FSOP，glibc-2.23攻击IO_list_all

文章目录

FSOP

FSOP

介绍：

FSOP 是 File Stream Oriented Programming 的缩写，根据前面对 FILE 的介绍得知进程内所有的 _ IO_FILE 结构会使用 _ chain 域相互连接形成一个链表，这个链表的头部由_IO_list_all 维护。
FSOP 的核心思想就是劫持_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。

关键函数**_IO_flush_all_lockp**：

c 复制代码

int
_IO_flush_all_lockp (int do_lock)
{
  ...
  fp = (_IO_FILE *) _IO_list_all;
  while (fp != NULL)
  {
       ...
       if (((fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base))
               && _IO_OVERFLOW (fp, EOF) == EOF)
           {
               result = EOF;
          }
        ...
  }
}

FOSP链执行流程：

malloc中unsorted bin出错会调用malloc_printerr 输出错误：

malloc_printerr 函数：

跟进__libc_message函数，最后也调用了abort函数：

c 复制代码

/* Abort with an error message.  */
void
__libc_message (int do_abort, const char *fmt, ...)
{
  va_list ap;
  int fd = -1;

  va_start (ap, fmt);

#ifdef FATAL_PREPARE
  FATAL_PREPARE;
#endif

  /* Open a descriptor for /dev/tty unless the user explicitly
     requests errors on standard error.  */
  const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
  if (on_2 == NULL || *on_2 == '\0')
    fd = open_not_cancel_2 (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);

  if (fd == -1)
    fd = STDERR_FILENO;

  struct str_list *list = NULL;
  int nlist = 0;

  const char *cp = fmt;
  while (*cp != '\0')
    {
      /* Find the next "%s" or the end of the string.  */
      const char *next = cp;
      while (next[0] != '%' || next[1] != 's')
	{
	  next = __strchrnul (next + 1, '%');

	  if (next[0] == '\0')
	    break;
	}

      /* Determine what to print.  */
      const char *str;
      size_t len;
      if (cp[0] == '%' && cp[1] == 's')
	{
	  str = va_arg (ap, const char *);
	  len = strlen (str);
	  cp += 2;
	}
      else
	{
	  str = cp;
	  len = next - cp;
	  cp = next;
	}

      struct str_list *newp = alloca (sizeof (struct str_list));
      newp->str = str;
      newp->len = len;
      newp->next = list;
      list = newp;
      ++nlist;
    }

  bool written = false;
  if (nlist > 0)
    {
      struct iovec *iov = alloca (nlist * sizeof (struct iovec));
      ssize_t total = 0;

      for (int cnt = nlist - 1; cnt >= 0; --cnt)
	{
	  iov[cnt].iov_base = (char *) list->str;
	  iov[cnt].iov_len = list->len;
	  total += list->len;
	  list = list->next;
	}

      written = WRITEV_FOR_FATAL (fd, iov, nlist, total);

      if (do_abort)
	{
	  total = ((total + 1 + GLRO(dl_pagesize) - 1)
		   & ~(GLRO(dl_pagesize) - 1));
	  struct abort_msg_s *buf = __mmap (NULL, total,
					    PROT_READ | PROT_WRITE,
					    MAP_ANON | MAP_PRIVATE, -1, 0);
	  if (__glibc_likely (buf != MAP_FAILED))
	    {
	      buf->size = total;
	      char *wp = buf->msg;
	      for (int cnt = 0; cnt < nlist; ++cnt)
		wp = mempcpy (wp, iov[cnt].iov_base, iov[cnt].iov_len);
	      *wp = '\0';

	      /* We have to free the old buffer since the application might
		 catch the SIGABRT signal.  */
	      struct abort_msg_s *old = atomic_exchange_acq (&__abort_msg,
							     buf);
	      if (old != NULL)
		__munmap (old, old->size);
	    }
	}
    }
  va_end (ap);
  if (do_abort)
    {
      BEFORE_ABORT (do_abort, written, fd);

      /* Kill the application.  */
      abort ();
    }
}

跟进abort函数，其中调用了fflush函数：

c 复制代码

/* Cause an abnormal program termination with core-dump.  */
void
abort (void)
{
  struct sigaction act;
  sigset_t sigs;

  /* First acquire the lock.  */
  __libc_lock_lock_recursive (lock);

  /* Now it's for sure we are alone.  But recursive calls are possible.  */

  /* Unlock SIGABRT.  */
  if (stage == 0)
    {
      ++stage;
      if (__sigemptyset (&sigs) == 0 &&
	  __sigaddset (&sigs, SIGABRT) == 0)
	__sigprocmask (SIG_UNBLOCK, &sigs, (sigset_t *) NULL);
    }

  /* Flush all streams.  We cannot close them now because the user
     might have registered a handler for SIGABRT.  */
  if (stage == 1)
    {
      ++stage;
      fflush (NULL);
    }
······
}

跟进fflush函数，fflush是一个宏定义，调用了IO_fflush函数，且参数是NULL：

继续跟进IO_fflush(NULL)，由于传入的参数为NULL，所以会调用_IO_flush_all函数:

c 复制代码

int
_IO_fflush (_IO_FILE *fp)
{
  if (fp == NULL)
    return _IO_flush_all ();
  else
    {
      int result;
      CHECK_FILE (fp, EOF);
      _IO_acquire_lock (fp);
      result = _IO_SYNC (fp) ? EOF : 0;
      _IO_release_lock (fp);
      return result;
    }
}

跟进_IO_flush_all函数，_IO_flush_all_lockp调用了_IO_flush_all_lockp(1)：

c 复制代码

int
_IO_flush_all (void)
{
  /* We want locking.  */
  return _IO_flush_all_lockp (1);
}

跟进_IO_flush_all_lockp(1)，而 _IO_flush_all_lockp就是这条FILE终点:

c 复制代码

int
_IO_flush_all_lockp (int do_lock)
{
  int result = 0;
  struct _IO_FILE *fp;
  int last_stamp;

#ifdef _IO_MTSAFE_IO
  __libc_cleanup_region_start (do_lock, flush_cleanup, NULL);
  if (do_lock)
    _IO_lock_lock (list_all_lock);
#endif

  last_stamp = _IO_list_all_stamp;
  fp = (_IO_FILE *) _IO_list_all;//这里fp取到了_IO_list_all 这里fp直接指向了_IO_2_1_stderr_首地址
  while (fp != NULL)//进入循环
    {
      run_fp = fp;
      if (do_lock)
	_IO_flockfile (fp);

      if (((fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base)
#if defined _LIBC || defined _GLIBCPP_USE_WCHAR_T
	   || (_IO_vtable_offset (fp) == 0
	       && fp->_mode > 0 && (fp->_wide_data->_IO_write_ptr
				    > fp->_wide_data->_IO_write_base))
#endif
	   )
	  && _IO_OVERFLOW (fp, EOF) == EOF)//这里经过前面的判断后调用了_IO_OVERFLOW(fp,EOF)
	result = EOF;

      if (do_lock)
	_IO_funlockfile (fp);
      run_fp = NULL;

      if (last_stamp != _IO_list_all_stamp)
	{
	  /* Something was added to the list.  Start all over again.  */
	  fp = (_IO_FILE *) _IO_list_all;
	  last_stamp = _IO_list_all_stamp;
	}
      else
	fp = fp->_chain;//这里使用FILE结构中的_chain来更新fp，直到fp为空才退出循环，所以会刷新_IO_list_all 链表中所有项的文件流
    }

#ifdef _IO_MTSAFE_IO
  if (do_lock)
    _IO_lock_unlock (list_all_lock);
  __libc_cleanup_region_end (0);
#endif

  return result;
}

查看_IO_OVERFLOW(fp, EOF)定义，以及最后的：

c 复制代码

//libc_2.23 的定义
define _IO_OVERFLOW(FP, CH) JUMP1 (__overflow, FP, CH)
define JUMP1(FUNC, THIS, X1) (_IO_JUMPS_FUNC(THIS)->FUNC) (THIS, X1)
define _IO_JUMPS_FUNC(THIS) (*(struct _IO_jump_t **) ((void *) &_IO_JUMPS_FILE_plus (THIS) + (THIS)->_vtable_offset))
    
//结合传入的参数转化后如下：相当于调用了fp的__overflow函数
define _IO_OVERFLOW(FP, CH) JUMP1 (__overflow, FP, CH)
define JUMP1(__overflow, FP, CH) (_IO_JUMPS_FUNC(FP)->__overflow) (FP, CH)
define _IO_JUMPS_FUNC(FP) (*(struct _IO_jump_t **) ((void *) &_IO_JUMPS_FILE_plus (FP) + (FP)->_vtable_offset))
    

    
//在libc_2.24后：_IO_JUMPS_FUNC的宏定义变化
define JUMP1(FUNC, THIS, X1) (_IO_JUMPS_FUNC(THIS)->FUNC) (THIS, X1)
define _IO_JUMPS_FUNC(THIS) (IO_validate_vtable (_IO_JUMPS_FILE_plus (THIS)))
    
/* Check if unknown vtable pointers are permitted; otherwise,
   terminate the process.  */
void _IO_vtable_check (void) attribute_hidden; //提前声明

/* Perform vtable pointer validation.  If validation fails, terminate
   the process.  */
static inline const struct _IO_jump_t *
IO_validate_vtable (const struct _IO_jump_t *vtable)
{
  /* Fast path: The vtable pointer is within the __libc_IO_vtables
     section.  */
  uintptr_t section_length = __stop___libc_IO_vtables - __start___libc_IO_vtables;
  const char *ptr = (const char *) vtable;
  uintptr_t offset = ptr - __start___libc_IO_vtables;
  if (__glibc_unlikely (offset >= section_length))
    /* The vtable pointer is not in the expected section.  Use the
       slow path, which will terminate the process if necessary.  */
    _IO_vtable_check ();
  return vtable;
}

void attribute_hidden _IO_vtable_check (void)
{
#ifdef SHARED
  /* Honor the compatibility flag.  */
  void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
#ifdef PTR_DEMANGLE
  PTR_DEMANGLE (flag);
#endif
  if (flag == &_IO_vtable_check)
    return;

  /* In case this libc copy is in a non-default namespace, we always
     need to accept foreign vtables because there is always a
     possibility that FILE * objects are passed across the linking
     boundary.  */
  {
    Dl_info di;
    struct link_map *l;
    if (_dl_open_hook != NULL
        || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
            && l->l_ns != LM_ID_BASE))
      return;
  }

#else /* !SHARED */
  /* We cannot perform vtable validation in the static dlopen case
     because FILE * handles might be passed back and forth across the
     boundary.  Therefore, we disable checking in this case.  */
  if (__dlopen != NULL)
    return;
#endif

  __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
}

最后找函数地址时，使用了_vtable_offset 即 _IO_FILE 结构体的 vtable 指针，而vtable 指针指向的是一个虚表，所以相当于最后调用到了下面的_IO_file_overflow函数，并且传入的参数是fp指针，即文件的地址：

随意最后IO_FILE链为：malloc报错 ==> malloc_printerr ==> __libc_message ==> abort ==> fflush ==> IO_fflush ==> _IO_flush_all ==> _IO_flush_all_lockp ==> _IO_OVERFLOW(最后使用vtable 指向的虚表中的指针)，

最后在_IO_flush_all_lockp中时有两个判断条件需要绕过，才能调用到_IO_OVERFLOW ：

fp->_mode <= 0
fp-> _IO_write_ptr > fp->_IO_write_base

所以，在unsorted bin中构造的IO_FILE 要满足这两个条件即可，最后伪造虚表，并用system地址覆盖 掉_OVERFLOW指针，并在vtable位置伪造指针 ，指向这个虚表即可。

源码调试过程

下面结合题目来调试这个过程，题目解析参考的这篇文章：House of Orange-CSDN博客，脚本和这篇文章完全一样，直接到最后一部调试malloc，直接断点到malloc：
此时堆上的布局如下，并且顺利进入malloc函数：
经过free_hook检查后进入到 _ int_malloc中分配chunk，传入的参数为main_arena地址，和申请的chunk大小：
进入 _int_malloc函数，先转化size的大小：

随后检查实际分配的大小与get_max_fast(0x80)比较，先访问fastbin：

fatbin中没有剩余的chunk，接下来就访问small bin：

small bin中也没有剩余的chunk，下面进入到unsorted bin中查询：

在unsorted bin中找到空闲chunk：

size != nb，所以先放入到small bin中：

修改后的main_arena，覆盖的IO_list_all的file中的_chain正好衔接到fake_chunk：

查看到fake_chunk中伪造的file结构：
下面会因为unsorted bin的完整性报错，从而调用malloc_printerr函数：
再调用**__libc_message**函数：
再调用abort函数：
调用发flush(NULL)，这里传入的参数是NULL：
成功进入到_IO_flush_all_lockp函数，来刷新所有文件流：

第一个文件流，被我们覆盖掉IO_list_all后，移动到了main_arena_88:

通过_chain取到第二个文件，即为我们伪造的fake_chunk：
最后成功拿到flag：