| 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 | char _license[] SEC("license") = "GPL"; |
| 53 |