1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/bpf.h>
3 #include <bpf/bpf_endian.h>
4 #include <bpf/bpf_helpers.h>
5 #include <linux/ip.h>
6 #include "bpf_tracing_net.h"
7
8 /* We don't care about whether the packet can be received by network stack.
9 * Just care if the packet is sent to the correct device at correct direction
10 * and not panic the kernel.
11 */
prepend_dummy_mac(struct __sk_buff * skb)12 static int prepend_dummy_mac(struct __sk_buff *skb)
13 {
14 char mac[] = {0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0xf,
15 0xe, 0xd, 0xc, 0xb, 0xa, 0x08, 0x00};
16
17 if (bpf_skb_change_head(skb, ETH_HLEN, 0))
18 return -1;
19
20 if (bpf_skb_store_bytes(skb, 0, mac, sizeof(mac), 0))
21 return -1;
22
23 return 0;
24 }
25
26 /* Use the last byte of IP address to redirect the packet */
get_redirect_target(struct __sk_buff * skb)27 static int get_redirect_target(struct __sk_buff *skb)
28 {
29 struct iphdr *iph = NULL;
30 void *start = (void *)(long)skb->data;
31 void *end = (void *)(long)skb->data_end;
32
33 if (start + sizeof(*iph) > end)
34 return -1;
35
36 iph = (struct iphdr *)start;
37 return bpf_ntohl(iph->daddr) & 0xff;
38 }
39
40 SEC("redir_ingress")
test_lwt_redirect_in(struct __sk_buff * skb)41 int test_lwt_redirect_in(struct __sk_buff *skb)
42 {
43 int target = get_redirect_target(skb);
44
45 if (target < 0)
46 return BPF_OK;
47
48 if (prepend_dummy_mac(skb))
49 return BPF_DROP;
50
51 return bpf_redirect(target, BPF_F_INGRESS);
52 }
53
54 SEC("redir_egress")
test_lwt_redirect_out(struct __sk_buff * skb)55 int test_lwt_redirect_out(struct __sk_buff *skb)
56 {
57 int target = get_redirect_target(skb);
58
59 if (target < 0)
60 return BPF_OK;
61
62 if (prepend_dummy_mac(skb))
63 return BPF_DROP;
64
65 return bpf_redirect(target, 0);
66 }
67
68 SEC("redir_egress_nomac")
test_lwt_redirect_out_nomac(struct __sk_buff * skb)69 int test_lwt_redirect_out_nomac(struct __sk_buff *skb)
70 {
71 int target = get_redirect_target(skb);
72
73 if (target < 0)
74 return BPF_OK;
75
76 return bpf_redirect(target, 0);
77 }
78
79 SEC("redir_ingress_nomac")
test_lwt_redirect_in_nomac(struct __sk_buff * skb)80 int test_lwt_redirect_in_nomac(struct __sk_buff *skb)
81 {
82 int target = get_redirect_target(skb);
83
84 if (target < 0)
85 return BPF_OK;
86
87 return bpf_redirect(target, BPF_F_INGRESS);
88 }
89
90 char _license[] SEC("license") = "GPL";
91