Linux下系统调用的hook机制

[http://blog.csdn.net/sdulibh/article/details/42078681]
http://0pointer.de/blog/projects/mutrace.html
http://0pointer.de/blog/projects/mutrace.html – 对mutex进行trace的hook
https://github.com/dbpercona/mutrace/blob/master/README

• linux下系统调用hook机制的原理
  
  • LD_PRELOAD机制：允许用户手动指定使用的动态链接库，将系统库函数hook->lib.so.6
  • dlyopen;dlsym: 通过句柄和连接符名称获取真实库函数名或者变量名
• 实例
  
  • main.c
  • 编译：gcc -o main main.c

#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
  if( strcmp(argv[1], "123") )
  {
    printf("Incorrect\n");
  }
  else
  {
    printf("Correct\n");
  }
  return 0;
}

• hook.c
• 编译：gcc -fPIC -shared -o hook.so hook.c -ldl

#include<stdio.h>
#include<string.h>
#include<dlfcn.h>
typedef int (*STRCMP) (const char*, const char*);
int strcmp(const char* s1, const char* s2) {
        static void *handle = NULL;
        static STRCMP old_strcmp = NULL;
        if(!handle) {
                handle = dlopen("libc.so.6", RTLD_LAZY);
                old_strcmp = (STRCMP)dlsym(handle, "strcmp");
        }
        if(old_strcmp) printf("addr=%p\n", old_strcmp);
        printf("you are hacked. s1=<%s>,s2=<%s>\n", s1, s2);
        return old_strcmp(s1, s2);
}

• 运行： LD_PRELOAD= ./hook.so ./main 123

未完待续…