1 /* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me> 2 * 3 * This program is free software; you can redistribute it and/or 4 * modify it under the terms of version 2 of the GNU General Public 5 * License as published by the Free Software Foundation. 6 */ 7 #include "vmlinux.h" 8 #include <string.h> 9 #include <linux/version.h> 10 #include <bpf/bpf_helpers.h> 11 #include <bpf/bpf_tracing.h> 12 #include <bpf/bpf_core_read.h> 13 14 struct { 15 __uint(type, BPF_MAP_TYPE_HASH); 16 __type(key, struct sockaddr_in); 17 __type(value, struct sockaddr_in); 18 __uint(max_entries, 256); 19 } dnat_map SEC(".maps"); 20 21 /* kprobe is NOT a stable ABI 22 * kernel functions can be removed, renamed or completely change semantics. 23 * Number of arguments and their positions can change, etc. 24 * In such case this bpf+kprobe example will no longer be meaningful 25 * 26 * This example sits on a syscall, and the syscall ABI is relatively stable 27 * of course, across platforms, and over time, the ABI may change. 28 */ 29 SEC("ksyscall/connect") 30 int bpf_prog1(struct pt_regs *ctx) 31 { 32 struct pt_regs *real_regs = (struct pt_regs *)PT_REGS_PARM1_CORE(ctx); 33 void *sockaddr_arg = (void *)PT_REGS_PARM2_CORE(real_regs); 34 int sockaddr_len = (int)PT_REGS_PARM3_CORE(real_regs); 35 struct sockaddr_in new_addr, orig_addr = {}; 36 struct sockaddr_in *mapped_addr; 37 38 if (sockaddr_len > sizeof(orig_addr)) 39 return 0; 40 41 if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0) 42 return 0; 43 44 mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr); 45 if (mapped_addr != NULL) { 46 memcpy(&new_addr, mapped_addr, sizeof(new_addr)); 47 bpf_probe_write_user(sockaddr_arg, &new_addr, 48 sizeof(new_addr)); 49 } 50 return 0; 51 } 52 53 char _license[] SEC("license") = "GPL"; 54 u32 _version SEC("version") = LINUX_VERSION_CODE; 55