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Linux/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c

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  1 /*
  2  * (C) 1999-2001 Paul `Rusty' Russell
  3  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
  4  * (C) 2011 Patrick McHardy <kaber@trash.net>
  5  *
  6  * This program is free software; you can redistribute it and/or modify
  7  * it under the terms of the GNU General Public License version 2 as
  8  * published by the Free Software Foundation.
  9  */
 10 
 11 #include <linux/types.h>
 12 #include <linux/module.h>
 13 #include <linux/skbuff.h>
 14 #include <linux/ip.h>
 15 #include <linux/icmp.h>
 16 #include <linux/netfilter.h>
 17 #include <linux/netfilter_ipv4.h>
 18 #include <net/secure_seq.h>
 19 #include <net/checksum.h>
 20 #include <net/route.h>
 21 #include <net/ip.h>
 22 
 23 #include <net/netfilter/nf_conntrack_core.h>
 24 #include <net/netfilter/nf_conntrack.h>
 25 #include <net/netfilter/nf_nat_core.h>
 26 #include <net/netfilter/nf_nat_l3proto.h>
 27 #include <net/netfilter/nf_nat_l4proto.h>
 28 
 29 static const struct nf_nat_l3proto nf_nat_l3proto_ipv4;
 30 
 31 #ifdef CONFIG_XFRM
 32 static void nf_nat_ipv4_decode_session(struct sk_buff *skb,
 33                                        const struct nf_conn *ct,
 34                                        enum ip_conntrack_dir dir,
 35                                        unsigned long statusbit,
 36                                        struct flowi *fl)
 37 {
 38         const struct nf_conntrack_tuple *t = &ct->tuplehash[dir].tuple;
 39         struct flowi4 *fl4 = &fl->u.ip4;
 40 
 41         if (ct->status & statusbit) {
 42                 fl4->daddr = t->dst.u3.ip;
 43                 if (t->dst.protonum == IPPROTO_TCP ||
 44                     t->dst.protonum == IPPROTO_UDP ||
 45                     t->dst.protonum == IPPROTO_UDPLITE ||
 46                     t->dst.protonum == IPPROTO_DCCP ||
 47                     t->dst.protonum == IPPROTO_SCTP)
 48                         fl4->fl4_dport = t->dst.u.all;
 49         }
 50 
 51         statusbit ^= IPS_NAT_MASK;
 52 
 53         if (ct->status & statusbit) {
 54                 fl4->saddr = t->src.u3.ip;
 55                 if (t->dst.protonum == IPPROTO_TCP ||
 56                     t->dst.protonum == IPPROTO_UDP ||
 57                     t->dst.protonum == IPPROTO_UDPLITE ||
 58                     t->dst.protonum == IPPROTO_DCCP ||
 59                     t->dst.protonum == IPPROTO_SCTP)
 60                         fl4->fl4_sport = t->src.u.all;
 61         }
 62 }
 63 #endif /* CONFIG_XFRM */
 64 
 65 static bool nf_nat_ipv4_in_range(const struct nf_conntrack_tuple *t,
 66                                  const struct nf_nat_range2 *range)
 67 {
 68         return ntohl(t->src.u3.ip) >= ntohl(range->min_addr.ip) &&
 69                ntohl(t->src.u3.ip) <= ntohl(range->max_addr.ip);
 70 }
 71 
 72 static u32 nf_nat_ipv4_secure_port(const struct nf_conntrack_tuple *t,
 73                                    __be16 dport)
 74 {
 75         return secure_ipv4_port_ephemeral(t->src.u3.ip, t->dst.u3.ip, dport);
 76 }
 77 
 78 static bool nf_nat_ipv4_manip_pkt(struct sk_buff *skb,
 79                                   unsigned int iphdroff,
 80                                   const struct nf_nat_l4proto *l4proto,
 81                                   const struct nf_conntrack_tuple *target,
 82                                   enum nf_nat_manip_type maniptype)
 83 {
 84         struct iphdr *iph;
 85         unsigned int hdroff;
 86 
 87         if (!skb_make_writable(skb, iphdroff + sizeof(*iph)))
 88                 return false;
 89 
 90         iph = (void *)skb->data + iphdroff;
 91         hdroff = iphdroff + iph->ihl * 4;
 92 
 93         if (!l4proto->manip_pkt(skb, &nf_nat_l3proto_ipv4, iphdroff, hdroff,
 94                                 target, maniptype))
 95                 return false;
 96         iph = (void *)skb->data + iphdroff;
 97 
 98         if (maniptype == NF_NAT_MANIP_SRC) {
 99                 csum_replace4(&iph->check, iph->saddr, target->src.u3.ip);
100                 iph->saddr = target->src.u3.ip;
101         } else {
102                 csum_replace4(&iph->check, iph->daddr, target->dst.u3.ip);
103                 iph->daddr = target->dst.u3.ip;
104         }
105         return true;
106 }
107 
108 static void nf_nat_ipv4_csum_update(struct sk_buff *skb,
109                                     unsigned int iphdroff, __sum16 *check,
110                                     const struct nf_conntrack_tuple *t,
111                                     enum nf_nat_manip_type maniptype)
112 {
113         struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
114         __be32 oldip, newip;
115 
116         if (maniptype == NF_NAT_MANIP_SRC) {
117                 oldip = iph->saddr;
118                 newip = t->src.u3.ip;
119         } else {
120                 oldip = iph->daddr;
121                 newip = t->dst.u3.ip;
122         }
123         inet_proto_csum_replace4(check, skb, oldip, newip, true);
124 }
125 
126 static void nf_nat_ipv4_csum_recalc(struct sk_buff *skb,
127                                     u8 proto, void *data, __sum16 *check,
128                                     int datalen, int oldlen)
129 {
130         if (skb->ip_summed != CHECKSUM_PARTIAL) {
131                 const struct iphdr *iph = ip_hdr(skb);
132 
133                 skb->ip_summed = CHECKSUM_PARTIAL;
134                 skb->csum_start = skb_headroom(skb) + skb_network_offset(skb) +
135                         ip_hdrlen(skb);
136                 skb->csum_offset = (void *)check - data;
137                 *check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, datalen,
138                                             proto, 0);
139         } else
140                 inet_proto_csum_replace2(check, skb,
141                                          htons(oldlen), htons(datalen), true);
142 }
143 
144 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
145 static int nf_nat_ipv4_nlattr_to_range(struct nlattr *tb[],
146                                        struct nf_nat_range2 *range)
147 {
148         if (tb[CTA_NAT_V4_MINIP]) {
149                 range->min_addr.ip = nla_get_be32(tb[CTA_NAT_V4_MINIP]);
150                 range->flags |= NF_NAT_RANGE_MAP_IPS;
151         }
152 
153         if (tb[CTA_NAT_V4_MAXIP])
154                 range->max_addr.ip = nla_get_be32(tb[CTA_NAT_V4_MAXIP]);
155         else
156                 range->max_addr.ip = range->min_addr.ip;
157 
158         return 0;
159 }
160 #endif
161 
162 static const struct nf_nat_l3proto nf_nat_l3proto_ipv4 = {
163         .l3proto                = NFPROTO_IPV4,
164         .in_range               = nf_nat_ipv4_in_range,
165         .secure_port            = nf_nat_ipv4_secure_port,
166         .manip_pkt              = nf_nat_ipv4_manip_pkt,
167         .csum_update            = nf_nat_ipv4_csum_update,
168         .csum_recalc            = nf_nat_ipv4_csum_recalc,
169 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
170         .nlattr_to_range        = nf_nat_ipv4_nlattr_to_range,
171 #endif
172 #ifdef CONFIG_XFRM
173         .decode_session         = nf_nat_ipv4_decode_session,
174 #endif
175 };
176 
177 int nf_nat_icmp_reply_translation(struct sk_buff *skb,
178                                   struct nf_conn *ct,
179                                   enum ip_conntrack_info ctinfo,
180                                   unsigned int hooknum)
181 {
182         struct {
183                 struct icmphdr  icmp;
184                 struct iphdr    ip;
185         } *inside;
186         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
187         enum nf_nat_manip_type manip = HOOK2MANIP(hooknum);
188         unsigned int hdrlen = ip_hdrlen(skb);
189         const struct nf_nat_l4proto *l4proto;
190         struct nf_conntrack_tuple target;
191         unsigned long statusbit;
192 
193         WARN_ON(ctinfo != IP_CT_RELATED && ctinfo != IP_CT_RELATED_REPLY);
194 
195         if (!skb_make_writable(skb, hdrlen + sizeof(*inside)))
196                 return 0;
197         if (nf_ip_checksum(skb, hooknum, hdrlen, 0))
198                 return 0;
199 
200         inside = (void *)skb->data + hdrlen;
201         if (inside->icmp.type == ICMP_REDIRECT) {
202                 if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
203                         return 0;
204                 if (ct->status & IPS_NAT_MASK)
205                         return 0;
206         }
207 
208         if (manip == NF_NAT_MANIP_SRC)
209                 statusbit = IPS_SRC_NAT;
210         else
211                 statusbit = IPS_DST_NAT;
212 
213         /* Invert if this is reply direction */
214         if (dir == IP_CT_DIR_REPLY)
215                 statusbit ^= IPS_NAT_MASK;
216 
217         if (!(ct->status & statusbit))
218                 return 1;
219 
220         l4proto = __nf_nat_l4proto_find(NFPROTO_IPV4, inside->ip.protocol);
221         if (!nf_nat_ipv4_manip_pkt(skb, hdrlen + sizeof(inside->icmp),
222                                    l4proto, &ct->tuplehash[!dir].tuple, !manip))
223                 return 0;
224 
225         if (skb->ip_summed != CHECKSUM_PARTIAL) {
226                 /* Reloading "inside" here since manip_pkt may reallocate */
227                 inside = (void *)skb->data + hdrlen;
228                 inside->icmp.checksum = 0;
229                 inside->icmp.checksum =
230                         csum_fold(skb_checksum(skb, hdrlen,
231                                                skb->len - hdrlen, 0));
232         }
233 
234         /* Change outer to look like the reply to an incoming packet */
235         nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
236         l4proto = __nf_nat_l4proto_find(NFPROTO_IPV4, 0);
237         if (!nf_nat_ipv4_manip_pkt(skb, 0, l4proto, &target, manip))
238                 return 0;
239 
240         return 1;
241 }
242 EXPORT_SYMBOL_GPL(nf_nat_icmp_reply_translation);
243 
244 static unsigned int
245 nf_nat_ipv4_fn(void *priv, struct sk_buff *skb,
246                const struct nf_hook_state *state)
247 {
248         struct nf_conn *ct;
249         enum ip_conntrack_info ctinfo;
250 
251         ct = nf_ct_get(skb, &ctinfo);
252         if (!ct)
253                 return NF_ACCEPT;
254 
255         if (ctinfo == IP_CT_RELATED || ctinfo == IP_CT_RELATED_REPLY) {
256                 if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
257                         if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
258                                                            state->hook))
259                                 return NF_DROP;
260                         else
261                                 return NF_ACCEPT;
262                 }
263         }
264 
265         return nf_nat_inet_fn(priv, skb, state);
266 }
267 
268 static unsigned int
269 nf_nat_ipv4_in(void *priv, struct sk_buff *skb,
270                const struct nf_hook_state *state)
271 {
272         unsigned int ret;
273         __be32 daddr = ip_hdr(skb)->daddr;
274 
275         ret = nf_nat_ipv4_fn(priv, skb, state);
276         if (ret != NF_DROP && ret != NF_STOLEN &&
277             daddr != ip_hdr(skb)->daddr)
278                 skb_dst_drop(skb);
279 
280         return ret;
281 }
282 
283 static unsigned int
284 nf_nat_ipv4_out(void *priv, struct sk_buff *skb,
285                 const struct nf_hook_state *state)
286 {
287 #ifdef CONFIG_XFRM
288         const struct nf_conn *ct;
289         enum ip_conntrack_info ctinfo;
290         int err;
291 #endif
292         unsigned int ret;
293 
294         ret = nf_nat_ipv4_fn(priv, skb, state);
295 #ifdef CONFIG_XFRM
296         if (ret != NF_DROP && ret != NF_STOLEN &&
297             !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
298             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
299                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
300 
301                 if ((ct->tuplehash[dir].tuple.src.u3.ip !=
302                      ct->tuplehash[!dir].tuple.dst.u3.ip) ||
303                     (ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
304                      ct->tuplehash[dir].tuple.src.u.all !=
305                      ct->tuplehash[!dir].tuple.dst.u.all)) {
306                         err = nf_xfrm_me_harder(state->net, skb, AF_INET);
307                         if (err < 0)
308                                 ret = NF_DROP_ERR(err);
309                 }
310         }
311 #endif
312         return ret;
313 }
314 
315 static unsigned int
316 nf_nat_ipv4_local_fn(void *priv, struct sk_buff *skb,
317                      const struct nf_hook_state *state)
318 {
319         const struct nf_conn *ct;
320         enum ip_conntrack_info ctinfo;
321         unsigned int ret;
322         int err;
323 
324         ret = nf_nat_ipv4_fn(priv, skb, state);
325         if (ret != NF_DROP && ret != NF_STOLEN &&
326             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
327                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
328 
329                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
330                     ct->tuplehash[!dir].tuple.src.u3.ip) {
331                         err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
332                         if (err < 0)
333                                 ret = NF_DROP_ERR(err);
334                 }
335 #ifdef CONFIG_XFRM
336                 else if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
337                          ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
338                          ct->tuplehash[dir].tuple.dst.u.all !=
339                          ct->tuplehash[!dir].tuple.src.u.all) {
340                         err = nf_xfrm_me_harder(state->net, skb, AF_INET);
341                         if (err < 0)
342                                 ret = NF_DROP_ERR(err);
343                 }
344 #endif
345         }
346         return ret;
347 }
348 
349 static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
350         /* Before packet filtering, change destination */
351         {
352                 .hook           = nf_nat_ipv4_in,
353                 .pf             = NFPROTO_IPV4,
354                 .hooknum        = NF_INET_PRE_ROUTING,
355                 .priority       = NF_IP_PRI_NAT_DST,
356         },
357         /* After packet filtering, change source */
358         {
359                 .hook           = nf_nat_ipv4_out,
360                 .pf             = NFPROTO_IPV4,
361                 .hooknum        = NF_INET_POST_ROUTING,
362                 .priority       = NF_IP_PRI_NAT_SRC,
363         },
364         /* Before packet filtering, change destination */
365         {
366                 .hook           = nf_nat_ipv4_local_fn,
367                 .pf             = NFPROTO_IPV4,
368                 .hooknum        = NF_INET_LOCAL_OUT,
369                 .priority       = NF_IP_PRI_NAT_DST,
370         },
371         /* After packet filtering, change source */
372         {
373                 .hook           = nf_nat_ipv4_fn,
374                 .pf             = NFPROTO_IPV4,
375                 .hooknum        = NF_INET_LOCAL_IN,
376                 .priority       = NF_IP_PRI_NAT_SRC,
377         },
378 };
379 
380 int nf_nat_l3proto_ipv4_register_fn(struct net *net, const struct nf_hook_ops *ops)
381 {
382         return nf_nat_register_fn(net, ops, nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
383 }
384 EXPORT_SYMBOL_GPL(nf_nat_l3proto_ipv4_register_fn);
385 
386 void nf_nat_l3proto_ipv4_unregister_fn(struct net *net, const struct nf_hook_ops *ops)
387 {
388         nf_nat_unregister_fn(net, ops, ARRAY_SIZE(nf_nat_ipv4_ops));
389 }
390 EXPORT_SYMBOL_GPL(nf_nat_l3proto_ipv4_unregister_fn);
391 
392 static int __init nf_nat_l3proto_ipv4_init(void)
393 {
394         int err;
395 
396         err = nf_nat_l4proto_register(NFPROTO_IPV4, &nf_nat_l4proto_icmp);
397         if (err < 0)
398                 goto err1;
399         err = nf_nat_l3proto_register(&nf_nat_l3proto_ipv4);
400         if (err < 0)
401                 goto err2;
402         return err;
403 
404 err2:
405         nf_nat_l4proto_unregister(NFPROTO_IPV4, &nf_nat_l4proto_icmp);
406 err1:
407         return err;
408 }
409 
410 static void __exit nf_nat_l3proto_ipv4_exit(void)
411 {
412         nf_nat_l3proto_unregister(&nf_nat_l3proto_ipv4);
413         nf_nat_l4proto_unregister(NFPROTO_IPV4, &nf_nat_l4proto_icmp);
414 }
415 
416 MODULE_LICENSE("GPL");
417 MODULE_ALIAS("nf-nat-" __stringify(AF_INET));
418 
419 module_init(nf_nat_l3proto_ipv4_init);
420 module_exit(nf_nat_l3proto_ipv4_exit);
421 

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