1 // SPDX-License-Identifier: GPL-2.0
2 
3 /* In-place tunneling */
4 
5 #include <stdbool.h>
6 #include <string.h>
7 
8 #include <linux/stddef.h>
9 #include <linux/bpf.h>
10 #include <linux/if_ether.h>
11 #include <linux/in.h>
12 #include <linux/ip.h>
13 #include <linux/ipv6.h>
14 #include <linux/mpls.h>
15 #include <linux/tcp.h>
16 #include <linux/udp.h>
17 #include <linux/pkt_cls.h>
18 #include <linux/types.h>
19 
20 #include <bpf/bpf_endian.h>
21 #include <bpf/bpf_helpers.h>
22 
23 static const int cfg_port = 8000;
24 
25 static const int cfg_udp_src = 20000;
26 
27 #define	L2_PAD_SZ	(sizeof(struct vxlanhdr) + ETH_HLEN)
28 
29 #define	UDP_PORT		5555
30 #define	MPLS_OVER_UDP_PORT	6635
31 #define	ETH_OVER_UDP_PORT	7777
32 #define	VXLAN_UDP_PORT		8472
33 
34 #define	EXTPROTO_VXLAN	0x1
35 
36 #define	VXLAN_N_VID     (1u << 24)
37 #define	VXLAN_VNI_MASK	bpf_htonl((VXLAN_N_VID - 1) << 8)
38 #define	VXLAN_FLAGS     0x8
39 #define	VXLAN_VNI       1
40 
41 /* MPLS label 1000 with S bit (last label) set and ttl of 255. */
42 static const __u32 mpls_label = __bpf_constant_htonl(1000 << 12 |
43 						     MPLS_LS_S_MASK | 0xff);
44 
45 struct vxlanhdr {
46 	__be32 vx_flags;
47 	__be32 vx_vni;
48 } __attribute__((packed));
49 
50 struct gre_hdr {
51 	__be16 flags;
52 	__be16 protocol;
53 } __attribute__((packed));
54 
55 union l4hdr {
56 	struct udphdr udp;
57 	struct gre_hdr gre;
58 };
59 
60 struct v4hdr {
61 	struct iphdr ip;
62 	union l4hdr l4hdr;
63 	__u8 pad[L2_PAD_SZ];		/* space for L2 header / vxlan header ... */
64 } __attribute__((packed));
65 
66 struct v6hdr {
67 	struct ipv6hdr ip;
68 	union l4hdr l4hdr;
69 	__u8 pad[L2_PAD_SZ];		/* space for L2 header / vxlan header ... */
70 } __attribute__((packed));
71 
72 static __always_inline void set_ipv4_csum(struct iphdr *iph)
73 {
74 	__u16 *iph16 = (__u16 *)iph;
75 	__u32 csum;
76 	int i;
77 
78 	iph->check = 0;
79 
80 #pragma clang loop unroll(full)
81 	for (i = 0, csum = 0; i < sizeof(*iph) >> 1; i++)
82 		csum += *iph16++;
83 
84 	iph->check = ~((csum & 0xffff) + (csum >> 16));
85 }
86 
87 static __always_inline int __encap_ipv4(struct __sk_buff *skb, __u8 encap_proto,
88 					__u16 l2_proto, __u16 ext_proto)
89 {
90 	__u16 udp_dst = UDP_PORT;
91 	struct iphdr iph_inner;
92 	struct v4hdr h_outer;
93 	struct tcphdr tcph;
94 	int olen, l2_len;
95 	__u8 *l2_hdr = NULL;
96 	int tcp_off;
97 	__u64 flags;
98 
99 	/* Most tests encapsulate a packet into a tunnel with the same
100 	 * network protocol, and derive the outer header fields from
101 	 * the inner header.
102 	 *
103 	 * The 6in4 case tests different inner and outer protocols. As
104 	 * the inner is ipv6, but the outer expects an ipv4 header as
105 	 * input, manually build a struct iphdr based on the ipv6hdr.
106 	 */
107 	if (encap_proto == IPPROTO_IPV6) {
108 		const __u32 saddr = (192 << 24) | (168 << 16) | (1 << 8) | 1;
109 		const __u32 daddr = (192 << 24) | (168 << 16) | (1 << 8) | 2;
110 		struct ipv6hdr iph6_inner;
111 
112 		/* Read the IPv6 header */
113 		if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph6_inner,
114 				       sizeof(iph6_inner)) < 0)
115 			return TC_ACT_OK;
116 
117 		/* Derive the IPv4 header fields from the IPv6 header */
118 		memset(&iph_inner, 0, sizeof(iph_inner));
119 		iph_inner.version = 4;
120 		iph_inner.ihl = 5;
121 		iph_inner.tot_len = bpf_htons(sizeof(iph6_inner) +
122 				    bpf_ntohs(iph6_inner.payload_len));
123 		iph_inner.ttl = iph6_inner.hop_limit - 1;
124 		iph_inner.protocol = iph6_inner.nexthdr;
125 		iph_inner.saddr = __bpf_constant_htonl(saddr);
126 		iph_inner.daddr = __bpf_constant_htonl(daddr);
127 
128 		tcp_off = sizeof(iph6_inner);
129 	} else {
130 		if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
131 				       sizeof(iph_inner)) < 0)
132 			return TC_ACT_OK;
133 
134 		tcp_off = sizeof(iph_inner);
135 	}
136 
137 	/* filter only packets we want */
138 	if (iph_inner.ihl != 5 || iph_inner.protocol != IPPROTO_TCP)
139 		return TC_ACT_OK;
140 
141 	if (bpf_skb_load_bytes(skb, ETH_HLEN + tcp_off,
142 			       &tcph, sizeof(tcph)) < 0)
143 		return TC_ACT_OK;
144 
145 	if (tcph.dest != __bpf_constant_htons(cfg_port))
146 		return TC_ACT_OK;
147 
148 	olen = sizeof(h_outer.ip);
149 	l2_len = 0;
150 
151 	flags = BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV4;
152 
153 	switch (l2_proto) {
154 	case ETH_P_MPLS_UC:
155 		l2_len = sizeof(mpls_label);
156 		udp_dst = MPLS_OVER_UDP_PORT;
157 		break;
158 	case ETH_P_TEB:
159 		l2_len = ETH_HLEN;
160 		if (ext_proto & EXTPROTO_VXLAN) {
161 			udp_dst = VXLAN_UDP_PORT;
162 			l2_len += sizeof(struct vxlanhdr);
163 		} else
164 			udp_dst = ETH_OVER_UDP_PORT;
165 		break;
166 	}
167 	flags |= BPF_F_ADJ_ROOM_ENCAP_L2(l2_len);
168 
169 	switch (encap_proto) {
170 	case IPPROTO_GRE:
171 		flags |= BPF_F_ADJ_ROOM_ENCAP_L4_GRE;
172 		olen += sizeof(h_outer.l4hdr.gre);
173 		h_outer.l4hdr.gre.protocol = bpf_htons(l2_proto);
174 		h_outer.l4hdr.gre.flags = 0;
175 		break;
176 	case IPPROTO_UDP:
177 		flags |= BPF_F_ADJ_ROOM_ENCAP_L4_UDP;
178 		olen += sizeof(h_outer.l4hdr.udp);
179 		h_outer.l4hdr.udp.source = __bpf_constant_htons(cfg_udp_src);
180 		h_outer.l4hdr.udp.dest = bpf_htons(udp_dst);
181 		h_outer.l4hdr.udp.check = 0;
182 		h_outer.l4hdr.udp.len = bpf_htons(bpf_ntohs(iph_inner.tot_len) +
183 						  sizeof(h_outer.l4hdr.udp) +
184 						  l2_len);
185 		break;
186 	case IPPROTO_IPIP:
187 	case IPPROTO_IPV6:
188 		break;
189 	default:
190 		return TC_ACT_OK;
191 	}
192 
193 	/* add L2 encap (if specified) */
194 	l2_hdr = (__u8 *)&h_outer + olen;
195 	switch (l2_proto) {
196 	case ETH_P_MPLS_UC:
197 		*(__u32 *)l2_hdr = mpls_label;
198 		break;
199 	case ETH_P_TEB:
200 		flags |= BPF_F_ADJ_ROOM_ENCAP_L2_ETH;
201 
202 		if (ext_proto & EXTPROTO_VXLAN) {
203 			struct vxlanhdr *vxlan_hdr = (struct vxlanhdr *)l2_hdr;
204 
205 			vxlan_hdr->vx_flags = VXLAN_FLAGS;
206 			vxlan_hdr->vx_vni = bpf_htonl((VXLAN_VNI & VXLAN_VNI_MASK) << 8);
207 
208 			l2_hdr += sizeof(struct vxlanhdr);
209 		}
210 
211 		if (bpf_skb_load_bytes(skb, 0, l2_hdr, ETH_HLEN))
212 			return TC_ACT_SHOT;
213 
214 		break;
215 	}
216 	olen += l2_len;
217 
218 	/* add room between mac and network header */
219 	if (bpf_skb_adjust_room(skb, olen, BPF_ADJ_ROOM_MAC, flags))
220 		return TC_ACT_SHOT;
221 
222 	/* prepare new outer network header */
223 	h_outer.ip = iph_inner;
224 	h_outer.ip.tot_len = bpf_htons(olen +
225 				       bpf_ntohs(h_outer.ip.tot_len));
226 	h_outer.ip.protocol = encap_proto;
227 
228 	set_ipv4_csum((void *)&h_outer.ip);
229 
230 	/* store new outer network header */
231 	if (bpf_skb_store_bytes(skb, ETH_HLEN, &h_outer, olen,
232 				BPF_F_INVALIDATE_HASH) < 0)
233 		return TC_ACT_SHOT;
234 
235 	/* if changing outer proto type, update eth->h_proto */
236 	if (encap_proto == IPPROTO_IPV6) {
237 		struct ethhdr eth;
238 
239 		if (bpf_skb_load_bytes(skb, 0, &eth, sizeof(eth)) < 0)
240 			return TC_ACT_SHOT;
241 		eth.h_proto = bpf_htons(ETH_P_IP);
242 		if (bpf_skb_store_bytes(skb, 0, &eth, sizeof(eth), 0) < 0)
243 			return TC_ACT_SHOT;
244 	}
245 
246 	return TC_ACT_OK;
247 }
248 
249 static __always_inline int encap_ipv4(struct __sk_buff *skb, __u8 encap_proto,
250 				      __u16 l2_proto)
251 {
252 	return __encap_ipv4(skb, encap_proto, l2_proto, 0);
253 }
254 
255 static __always_inline int __encap_ipv6(struct __sk_buff *skb, __u8 encap_proto,
256 					__u16 l2_proto, __u16 ext_proto)
257 {
258 	__u16 udp_dst = UDP_PORT;
259 	struct ipv6hdr iph_inner;
260 	struct v6hdr h_outer;
261 	struct tcphdr tcph;
262 	int olen, l2_len;
263 	__u8 *l2_hdr = NULL;
264 	__u16 tot_len;
265 	__u64 flags;
266 
267 	if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_inner,
268 			       sizeof(iph_inner)) < 0)
269 		return TC_ACT_OK;
270 
271 	/* filter only packets we want */
272 	if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph_inner),
273 			       &tcph, sizeof(tcph)) < 0)
274 		return TC_ACT_OK;
275 
276 	if (tcph.dest != __bpf_constant_htons(cfg_port))
277 		return TC_ACT_OK;
278 
279 	olen = sizeof(h_outer.ip);
280 	l2_len = 0;
281 
282 	flags = BPF_F_ADJ_ROOM_FIXED_GSO | BPF_F_ADJ_ROOM_ENCAP_L3_IPV6;
283 
284 	switch (l2_proto) {
285 	case ETH_P_MPLS_UC:
286 		l2_len = sizeof(mpls_label);
287 		udp_dst = MPLS_OVER_UDP_PORT;
288 		break;
289 	case ETH_P_TEB:
290 		l2_len = ETH_HLEN;
291 		if (ext_proto & EXTPROTO_VXLAN) {
292 			udp_dst = VXLAN_UDP_PORT;
293 			l2_len += sizeof(struct vxlanhdr);
294 		} else
295 			udp_dst = ETH_OVER_UDP_PORT;
296 		break;
297 	}
298 	flags |= BPF_F_ADJ_ROOM_ENCAP_L2(l2_len);
299 
300 	switch (encap_proto) {
301 	case IPPROTO_GRE:
302 		flags |= BPF_F_ADJ_ROOM_ENCAP_L4_GRE;
303 		olen += sizeof(h_outer.l4hdr.gre);
304 		h_outer.l4hdr.gre.protocol = bpf_htons(l2_proto);
305 		h_outer.l4hdr.gre.flags = 0;
306 		break;
307 	case IPPROTO_UDP:
308 		flags |= BPF_F_ADJ_ROOM_ENCAP_L4_UDP;
309 		olen += sizeof(h_outer.l4hdr.udp);
310 		h_outer.l4hdr.udp.source = __bpf_constant_htons(cfg_udp_src);
311 		h_outer.l4hdr.udp.dest = bpf_htons(udp_dst);
312 		tot_len = bpf_ntohs(iph_inner.payload_len) + sizeof(iph_inner) +
313 			  sizeof(h_outer.l4hdr.udp) + l2_len;
314 		h_outer.l4hdr.udp.check = 0;
315 		h_outer.l4hdr.udp.len = bpf_htons(tot_len);
316 		break;
317 	case IPPROTO_IPV6:
318 		break;
319 	default:
320 		return TC_ACT_OK;
321 	}
322 
323 	/* add L2 encap (if specified) */
324 	l2_hdr = (__u8 *)&h_outer + olen;
325 	switch (l2_proto) {
326 	case ETH_P_MPLS_UC:
327 		*(__u32 *)l2_hdr = mpls_label;
328 		break;
329 	case ETH_P_TEB:
330 		flags |= BPF_F_ADJ_ROOM_ENCAP_L2_ETH;
331 
332 		if (ext_proto & EXTPROTO_VXLAN) {
333 			struct vxlanhdr *vxlan_hdr = (struct vxlanhdr *)l2_hdr;
334 
335 			vxlan_hdr->vx_flags = VXLAN_FLAGS;
336 			vxlan_hdr->vx_vni = bpf_htonl((VXLAN_VNI & VXLAN_VNI_MASK) << 8);
337 
338 			l2_hdr += sizeof(struct vxlanhdr);
339 		}
340 
341 		if (bpf_skb_load_bytes(skb, 0, l2_hdr, ETH_HLEN))
342 			return TC_ACT_SHOT;
343 		break;
344 	}
345 	olen += l2_len;
346 
347 	/* add room between mac and network header */
348 	if (bpf_skb_adjust_room(skb, olen, BPF_ADJ_ROOM_MAC, flags))
349 		return TC_ACT_SHOT;
350 
351 	/* prepare new outer network header */
352 	h_outer.ip = iph_inner;
353 	h_outer.ip.payload_len = bpf_htons(olen +
354 					   bpf_ntohs(h_outer.ip.payload_len));
355 
356 	h_outer.ip.nexthdr = encap_proto;
357 
358 	/* store new outer network header */
359 	if (bpf_skb_store_bytes(skb, ETH_HLEN, &h_outer, olen,
360 				BPF_F_INVALIDATE_HASH) < 0)
361 		return TC_ACT_SHOT;
362 
363 	return TC_ACT_OK;
364 }
365 
366 static __always_inline int encap_ipv6(struct __sk_buff *skb, __u8 encap_proto,
367 				      __u16 l2_proto)
368 {
369 	return __encap_ipv6(skb, encap_proto, l2_proto, 0);
370 }
371 
372 SEC("encap_ipip_none")
373 int __encap_ipip_none(struct __sk_buff *skb)
374 {
375 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
376 		return encap_ipv4(skb, IPPROTO_IPIP, ETH_P_IP);
377 	else
378 		return TC_ACT_OK;
379 }
380 
381 SEC("encap_gre_none")
382 int __encap_gre_none(struct __sk_buff *skb)
383 {
384 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
385 		return encap_ipv4(skb, IPPROTO_GRE, ETH_P_IP);
386 	else
387 		return TC_ACT_OK;
388 }
389 
390 SEC("encap_gre_mpls")
391 int __encap_gre_mpls(struct __sk_buff *skb)
392 {
393 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
394 		return encap_ipv4(skb, IPPROTO_GRE, ETH_P_MPLS_UC);
395 	else
396 		return TC_ACT_OK;
397 }
398 
399 SEC("encap_gre_eth")
400 int __encap_gre_eth(struct __sk_buff *skb)
401 {
402 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
403 		return encap_ipv4(skb, IPPROTO_GRE, ETH_P_TEB);
404 	else
405 		return TC_ACT_OK;
406 }
407 
408 SEC("encap_udp_none")
409 int __encap_udp_none(struct __sk_buff *skb)
410 {
411 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
412 		return encap_ipv4(skb, IPPROTO_UDP, ETH_P_IP);
413 	else
414 		return TC_ACT_OK;
415 }
416 
417 SEC("encap_udp_mpls")
418 int __encap_udp_mpls(struct __sk_buff *skb)
419 {
420 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
421 		return encap_ipv4(skb, IPPROTO_UDP, ETH_P_MPLS_UC);
422 	else
423 		return TC_ACT_OK;
424 }
425 
426 SEC("encap_udp_eth")
427 int __encap_udp_eth(struct __sk_buff *skb)
428 {
429 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
430 		return encap_ipv4(skb, IPPROTO_UDP, ETH_P_TEB);
431 	else
432 		return TC_ACT_OK;
433 }
434 
435 SEC("encap_vxlan_eth")
436 int __encap_vxlan_eth(struct __sk_buff *skb)
437 {
438 	if (skb->protocol == __bpf_constant_htons(ETH_P_IP))
439 		return __encap_ipv4(skb, IPPROTO_UDP,
440 				    ETH_P_TEB,
441 				    EXTPROTO_VXLAN);
442 	else
443 		return TC_ACT_OK;
444 }
445 
446 SEC("encap_sit_none")
447 int __encap_sit_none(struct __sk_buff *skb)
448 {
449 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
450 		return encap_ipv4(skb, IPPROTO_IPV6, ETH_P_IP);
451 	else
452 		return TC_ACT_OK;
453 }
454 
455 SEC("encap_ip6tnl_none")
456 int __encap_ip6tnl_none(struct __sk_buff *skb)
457 {
458 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
459 		return encap_ipv6(skb, IPPROTO_IPV6, ETH_P_IPV6);
460 	else
461 		return TC_ACT_OK;
462 }
463 
464 SEC("encap_ip6gre_none")
465 int __encap_ip6gre_none(struct __sk_buff *skb)
466 {
467 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
468 		return encap_ipv6(skb, IPPROTO_GRE, ETH_P_IPV6);
469 	else
470 		return TC_ACT_OK;
471 }
472 
473 SEC("encap_ip6gre_mpls")
474 int __encap_ip6gre_mpls(struct __sk_buff *skb)
475 {
476 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
477 		return encap_ipv6(skb, IPPROTO_GRE, ETH_P_MPLS_UC);
478 	else
479 		return TC_ACT_OK;
480 }
481 
482 SEC("encap_ip6gre_eth")
483 int __encap_ip6gre_eth(struct __sk_buff *skb)
484 {
485 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
486 		return encap_ipv6(skb, IPPROTO_GRE, ETH_P_TEB);
487 	else
488 		return TC_ACT_OK;
489 }
490 
491 SEC("encap_ip6udp_none")
492 int __encap_ip6udp_none(struct __sk_buff *skb)
493 {
494 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
495 		return encap_ipv6(skb, IPPROTO_UDP, ETH_P_IPV6);
496 	else
497 		return TC_ACT_OK;
498 }
499 
500 SEC("encap_ip6udp_mpls")
501 int __encap_ip6udp_mpls(struct __sk_buff *skb)
502 {
503 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
504 		return encap_ipv6(skb, IPPROTO_UDP, ETH_P_MPLS_UC);
505 	else
506 		return TC_ACT_OK;
507 }
508 
509 SEC("encap_ip6udp_eth")
510 int __encap_ip6udp_eth(struct __sk_buff *skb)
511 {
512 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
513 		return encap_ipv6(skb, IPPROTO_UDP, ETH_P_TEB);
514 	else
515 		return TC_ACT_OK;
516 }
517 
518 SEC("encap_ip6vxlan_eth")
519 int __encap_ip6vxlan_eth(struct __sk_buff *skb)
520 {
521 	if (skb->protocol == __bpf_constant_htons(ETH_P_IPV6))
522 		return __encap_ipv6(skb, IPPROTO_UDP,
523 				    ETH_P_TEB,
524 				    EXTPROTO_VXLAN);
525 	else
526 		return TC_ACT_OK;
527 }
528 
529 static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
530 {
531 	char buf[sizeof(struct v6hdr)];
532 	struct gre_hdr greh;
533 	struct udphdr udph;
534 	int olen = len;
535 
536 	switch (proto) {
537 	case IPPROTO_IPIP:
538 	case IPPROTO_IPV6:
539 		break;
540 	case IPPROTO_GRE:
541 		olen += sizeof(struct gre_hdr);
542 		if (bpf_skb_load_bytes(skb, off + len, &greh, sizeof(greh)) < 0)
543 			return TC_ACT_OK;
544 		switch (bpf_ntohs(greh.protocol)) {
545 		case ETH_P_MPLS_UC:
546 			olen += sizeof(mpls_label);
547 			break;
548 		case ETH_P_TEB:
549 			olen += ETH_HLEN;
550 			break;
551 		}
552 		break;
553 	case IPPROTO_UDP:
554 		olen += sizeof(struct udphdr);
555 		if (bpf_skb_load_bytes(skb, off + len, &udph, sizeof(udph)) < 0)
556 			return TC_ACT_OK;
557 		switch (bpf_ntohs(udph.dest)) {
558 		case MPLS_OVER_UDP_PORT:
559 			olen += sizeof(mpls_label);
560 			break;
561 		case ETH_OVER_UDP_PORT:
562 			olen += ETH_HLEN;
563 			break;
564 		case VXLAN_UDP_PORT:
565 			olen += ETH_HLEN + sizeof(struct vxlanhdr);
566 			break;
567 		}
568 		break;
569 	default:
570 		return TC_ACT_OK;
571 	}
572 
573 	if (bpf_skb_adjust_room(skb, -olen, BPF_ADJ_ROOM_MAC,
574 				BPF_F_ADJ_ROOM_FIXED_GSO))
575 		return TC_ACT_SHOT;
576 
577 	return TC_ACT_OK;
578 }
579 
580 static int decap_ipv4(struct __sk_buff *skb)
581 {
582 	struct iphdr iph_outer;
583 
584 	if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_outer,
585 			       sizeof(iph_outer)) < 0)
586 		return TC_ACT_OK;
587 
588 	if (iph_outer.ihl != 5)
589 		return TC_ACT_OK;
590 
591 	return decap_internal(skb, ETH_HLEN, sizeof(iph_outer),
592 			      iph_outer.protocol);
593 }
594 
595 static int decap_ipv6(struct __sk_buff *skb)
596 {
597 	struct ipv6hdr iph_outer;
598 
599 	if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph_outer,
600 			       sizeof(iph_outer)) < 0)
601 		return TC_ACT_OK;
602 
603 	return decap_internal(skb, ETH_HLEN, sizeof(iph_outer),
604 			      iph_outer.nexthdr);
605 }
606 
607 SEC("decap")
608 int decap_f(struct __sk_buff *skb)
609 {
610 	switch (skb->protocol) {
611 	case __bpf_constant_htons(ETH_P_IP):
612 		return decap_ipv4(skb);
613 	case __bpf_constant_htons(ETH_P_IPV6):
614 		return decap_ipv6(skb);
615 	default:
616 		/* does not match, ignore */
617 		return TC_ACT_OK;
618 	}
619 }
620 
621 char __license[] SEC("license") = "GPL";
622