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") sendmsg_v4_prog(struct bpf_sock_addr * ctx)22int 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") sendmsg_v4_deny_prog(struct bpf_sock_addr * ctx)53int sendmsg_v4_deny_prog(struct bpf_sock_addr *ctx) 54 { 55 return 0; 56 } 57 58 char _license[] SEC("license") = "GPL"; 59