1// SPDX-License-Identifier: GPL-2.0
2#include <stddef.h>
3#include <string.h>
4#include <linux/bpf.h>
5#include <linux/ip.h>
6#include <linux/ipv6.h>
7#include <bpf/bpf_helpers.h>
8#include <bpf/bpf_endian.h>
9
10struct grehdr {
11	__be16 flags;
12	__be16 protocol;
13};
14
15SEC("encap_gre")
16int bpf_lwt_encap_gre(struct __sk_buff *skb)
17{
18	struct encap_hdr {
19		struct iphdr iph;
20		struct grehdr greh;
21	} hdr;
22	int err;
23
24	memset(&hdr, 0, sizeof(struct encap_hdr));
25
26	hdr.iph.ihl = 5;
27	hdr.iph.version = 4;
28	hdr.iph.ttl = 0x40;
29	hdr.iph.protocol = 47;  /* IPPROTO_GRE */
30#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
31	hdr.iph.saddr = 0x640110ac;  /* 172.16.1.100 */
32	hdr.iph.daddr = 0x641010ac;  /* 172.16.16.100 */
33#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
34	hdr.iph.saddr = 0xac100164;  /* 172.16.1.100 */
35	hdr.iph.daddr = 0xac101064;  /* 172.16.16.100 */
36#else
37#error "Fix your compiler's __BYTE_ORDER__?!"
38#endif
39	hdr.iph.tot_len = bpf_htons(skb->len + sizeof(struct encap_hdr));
40
41	hdr.greh.protocol = skb->protocol;
42
43	err = bpf_lwt_push_encap(skb, BPF_LWT_ENCAP_IP, &hdr,
44				 sizeof(struct encap_hdr));
45	if (err)
46		return BPF_DROP;
47
48	return BPF_LWT_REROUTE;
49}
50
51SEC("encap_gre6")
52int bpf_lwt_encap_gre6(struct __sk_buff *skb)
53{
54	struct encap_hdr {
55		struct ipv6hdr ip6hdr;
56		struct grehdr greh;
57	} hdr;
58	int err;
59
60	memset(&hdr, 0, sizeof(struct encap_hdr));
61
62	hdr.ip6hdr.version = 6;
63	hdr.ip6hdr.payload_len = bpf_htons(skb->len + sizeof(struct grehdr));
64	hdr.ip6hdr.nexthdr = 47;  /* IPPROTO_GRE */
65	hdr.ip6hdr.hop_limit = 0x40;
66	/* fb01::1 */
67	hdr.ip6hdr.saddr.s6_addr[0] = 0xfb;
68	hdr.ip6hdr.saddr.s6_addr[1] = 1;
69	hdr.ip6hdr.saddr.s6_addr[15] = 1;
70	/* fb10::1 */
71	hdr.ip6hdr.daddr.s6_addr[0] = 0xfb;
72	hdr.ip6hdr.daddr.s6_addr[1] = 0x10;
73	hdr.ip6hdr.daddr.s6_addr[15] = 1;
74
75	hdr.greh.protocol = skb->protocol;
76
77	err = bpf_lwt_push_encap(skb, BPF_LWT_ENCAP_IP, &hdr,
78				 sizeof(struct encap_hdr));
79	if (err)
80		return BPF_DROP;
81
82	return BPF_LWT_REROUTE;
83}
84
85char _license[] SEC("license") = "GPL";
86