c - linux-kernel 模块中的系统调用拦截(内核 3.5)

Question

我需要用我自己的实现替换标准系统调用(例如 SYS_mkdir)。

正如我在一些资源中读到的，包括 this question在 Stackoverflow 上，sys_call_table 自内核版本 2.6 以来未导出符号。

我尝试了以下代码:

    #include <linux/module.h> 
    #include <linux/kernel.h> 
    #include <linux/unistd.h> 
    #include <asm/syscall.h> 

    int (*orig_mkdir)(const char *path); 

    ....

    int init_module(void) 
    { 
            orig_mkdir=sys_call_table[__NR_mkdir]; 
            sys_call_table[__NR_mkdir]=own_mkdir;  
            printk("sys_mkdir replaced\n"); 
            return(0); 
    } 

    ....

不幸的是我收到编译器错误:

 error: assignment of read-only location ‘sys_call_table[83]’

如何替换系统调用？

编辑:有没有不打内核补丁的解决方案？

Answer 1

这对我有用。

见 Linux Kernel: System call hooking example和 https://bbs.archlinux.org/viewtopic.php?id=139406

asmlinkage long (*ref_sys_open)(const char __user *filename, int flags, umode_t mode);
asmlinkage long new_sys_open(const char __user *filename, int flags, umode_t mode)
{
  return ref_sys_open(filename, flags, mode);
}

static unsigned long **aquire_sys_call_table(void)
{
  unsigned long int offset = PAGE_OFFSET;
  unsigned long **sct;

  while (offset < ULLONG_MAX) {
    sct = (unsigned long **)offset;

    if (sct[__NR_close] == (unsigned long *) sys_close) 
      return sct;

    offset += sizeof(void *);
  }
  print("Getting syscall table failed. :(");
  return NULL;
}


// Crazy copypasted asm stuff. Could use linux function as well...
// but this works and will work in the future they say.
static void disable_page_protection(void) 
{
  unsigned long value;
  asm volatile("mov %%cr0, %0" : "=r" (value));

  if(!(value & 0x00010000))
    return;

  asm volatile("mov %0, %%cr0" : : "r" (value & ~0x00010000));
}

static void enable_page_protection(void) 
{
  unsigned long value;
  asm volatile("mov %%cr0, %0" : "=r" (value));

  if((value & 0x00010000))
    return;

  asm volatile("mov %0, %%cr0" : : "r" (value | 0x00010000));
}


static int __init rootkit_start(void) 
{

  //Hide me

  print("loaded");

  if(!(sys_call_table = aquire_sys_call_table()))
    return -1;

  disable_page_protection(); 
  {
    ref_sys_open = (void *)sys_call_table[__NR_open];
    sys_call_table[__NR_open] = (unsigned long *)new_sys_open;
  }
  enable_page_protection();
  return 0;
}

static void __exit rootkit_end(void) 
{
  print("exiting");

  if(!sys_call_table) {
    return;
  }

  disable_page_protection();
  {
    sys_call_table[__NR_open] = (unsigned long *)ref_sys_open;
  }
  enable_page_protection();
}