1
2#include <stdint.h>
3#include <stdbool.h>
4#include <stddef.h>
5
6#include <linux/bpf.h>
7#include <linux/stddef.h>
8#include <linux/pkt_cls.h>
9#include <linux/if_ether.h>
10#include <linux/in.h>
11#include <linux/ip.h>
12#include <linux/ipv6.h>
13
14#include <bpf/bpf_helpers.h>
15#include <bpf/bpf_endian.h>
16
17#ifndef ctx_ptr
18# define ctx_ptr(field) (void *)(long)(field)
19#endif
20
21#define AF_INET 2
22#define AF_INET6 10
23
24static __always_inline int fill_fib_params_v4(struct __sk_buff *skb,
25 struct bpf_fib_lookup *fib_params)
26{
27 void *data_end = ctx_ptr(skb->data_end);
28 void *data = ctx_ptr(skb->data);
29 struct iphdr *ip4h;
30
31 if (data + sizeof(struct ethhdr) > data_end)
32 return -1;
33
34 ip4h = (struct iphdr *)(data + sizeof(struct ethhdr));
35 if ((void *)(ip4h + 1) > data_end)
36 return -1;
37
38 fib_params->family = AF_INET;
39 fib_params->tos = ip4h->tos;
40 fib_params->l4_protocol = ip4h->protocol;
41 fib_params->sport = 0;
42 fib_params->dport = 0;
43 fib_params->tot_len = bpf_ntohs(ip4h->tot_len);
44 fib_params->ipv4_src = ip4h->saddr;
45 fib_params->ipv4_dst = ip4h->daddr;
46
47 return 0;
48}
49
50static __always_inline int fill_fib_params_v6(struct __sk_buff *skb,
51 struct bpf_fib_lookup *fib_params)
52{
53 struct in6_addr *src = (struct in6_addr *)fib_params->ipv6_src;
54 struct in6_addr *dst = (struct in6_addr *)fib_params->ipv6_dst;
55 void *data_end = ctx_ptr(skb->data_end);
56 void *data = ctx_ptr(skb->data);
57 struct ipv6hdr *ip6h;
58
59 if (data + sizeof(struct ethhdr) > data_end)
60 return -1;
61
62 ip6h = (struct ipv6hdr *)(data + sizeof(struct ethhdr));
63 if ((void *)(ip6h + 1) > data_end)
64 return -1;
65
66 fib_params->family = AF_INET6;
67 fib_params->flowinfo = 0;
68 fib_params->l4_protocol = ip6h->nexthdr;
69 fib_params->sport = 0;
70 fib_params->dport = 0;
71 fib_params->tot_len = bpf_ntohs(ip6h->payload_len);
72 *src = ip6h->saddr;
73 *dst = ip6h->daddr;
74
75 return 0;
76}
77
78SEC("tc")
79int tc_chk(struct __sk_buff *skb)
80{
81 void *data_end = ctx_ptr(skb->data_end);
82 void *data = ctx_ptr(skb->data);
83 __u32 *raw = data;
84
85 if (data + sizeof(struct ethhdr) > data_end)
86 return TC_ACT_SHOT;
87
88 return !raw[0] && !raw[1] && !raw[2] ? TC_ACT_SHOT : TC_ACT_OK;
89}
90
91static __always_inline int tc_redir(struct __sk_buff *skb)
92{
93 struct bpf_fib_lookup fib_params = { .ifindex = skb->ingress_ifindex };
94 __u8 zero[ETH_ALEN * 2];
95 int ret = -1;
96
97 switch (skb->protocol) {
98 case __bpf_constant_htons(ETH_P_IP):
99 ret = fill_fib_params_v4(skb, &fib_params);
100 break;
101 case __bpf_constant_htons(ETH_P_IPV6):
102 ret = fill_fib_params_v6(skb, &fib_params);
103 break;
104 }
105
106 if (ret)
107 return TC_ACT_OK;
108
109 ret = bpf_fib_lookup(skb, &fib_params, sizeof(fib_params), 0);
110 if (ret == BPF_FIB_LKUP_RET_NOT_FWDED || ret < 0)
111 return TC_ACT_OK;
112
113 __builtin_memset(&zero, 0, sizeof(zero));
114 if (bpf_skb_store_bytes(skb, 0, &zero, sizeof(zero), 0) < 0)
115 return TC_ACT_SHOT;
116
117 if (ret == BPF_FIB_LKUP_RET_NO_NEIGH) {
118 struct bpf_redir_neigh nh_params = {};
119
120 nh_params.nh_family = fib_params.family;
121 __builtin_memcpy(&nh_params.ipv6_nh, &fib_params.ipv6_dst,
122 sizeof(nh_params.ipv6_nh));
123
124 return bpf_redirect_neigh(fib_params.ifindex, &nh_params,
125 sizeof(nh_params), 0);
126
127 } else if (ret == BPF_FIB_LKUP_RET_SUCCESS) {
128 void *data_end = ctx_ptr(skb->data_end);
129 struct ethhdr *eth = ctx_ptr(skb->data);
130
131 if (eth + 1 > data_end)
132 return TC_ACT_SHOT;
133
134 __builtin_memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
135 __builtin_memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
136
137 return bpf_redirect(fib_params.ifindex, 0);
138 }
139
140 return TC_ACT_SHOT;
141}
142
143
144
145
146SEC("tc")
147int tc_dst(struct __sk_buff *skb)
148{
149 return tc_redir(skb);
150}
151
152SEC("tc")
153int tc_src(struct __sk_buff *skb)
154{
155 return tc_redir(skb);
156}
157
158char __license[] SEC("license") = "GPL";
159
