1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0 2*4882a593Smuzhiyun // Copyright (c) 2018 Facebook 3*4882a593Smuzhiyun 4*4882a593Smuzhiyun #include <linux/stddef.h> 5*4882a593Smuzhiyun #include <linux/bpf.h> 6*4882a593Smuzhiyun #include <sys/socket.h> 7*4882a593Smuzhiyun 8*4882a593Smuzhiyun #include <bpf/bpf_helpers.h> 9*4882a593Smuzhiyun #include <bpf/bpf_endian.h> 10*4882a593Smuzhiyun 11*4882a593Smuzhiyun #define SRC1_IP4 0xAC100001U /* 172.16.0.1 */ 12*4882a593Smuzhiyun #define SRC2_IP4 0x00000000U 13*4882a593Smuzhiyun #define SRC_REWRITE_IP4 0x7f000004U 14*4882a593Smuzhiyun #define DST_IP4 0xC0A801FEU /* 192.168.1.254 */ 15*4882a593Smuzhiyun #define DST_REWRITE_IP4 0x7f000001U 16*4882a593Smuzhiyun #define DST_PORT 4040 17*4882a593Smuzhiyun #define DST_REWRITE_PORT4 4444 18*4882a593Smuzhiyun 19*4882a593Smuzhiyun int _version SEC("version") = 1; 20*4882a593Smuzhiyun 21*4882a593Smuzhiyun SEC("cgroup/sendmsg4") sendmsg_v4_prog(struct bpf_sock_addr * ctx)22*4882a593Smuzhiyunint sendmsg_v4_prog(struct bpf_sock_addr *ctx) 23*4882a593Smuzhiyun { 24*4882a593Smuzhiyun if (ctx->type != SOCK_DGRAM) 25*4882a593Smuzhiyun return 0; 26*4882a593Smuzhiyun 27*4882a593Smuzhiyun /* Rewrite source. */ 28*4882a593Smuzhiyun if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) || 29*4882a593Smuzhiyun ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) { 30*4882a593Smuzhiyun ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4); 31*4882a593Smuzhiyun } else { 32*4882a593Smuzhiyun /* Unexpected source. Reject sendmsg. */ 33*4882a593Smuzhiyun return 0; 34*4882a593Smuzhiyun } 35*4882a593Smuzhiyun 36*4882a593Smuzhiyun /* Rewrite destination. */ 37*4882a593Smuzhiyun if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) && 38*4882a593Smuzhiyun ctx->user_port == bpf_htons(DST_PORT)) { 39*4882a593Smuzhiyun ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4); 40*4882a593Smuzhiyun ctx->user_port = bpf_htons(DST_REWRITE_PORT4); 41*4882a593Smuzhiyun } else { 42*4882a593Smuzhiyun /* Unexpected source. Reject sendmsg. */ 43*4882a593Smuzhiyun return 0; 44*4882a593Smuzhiyun } 45*4882a593Smuzhiyun 46*4882a593Smuzhiyun return 1; 47*4882a593Smuzhiyun } 48*4882a593Smuzhiyun 49*4882a593Smuzhiyun char _license[] SEC("license") = "GPL"; 50