1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2018 Facebook
3
4 #include <linux/stddef.h>
5 #include <linux/bpf.h>
6 #include <sys/socket.h>
7
8 #include <bpf/bpf_helpers.h>
9 #include <bpf/bpf_endian.h>
10
11 #include <bpf_sockopt_helpers.h>
12
13 #define SRC1_IP4 0xAC100001U /* 172.16.0.1 */
14 #define SRC2_IP4 0x00000000U
15 #define SRC_REWRITE_IP4 0x7f000004U
16 #define DST_IP4 0xC0A801FEU /* 192.168.1.254 */
17 #define DST_REWRITE_IP4 0x7f000001U
18 #define DST_PORT 4040
19 #define DST_REWRITE_PORT4 4444
20
21 SEC("cgroup/sendmsg4")
22 int sendmsg_v4_prog(struct bpf_sock_addr *ctx)
23 {
24 if (ctx->type != SOCK_DGRAM)
25 return 0;
26
27 if (!get_set_sk_priority(ctx))
28 return 0;
29
30 /* Rewrite source. */
31 if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
32 ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
33 ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
34 } else {
35 /* Unexpected source. Reject sendmsg. */
36 return 0;
37 }
38
39 /* Rewrite destination. */
40 if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
41 ctx->user_port == bpf_htons(DST_PORT)) {
42 ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
43 ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
44 } else {
45 /* Unexpected source. Reject sendmsg. */
46 return 0;
47 }
48
49 return 1;
50 }
51
52 SEC("cgroup/sendmsg4")
53 int sendmsg_v4_deny_prog(struct bpf_sock_addr *ctx)
54 {
55 return 0;
56 }
57
58 char _license[] SEC("license") = "GPL";
59
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