// SPDX-License-Identifier: GPL-2.0 // Copyright (c) 2018 Facebook #include <linux/stddef.h> #include <linux/bpf.h> #include <sys/socket.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> #include <bpf_sockopt_helpers.h> #define SRC1_IP4 0xAC100001U /* 172.16.0.1 */ #define SRC2_IP4 0x00000000U #define SRC_REWRITE_IP4 0x7f000004U #define DST_IP4 0xC0A801FEU /* 192.168.1.254 */ #define DST_REWRITE_IP4 0x7f000001U #define DST_PORT 4040 #define DST_REWRITE_PORT4 4444 SEC("cgroup/sendmsg4") int sendmsg_v4_prog(struct bpf_sock_addr *ctx) { int prio; if (ctx->type != SOCK_DGRAM) return 0; if (!get_set_sk_priority(ctx)) return 0; /* Rewrite source. */ if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) || ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) { ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4); } else { /* Unexpected source. Reject sendmsg. */ return 0; } /* Rewrite destination. */ if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) && ctx->user_port == bpf_htons(DST_PORT)) { ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4); ctx->user_port = bpf_htons(DST_REWRITE_PORT4); } else { /* Unexpected source. Reject sendmsg. */ return 0; } return 1; } char _license[] SEC("license") = "GPL";