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Linux/net/netfilter/xt_TEE.c

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  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 = netdev_notifier_info_to_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 

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