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 #define SRC1_IP4 0xAC100001U /* 172.16.0.1 */ 12 #define SRC2_IP4 0x00000000U 13 #define SRC_REWRITE_IP4 0x7f000004U 14 #define DST_IP4 0xC0A801FEU /* 192.168.1.254 */ 15 #define DST_REWRITE_IP4 0x7f000001U 16 #define DST_PORT 4040 17 #define DST_REWRITE_PORT4 4444 18 19 int _version SEC("version") = 1; 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 /* Rewrite source. */ 28 if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) || 29 ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) { 30 ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4); 31 } else { 32 /* Unexpected source. Reject sendmsg. */ 33 return 0; 34 } 35 36 /* Rewrite destination. */ 37 if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) && 38 ctx->user_port == bpf_htons(DST_PORT)) { 39 ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4); 40 ctx->user_port = bpf_htons(DST_REWRITE_PORT4); 41 } else { 42 /* Unexpected source. Reject sendmsg. */ 43 return 0; 44 } 45 46 return 1; 47 } 48 49 char _license[] SEC("license") = "GPL"; 50