test_probe_write_user_kern.c 1.8 KB

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  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 <linux/skbuff.h>
  8. #include <linux/netdevice.h>
  9. #include <uapi/linux/bpf.h>
  10. #include <linux/version.h>
  11. #include <bpf/bpf_helpers.h>
  12. #include <bpf/bpf_tracing.h>
  13. #include <bpf/bpf_core_read.h>
  14. #include "trace_common.h"
  15. struct {
  16. __uint(type, BPF_MAP_TYPE_HASH);
  17. __type(key, struct sockaddr_in);
  18. __type(value, struct sockaddr_in);
  19. __uint(max_entries, 256);
  20. } dnat_map SEC(".maps");
  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("kprobe/" SYSCALL(sys_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. if (sockaddr_len > sizeof(orig_addr))
  38. return 0;
  39. if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0)
  40. return 0;
  41. mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
  42. if (mapped_addr != NULL) {
  43. memcpy(&new_addr, mapped_addr, sizeof(new_addr));
  44. bpf_probe_write_user(sockaddr_arg, &new_addr,
  45. sizeof(new_addr));
  46. }
  47. return 0;
  48. }
  49. char _license[] SEC("license") = "GPL";
  50. u32 _version SEC("version") = LINUX_VERSION_CODE;