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_helpers.h"
8 #include "bpf_endian.h"
9 
10 struct grehdr {
11 	__be16 flags;
12 	__be16 protocol;
13 };
14 
15 SEC("encap_gre")
16 int 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 
51 SEC("encap_gre6")
52 int 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 
85 char _license[] SEC("license") = "GPL";
86