu_write(tee_active, false);
131 	} else {
132 		kfree_skb(skb);
133 	}
134 	return XT_CONTINUE;
135 }
136 
137 #if IS_ENABLED(CONFIG_IPV6)
138 static bool
139 tee_tg_route6(struct sk_buff *skb, const struct xt_tee_tginfo *info)
140 {
141 	const struct ipv6hdr *iph = ipv6_hdr(skb);
142 	struct net *net = pick_net(skb);
143 	struct dst_entry *dst;
144 	struct flowi6 fl6;
145 
146 	memset(&fl6, 0, sizeof(fl6));
147 	if (info->priv) {
148 		if (info->priv->oif == -1)
149 			return false;
150 		fl6.flowi6_oif = info->priv->oif;
151 	}
152 	fl6.daddr = info->gw.in6;
153 	fl6.flowlabel = ((iph->flow_lbl[0] & 0xF) << 16) |
154 			   (iph->flow_lbl[1] << 8) | iph->flow_lbl[2];
155 	dst = ip6_route_output(net, NULL, &fl6);
156 	if (dst->error) {
157 		dst_release(dst);
158 		return false;
159 	}
160 	skb_dst_drop(skb);
161 	skb_dst_set(skb, dst);
162 	skb->dev      = dst->dev;
163 	skb->protocol = htons(ETH_P_IPV6);
164 	return true;
165 }
166 
167 static unsigned int
168 tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
169 {
170 	const struct xt_tee_tginfo *info = par->targinfo;
171 
172 	if (__this_cpu_read(tee_active))
173 		return XT_CONTINUE;
174 	skb = pskb_copy(skb, GFP_ATOMIC);
175 	if (skb == NULL)
176 		return XT_CONTINUE;
177 
178 #ifdef WITH_CONNTRACK
179 	nf_conntrack_put(skb->nfct);
180 	skb->nfct     = &nf_ct_untracked_get()->ct_general;
181 	skb->nfctinfo = IP_CT_NEW;
182 	nf_conntrack_get(skb->nfct);
183 #endif
184 	if (par->hooknum == NF_INET_PRE_ROUTING ||
185 	    par->hooknum == NF_INET_LOCAL_IN) {
186 		struct ipv6hdr *iph = ipv6_hdr(skb);
187 		--iph->hop_limit;
188 	}
189 	if (tee_tg_route6(skb, info)) {
190 		__this_cpu_write(tee_active, true);
191 		ip6_local_out(skb);
192 		__this_cpu_write(tee_active, false);
193 	} else {
194 		kfree_skb(skb);
195 	}
196 	return XT_CONTINUE;
197 }
198 #endif
199 
200 static int tee_netdev_event(struct notifier_block *this, unsigned long event,
201 			    void *ptr)
202 {
203 	struct net_device *dev = ptr;
204 	struct xt_tee_priv *priv;
205 
206 	priv = container_of(this, struct xt_tee_priv, notifier);
207 	switch (event) {
208 	case NETDEV_REGISTER:
209 		if (!strcmp(dev->name, priv->tginfo->oif))
210 			priv->oif = dev->ifindex;
211 		break;
212 	case NETDEV_UNREGISTER:
213 		if (dev->ifindex == priv->oif)
214 			priv->oif = -1;
215 		break;
216 	case NETDEV_CHANGENAME:
217 		if (!strcmp(dev->name, priv->tginfo->oif))
218 			priv->oif = dev->ifindex;
219 		else if (dev->ifindex == priv->oif)
220 			priv->oif = -1;
221 		break;
222 	}
223 
224 	return NOTIFY_DONE;
225 }
226 
227 static int tee_tg_check(const struct xt_tgchk_param *par)
228 {
229 	struct xt_tee_tginfo *info = par->targinfo;
230 	struct xt_tee_priv *priv;
231 
232 	/* 0.0.0.0 and :: not allowed */
233 	if (memcmp(&info->gw, &tee_zero_address,
234 		   sizeof(tee_zero_address)) == 0)
235 		return -EINVAL;
236 
237 	if (info->oif[0]) {
238 		if (info->oif[sizeof(info->oif)-1] != '\0')
239 			return -EINVAL;
240 
241 		priv = kzalloc(sizeof(*priv), GFP_KERNEL);
242 		if (priv == NULL)
243 			return -ENOMEM;
244 
245 		priv->tginfo  = info;
246 		priv->oif     = -1;
247 		priv->notifier.notifier_call = tee_netdev_event;
248 		info->priv    = priv;
249 
250 		register_netdevice_notifier(&priv->notifier);
251 	} else
252 		info->priv = NULL;
253 
254 	return 0;
255 }
256 
257 static void tee_tg_destroy(const struct xt_tgdtor_param *par)
258 {
259 	struct xt_tee_tginfo *info = par->targinfo;
260 
261 	if (info->priv) {
262 		unregister_netdevice_notifier(&info->priv->notifier);
263 		kfree(info->priv);
264 	}
265 }
266 
267 static struct xt_target tee_tg_reg[] __read_mostly = {
268 	{
269 		.name       = "TEE",
270 		.revision   = 1,
271 		.family     = NFPROTO_IPV4,
272 		.target     = tee_tg4,
273 		.targetsize = sizeof(struct xt_tee_tginfo),
274 		.checkentry = tee_tg_check,
275 		.destroy    = tee_tg_destroy,
276 		.me         = THIS_MODULE,
277 	},
278 #if IS_ENABLED(CONFIG_IPV6)
279 	{
280 		.name       = "TEE",
281 		.revision   = 1,
282 		.family     = NFPROTO_IPV6,
283 		.target     = tee_tg6,
284 		.targetsize = sizeof(struct xt_tee_tginfo),
285 		.checkentry = tee_tg_check,
286 		.destroy    = tee_tg_destroy,
287 		.me         = THIS_MODULE,
288 	},
289 #endif
290 };
291 
292 static int __init tee_tg_init(void)
293 {
294 	return xt_register_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
295 }
296 
297 static void __exit tee_tg_exit(void)
298 {
299 	xt_unregister_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
300 }
301 
302 module_init(tee_tg_init);
303 module_exit(tee_tg_exit);
304 MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
305 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
306 MODULE_DESCRIPTION("Xtables: Reroute packet copy");
307 MODULE_LICENSE("GPL");
308 MODULE_ALIAS("ipt_TEE");
309 MODULE_ALIAS("ip6t_TEE");
310