IO FILE相关

IO_FILE相关

Orz 最近碰到的几道题都是用到了它，出师不利2333

IO_FILE相关结构

覆盖 _IO_list_all (全局变量) 指向伪造的结构，然后改写 vtable 指针来 getshell

FILE 结构在程序执行 fopen 的时候动态创建并且分配在堆中

_IO_FILE 结构体

struct _IO_FILE {
  int _flags;       /* High-order word is _IO_MAGIC; rest is flags. */
#define _IO_file_flags _flags
  /* The following pointers correspond to the C++ streambuf protocol. */
  /* Note:  Tk uses the _IO_read_ptr and _IO_read_end fields directly. */
  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;   /* Start of reserve area. */
  char* _IO_buf_end;    /* End of reserve area. */
  /* 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;

  int _fileno;
#if 0
  int _blksize;
#else
  int _flags2;
#endif
  _IO_off_t _old_offset; /* This used to be _offset but it's too small.  */

#define __HAVE_COLUMN /* temporary */
  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];

  /*  char* _save_gptr;  char* _save_egptr; */

  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};

然后通过 _chain 连接成一个链表，全局变量 _IO_list_all 指向链表头部

实际上在 IO_FILE 结构体是包含在一个叫 _IO_FILE_plus 中的

struct _IO_FILE_plus
{
    _IO_FILE    file;
    IO_jump_t   *vtable;
}

里面还有个 IO_jump_t 类型的指针 vtable

struct _IO_jump_t
{
    JUMP_FIELD(size_t, __dummy);
    JUMP_FIELD(size_t, __dummy2);
    JUMP_FIELD(_IO_finish_t, __finish);
    JUMP_FIELD(_IO_overflow_t, __overflow);
    JUMP_FIELD(_IO_underflow_t, __underflow);
    JUMP_FIELD(_IO_underflow_t, __uflow);
    JUMP_FIELD(_IO_pbackfail_t, __pbackfail);
    /* showmany */
    JUMP_FIELD(_IO_xsputn_t, __xsputn);
    JUMP_FIELD(_IO_xsgetn_t, __xsgetn);
    JUMP_FIELD(_IO_seekoff_t, __seekoff);
    JUMP_FIELD(_IO_seekpos_t, __seekpos);
    JUMP_FIELD(_IO_setbuf_t, __setbuf);
    JUMP_FIELD(_IO_sync_t, __sync);
    JUMP_FIELD(_IO_doallocate_t, __doallocate);
    JUMP_FIELD(_IO_read_t, __read);
    JUMP_FIELD(_IO_write_t, __write);
    JUMP_FIELD(_IO_seek_t, __seek);
    JUMP_FIELD(_IO_close_t, __close);
    JUMP_FIELD(_IO_stat_t, __stat);
    JUMP_FIELD(_IO_showmanyc_t, __showmanyc);
    JUMP_FIELD(_IO_imbue_t, __imbue);
#if 0
    get_column;
    set_column;
#endif
};

伪造 vtable 劫持程序流程

linux 中常见的 IO 函数都需要经过 FILE 结构体进行处理，尤其是 IO_FILE_plus 结构体中的 vtable，一些函数会取出 vtable 中的指针进行调用

所以这种攻击方法的核心思想是：对 _IO_FILE_plus 的 vtable 动手脚，通过把 vtable 指向我们控制的内存，并在其中布置函数指针来实现

攻击方法有两种：一种是通过任意地址写改写 vtable 中的函数指针

一种是覆盖 vtable 的指针指向我们控制的内存，然后在上面布置函数指针

FSOP

前面的 house of orange 用的就是这种方法来 getshell 的

https://www.yuque.com/go/doc/13562282

原文: https://www.yuque.com/hxfqg9/bin/sr9dcu