xref: /linux/net/ipv6/seg6_iptunnel.c (revision 0be3ff0c) 
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  *  SR-IPv6 implementation
4  *
5  *  Author:
6  *  David Lebrun <david.lebrun@uclouvain.be>
7  */
8 
9 #include <linux/types.h>
10 #include <linux/skbuff.h>
11 #include <linux/net.h>
12 #include <linux/module.h>
13 #include <net/ip.h>
14 #include <net/ip_tunnels.h>
15 #include <net/lwtunnel.h>
16 #include <net/netevent.h>
17 #include <net/netns/generic.h>
18 #include <net/ip6_fib.h>
19 #include <net/route.h>
20 #include <net/seg6.h>
21 #include <linux/seg6.h>
22 #include <linux/seg6_iptunnel.h>
23 #include <net/addrconf.h>
24 #include <net/ip6_route.h>
25 #include <net/dst_cache.h>
26 #ifdef CONFIG_IPV6_SEG6_HMAC
27 #include <net/seg6_hmac.h>
28 #endif
29 #include <linux/netfilter.h>
30 
31 static size_t seg6_lwt_headroom(struct seg6_iptunnel_encap *tuninfo)
32 {
33 	int head = 0;
34 
35 	switch (tuninfo->mode) {
36 	case SEG6_IPTUN_MODE_INLINE:
37 		break;
38 	case SEG6_IPTUN_MODE_ENCAP:
39 		head = sizeof(struct ipv6hdr);
40 		break;
41 	case SEG6_IPTUN_MODE_L2ENCAP:
42 		return 0;
43 	}
44 
45 	return ((tuninfo->srh->hdrlen + 1) << 3) + head;
46 }
47 
48 struct seg6_lwt {
49 	struct dst_cache cache;
50 	struct seg6_iptunnel_encap tuninfo[];
51 };
52 
53 static inline struct seg6_lwt *seg6_lwt_lwtunnel(struct lwtunnel_state *lwt)
54 {
55 	return (struct seg6_lwt *)lwt->data;
56 }
57 
58 static inline struct seg6_iptunnel_encap *
59 seg6_encap_lwtunnel(struct lwtunnel_state *lwt)
60 {
61 	return seg6_lwt_lwtunnel(lwt)->tuninfo;
62 }
63 
64 static const struct nla_policy seg6_iptunnel_policy[SEG6_IPTUNNEL_MAX + 1] = {
65 	[SEG6_IPTUNNEL_SRH]	= { .type = NLA_BINARY },
66 };
67 
68 static int nla_put_srh(struct sk_buff *skb, int attrtype,
69 		       struct seg6_iptunnel_encap *tuninfo)
70 {
71 	struct seg6_iptunnel_encap *data;
72 	struct nlattr *nla;
73 	int len;
74 
75 	len = SEG6_IPTUN_ENCAP_SIZE(tuninfo);
76 
77 	nla = nla_reserve(skb, attrtype, len);
78 	if (!nla)
79 		return -EMSGSIZE;
80 
81 	data = nla_data(nla);
82 	memcpy(data, tuninfo, len);
83 
84 	return 0;
85 }
86 
87 static void set_tun_src(struct net *net, struct net_device *dev,
88 			struct in6_addr *daddr, struct in6_addr *saddr)
89 {
90 	struct seg6_pernet_data *sdata = seg6_pernet(net);
91 	struct in6_addr *tun_src;
92 
93 	rcu_read_lock();
94 
95 	tun_src = rcu_dereference(sdata->tun_src);
96 
97 	if (!ipv6_addr_any(tun_src)) {
98 		memcpy(saddr, tun_src, sizeof(struct in6_addr));
99 	} else {
100 		ipv6_dev_get_saddr(net, dev, daddr, IPV6_PREFER_SRC_PUBLIC,
101 				   saddr);
102 	}
103 
104 	rcu_read_unlock();
105 }
106 
107 /* Compute flowlabel for outer IPv6 header */
108 static __be32 seg6_make_flowlabel(struct net *net, struct sk_buff *skb,
109 				  struct ipv6hdr *inner_hdr)
110 {
111 	int do_flowlabel = net->ipv6.sysctl.seg6_flowlabel;
112 	__be32 flowlabel = 0;
113 	u32 hash;
114 
115 	if (do_flowlabel > 0) {
116 		hash = skb_get_hash(skb);
117 		hash = rol32(hash, 16);
118 		flowlabel = (__force __be32)hash & IPV6_FLOWLABEL_MASK;
119 	} else if (!do_flowlabel && skb->protocol == htons(ETH_P_IPV6)) {
120 		flowlabel = ip6_flowlabel(inner_hdr);
121 	}
122 	return flowlabel;
123 }
124 
125 /* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
126 int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
127 {
128 	struct dst_entry *dst = skb_dst(skb);
129 	struct net *net = dev_net(dst->dev);
130 	struct ipv6hdr *hdr, *inner_hdr;
131 	struct ipv6_sr_hdr *isrh;
132 	int hdrlen, tot_len, err;
133 	__be32 flowlabel;
134 
135 	hdrlen = (osrh->hdrlen + 1) << 3;
136 	tot_len = hdrlen + sizeof(*hdr);
137 
138 	err = skb_cow_head(skb, tot_len + skb->mac_len);
139 	if (unlikely(err))
140 		return err;
141 
142 	inner_hdr = ipv6_hdr(skb);
143 	flowlabel = seg6_make_flowlabel(net, skb, inner_hdr);
144 
145 	skb_push(skb, tot_len);
146 	skb_reset_network_header(skb);
147 	skb_mac_header_rebuild(skb);
148 	hdr = ipv6_hdr(skb);
149 
150 	/* inherit tc, flowlabel and hlim
151 	 * hlim will be decremented in ip6_forward() afterwards and
152 	 * decapsulation will overwrite inner hlim with outer hlim
153 	 */
154 
155 	if (skb->protocol == htons(ETH_P_IPV6)) {
156 		ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr)),
157 			     flowlabel);
158 		hdr->hop_limit = inner_hdr->hop_limit;
159 	} else {
160 		ip6_flow_hdr(hdr, 0, flowlabel);
161 		hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb));
162 
163 		memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
164 
165 		/* the control block has been erased, so we have to set the
166 		 * iif once again.
167 		 * We read the receiving interface index directly from the
168 		 * skb->skb_iif as it is done in the IPv4 receiving path (i.e.:
169 		 * ip_rcv_core(...)).
170 		 */
171 		IP6CB(skb)->iif = skb->skb_iif;
172 	}
173 
174 	hdr->nexthdr = NEXTHDR_ROUTING;
175 
176 	isrh = (void *)hdr + sizeof(*hdr);
177 	memcpy(isrh, osrh, hdrlen);
178 
179 	isrh->nexthdr = proto;
180 
181 	hdr->daddr = isrh->segments[isrh->first_segment];
182 	set_tun_src(net, dst->dev, &hdr->daddr, &hdr->saddr);
183 
184 #ifdef CONFIG_IPV6_SEG6_HMAC
185 	if (sr_has_hmac(isrh)) {
186 		err = seg6_push_hmac(net, &hdr->saddr, isrh);
187 		if (unlikely(err))
188 			return err;
189 	}
190 #endif
191 
192 	skb_postpush_rcsum(skb, hdr, tot_len);
193 
194 	return 0;
195 }
196 EXPORT_SYMBOL_GPL(seg6_do_srh_encap);
197 
198 /* insert an SRH within an IPv6 packet, just after the IPv6 header */
199 int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
200 {
201 	struct ipv6hdr *hdr, *oldhdr;
202 	struct ipv6_sr_hdr *isrh;
203 	int hdrlen, err;
204 
205 	hdrlen = (osrh->hdrlen + 1) << 3;
206 
207 	err = skb_cow_head(skb, hdrlen + skb->mac_len);
208 	if (unlikely(err))
209 		return err;
210 
211 	oldhdr = ipv6_hdr(skb);
212 
213 	skb_pull(skb, sizeof(struct ipv6hdr));
214 	skb_postpull_rcsum(skb, skb_network_header(skb),
215 			   sizeof(struct ipv6hdr));
216 
217 	skb_push(skb, sizeof(struct ipv6hdr) + hdrlen);
218 	skb_reset_network_header(skb);
219 	skb_mac_header_rebuild(skb);
220 
221 	hdr = ipv6_hdr(skb);
222 
223 	memmove(hdr, oldhdr, sizeof(*hdr));
224 
225 	isrh = (void *)hdr + sizeof(*hdr);
226 	memcpy(isrh, osrh, hdrlen);
227 
228 	isrh->nexthdr = hdr->nexthdr;
229 	hdr->nexthdr = NEXTHDR_ROUTING;
230 
231 	isrh->segments[0] = hdr->daddr;
232 	hdr->daddr = isrh->segments[isrh->first_segment];
233 
234 #ifdef CONFIG_IPV6_SEG6_HMAC
235 	if (sr_has_hmac(isrh)) {
236 		struct net *net = dev_net(skb_dst(skb)->dev);
237 
238 		err = seg6_push_hmac(net, &hdr->saddr, isrh);
239 		if (unlikely(err))
240 			return err;
241 	}
242 #endif
243 
244 	skb_postpush_rcsum(skb, hdr, sizeof(struct ipv6hdr) + hdrlen);
245 
246 	return 0;
247 }
248 EXPORT_SYMBOL_GPL(seg6_do_srh_inline);
249 
250 static int seg6_do_srh(struct sk_buff *skb)
251 {
252 	struct dst_entry *dst = skb_dst(skb);
253 	struct seg6_iptunnel_encap *tinfo;
254 	int proto, err = 0;
255 
256 	tinfo = seg6_encap_lwtunnel(dst->lwtstate);
257 
258 	switch (tinfo->mode) {
259 	case SEG6_IPTUN_MODE_INLINE:
260 		if (skb->protocol != htons(ETH_P_IPV6))
261 			return -EINVAL;
262 
263 		err = seg6_do_srh_inline(skb, tinfo->srh);
264 		if (err)
265 			return err;
266 		break;
267 	case SEG6_IPTUN_MODE_ENCAP:
268 		err = iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6);
269 		if (err)
270 			return err;
271 
272 		if (skb->protocol == htons(ETH_P_IPV6))
273 			proto = IPPROTO_IPV6;
274 		else if (skb->protocol == htons(ETH_P_IP))
275 			proto = IPPROTO_IPIP;
276 		else
277 			return -EINVAL;
278 
279 		err = seg6_do_srh_encap(skb, tinfo->srh, proto);
280 		if (err)
281 			return err;
282 
283 		skb_set_inner_transport_header(skb, skb_transport_offset(skb));
284 		skb_set_inner_protocol(skb, skb->protocol);
285 		skb->protocol = htons(ETH_P_IPV6);
286 		break;
287 	case SEG6_IPTUN_MODE_L2ENCAP:
288 		if (!skb_mac_header_was_set(skb))
289 			return -EINVAL;
290 
291 		if (pskb_expand_head(skb, skb->mac_len, 0, GFP_ATOMIC) < 0)
292 			return -ENOMEM;
293 
294 		skb_mac_header_rebuild(skb);
295 		skb_push(skb, skb->mac_len);
296 
297 		err = seg6_do_srh_encap(skb, tinfo->srh, IPPROTO_ETHERNET);
298 		if (err)
299 			return err;
300 
301 		skb->protocol = htons(ETH_P_IPV6);
302 		break;
303 	}
304 
305 	ipv6_hdr(skb)->payload_len = htons(skb->len - sizeof(struct ipv6hdr));
306 	skb_set_transport_header(skb, sizeof(struct ipv6hdr));
307 	nf_reset_ct(skb);
308 
309 	return 0;
310 }
311 
312 static int seg6_input_finish(struct net *net, struct sock *sk,
313 			     struct sk_buff *skb)
314 {
315 	return dst_input(skb);
316 }
317 
318 static int seg6_input_core(struct net *net, struct sock *sk,
319 			   struct sk_buff *skb)
320 {
321 	struct dst_entry *orig_dst = skb_dst(skb);
322 	struct dst_entry *dst = NULL;
323 	struct seg6_lwt *slwt;
324 	int err;
325 
326 	err = seg6_do_srh(skb);
327 	if (unlikely(err)) {
328 		kfree_skb(skb);
329 		return err;
330 	}
331 
332 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
333 
334 	preempt_disable();
335 	dst = dst_cache_get(&slwt->cache);
336 	preempt_enable();
337 
338 	skb_dst_drop(skb);
339 
340 	if (!dst) {
341 		ip6_route_input(skb);
342 		dst = skb_dst(skb);
343 		if (!dst->error) {
344 			preempt_disable();
345 			dst_cache_set_ip6(&slwt->cache, dst,
346 					  &ipv6_hdr(skb)->saddr);
347 			preempt_enable();
348 		}
349 	} else {
350 		skb_dst_set(skb, dst);
351 	}
352 
353 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
354 	if (unlikely(err))
355 		return err;
356 
357 	if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
358 		return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
359 			       dev_net(skb->dev), NULL, skb, NULL,
360 			       skb_dst(skb)->dev, seg6_input_finish);
361 
362 	return seg6_input_finish(dev_net(skb->dev), NULL, skb);
363 }
364 
365 static int seg6_input_nf(struct sk_buff *skb)
366 {
367 	struct net_device *dev = skb_dst(skb)->dev;
368 	struct net *net = dev_net(skb->dev);
369 
370 	switch (skb->protocol) {
371 	case htons(ETH_P_IP):
372 		return NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING, net, NULL,
373 			       skb, NULL, dev, seg6_input_core);
374 	case htons(ETH_P_IPV6):
375 		return NF_HOOK(NFPROTO_IPV6, NF_INET_POST_ROUTING, net, NULL,
376 			       skb, NULL, dev, seg6_input_core);
377 	}
378 
379 	return -EINVAL;
380 }
381 
382 static int seg6_input(struct sk_buff *skb)
383 {
384 	if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
385 		return seg6_input_nf(skb);
386 
387 	return seg6_input_core(dev_net(skb->dev), NULL, skb);
388 }
389 
390 static int seg6_output_core(struct net *net, struct sock *sk,
391 			    struct sk_buff *skb)
392 {
393 	struct dst_entry *orig_dst = skb_dst(skb);
394 	struct dst_entry *dst = NULL;
395 	struct seg6_lwt *slwt;
396 	int err;
397 
398 	err = seg6_do_srh(skb);
399 	if (unlikely(err))
400 		goto drop;
401 
402 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
403 
404 	preempt_disable();
405 	dst = dst_cache_get(&slwt->cache);
406 	preempt_enable();
407 
408 	if (unlikely(!dst)) {
409 		struct ipv6hdr *hdr = ipv6_hdr(skb);
410 		struct flowi6 fl6;
411 
412 		memset(&fl6, 0, sizeof(fl6));
413 		fl6.daddr = hdr->daddr;
414 		fl6.saddr = hdr->saddr;
415 		fl6.flowlabel = ip6_flowinfo(hdr);
416 		fl6.flowi6_mark = skb->mark;
417 		fl6.flowi6_proto = hdr->nexthdr;
418 
419 		dst = ip6_route_output(net, NULL, &fl6);
420 		if (dst->error) {
421 			err = dst->error;
422 			dst_release(dst);
423 			goto drop;
424 		}
425 
426 		preempt_disable();
427 		dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
428 		preempt_enable();
429 	}
430 
431 	skb_dst_drop(skb);
432 	skb_dst_set(skb, dst);
433 
434 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
435 	if (unlikely(err))
436 		goto drop;
437 
438 	if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
439 		return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, net, sk, skb,
440 			       NULL, skb_dst(skb)->dev, dst_output);
441 
442 	return dst_output(net, sk, skb);
443 drop:
444 	kfree_skb(skb);
445 	return err;
446 }
447 
448 static int seg6_output_nf(struct net *net, struct sock *sk, struct sk_buff *skb)
449 {
450 	struct net_device *dev = skb_dst(skb)->dev;
451 
452 	switch (skb->protocol) {
453 	case htons(ETH_P_IP):
454 		return NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING, net, sk, skb,
455 			       NULL, dev, seg6_output_core);
456 	case htons(ETH_P_IPV6):
457 		return NF_HOOK(NFPROTO_IPV6, NF_INET_POST_ROUTING, net, sk, skb,
458 			       NULL, dev, seg6_output_core);
459 	}
460 
461 	return -EINVAL;
462 }
463 
464 static int seg6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
465 {
466 	if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
467 		return seg6_output_nf(net, sk, skb);
468 
469 	return seg6_output_core(net, sk, skb);
470 }
471 
472 static int seg6_build_state(struct net *net, struct nlattr *nla,
473 			    unsigned int family, const void *cfg,
474 			    struct lwtunnel_state **ts,
475 			    struct netlink_ext_ack *extack)
476 {
477 	struct nlattr *tb[SEG6_IPTUNNEL_MAX + 1];
478 	struct seg6_iptunnel_encap *tuninfo;
479 	struct lwtunnel_state *newts;
480 	int tuninfo_len, min_size;
481 	struct seg6_lwt *slwt;
482 	int err;
483 
484 	if (family != AF_INET && family != AF_INET6)
485 		return -EINVAL;
486 
487 	err = nla_parse_nested_deprecated(tb, SEG6_IPTUNNEL_MAX, nla,
488 					  seg6_iptunnel_policy, extack);
489 
490 	if (err < 0)
491 		return err;
492 
493 	if (!tb[SEG6_IPTUNNEL_SRH])
494 		return -EINVAL;
495 
496 	tuninfo = nla_data(tb[SEG6_IPTUNNEL_SRH]);
497 	tuninfo_len = nla_len(tb[SEG6_IPTUNNEL_SRH]);
498 
499 	/* tuninfo must contain at least the iptunnel encap structure,
500 	 * the SRH and one segment
501 	 */
502 	min_size = sizeof(*tuninfo) + sizeof(struct ipv6_sr_hdr) +
503 		   sizeof(struct in6_addr);
504 	if (tuninfo_len < min_size)
505 		return -EINVAL;
506 
507 	switch (tuninfo->mode) {
508 	case SEG6_IPTUN_MODE_INLINE:
509 		if (family != AF_INET6)
510 			return -EINVAL;
511 
512 		break;
513 	case SEG6_IPTUN_MODE_ENCAP:
514 		break;
515 	case SEG6_IPTUN_MODE_L2ENCAP:
516 		break;
517 	default:
518 		return -EINVAL;
519 	}
520 
521 	/* verify that SRH is consistent */
522 	if (!seg6_validate_srh(tuninfo->srh, tuninfo_len - sizeof(*tuninfo), false))
523 		return -EINVAL;
524 
525 	newts = lwtunnel_state_alloc(tuninfo_len + sizeof(*slwt));
526 	if (!newts)
527 		return -ENOMEM;
528 
529 	slwt = seg6_lwt_lwtunnel(newts);
530 
531 	err = dst_cache_init(&slwt->cache, GFP_ATOMIC);
532 	if (err) {
533 		kfree(newts);
534 		return err;
535 	}
536 
537 	memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);
538 
539 	newts->type = LWTUNNEL_ENCAP_SEG6;
540 	newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
541 
542 	if (tuninfo->mode != SEG6_IPTUN_MODE_L2ENCAP)
543 		newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
544 
545 	newts->headroom = seg6_lwt_headroom(tuninfo);
546 
547 	*ts = newts;
548 
549 	return 0;
550 }
551 
552 static void seg6_destroy_state(struct lwtunnel_state *lwt)
553 {
554 	dst_cache_destroy(&seg6_lwt_lwtunnel(lwt)->cache);
555 }
556 
557 static int seg6_fill_encap_info(struct sk_buff *skb,
558 				struct lwtunnel_state *lwtstate)
559 {
560 	struct seg6_iptunnel_encap *tuninfo = seg6_encap_lwtunnel(lwtstate);
561 
562 	if (nla_put_srh(skb, SEG6_IPTUNNEL_SRH, tuninfo))
563 		return -EMSGSIZE;
564 
565 	return 0;
566 }
567 
568 static int seg6_encap_nlsize(struct lwtunnel_state *lwtstate)
569 {
570 	struct seg6_iptunnel_encap *tuninfo = seg6_encap_lwtunnel(lwtstate);
571 
572 	return nla_total_size(SEG6_IPTUN_ENCAP_SIZE(tuninfo));
573 }
574 
575 static int seg6_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
576 {
577 	struct seg6_iptunnel_encap *a_hdr = seg6_encap_lwtunnel(a);
578 	struct seg6_iptunnel_encap *b_hdr = seg6_encap_lwtunnel(b);
579 	int len = SEG6_IPTUN_ENCAP_SIZE(a_hdr);
580 
581 	if (len != SEG6_IPTUN_ENCAP_SIZE(b_hdr))
582 		return 1;
583 
584 	return memcmp(a_hdr, b_hdr, len);
585 }
586 
587 static const struct lwtunnel_encap_ops seg6_iptun_ops = {
588 	.build_state = seg6_build_state,
589 	.destroy_state = seg6_destroy_state,
590 	.output = seg6_output,
591 	.input = seg6_input,
592 	.fill_encap = seg6_fill_encap_info,
593 	.get_encap_size = seg6_encap_nlsize,
594 	.cmp_encap = seg6_encap_cmp,
595 	.owner = THIS_MODULE,
596 };
597 
598 int __init seg6_iptunnel_init(void)
599 {
600 	return lwtunnel_encap_add_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
601 }
602 
603 void seg6_iptunnel_exit(void)
604 {
605 	lwtunnel_encap_del_ops(&seg6_iptun_ops, LWTUNNEL_ENCAP_SEG6);
606 }
607