此攻击方式可以在2.34-2.36使用，至于更早的版本，本人没有使用过，看源码应该可以。
这个攻击手段主要是利用_IO_obstack_jumps，其中_IO_obstack_overflow和 _IO_obstack_xsputn 都可以触发，攻击链如下。
但实际过程中_IO_obstack_overflow容易触发assert (c != EOF); ，所以一般选择第二条链。
可以看出其中只有2个函数有赋值，其他都为空。
_IO_obstack_file只是在_IO_FILE_plus后面加了一个obstack的指针，我们可以利用错位利用法。
在刚才跳表中，仅_IO_obstack_overflow，_IO_obstack_xsputn两个函数有赋值，函数内容如下。为了避免绕过_IO_obstack_overflow中的assert (c != EOF); ，我们一般用_IO_obstack_xsputn。
简单绕过一些内容后用来触发_obstack_newchunk。
触发CALL_CHUNKFUN
显然这里使用了结构体中的指针(*(h)->chunkfun)((h)->extra_arg, (size))，并且第一个参数可控，同时需要保证(((h)->use_extra_arg)为1。
我知道很多师傅就是来抄板子的。
2.37之后取消_IO_obstack_jumps，但此链通过某种手段仍然有效。
后记：
一次偶然的机会发现，有外国友人也发现了这条链，https://nasm.re/posts/babyfile/#obstack-exploitation
本人没有抢注的意思，只是这个是我自己研究发现的，而且这条链比较简单，所以也写了出来。
_IO_obstack_overflow
obstack_1grow (obstack, c);
_obstack_newchunk (__o, 1);
new_chunk = CALL_CHUNKFUN (h, new_size);
(*(h)->chunkfun)((h)->extra_arg, (size))
_IO_obstack_overflow
obstack_1grow (obstack, c);
_obstack_newchunk (__o, 1);
new_chunk = CALL_CHUNKFUN (h, new_size);
(*(h)->chunkfun)((h)->extra_arg, (size))
_IO_obstack_xsputn
obstack_grow (obstack, data, n);;
_obstack_newchunk (__o, __len);
new_chunk = CALL_CHUNKFUN (h, new_size);
(*(h)->chunkfun)((h)->extra_arg, (size))
_IO_obstack_xsputn
obstack_grow (obstack, data, n);;
_obstack_newchunk (__o, __len);
new_chunk = CALL_CHUNKFUN (h, new_size);
(*(h)->chunkfun)((h)->extra_arg, (size))
/* the jump table. */
const struct _IO_jump_t _IO_obstack_jumps libio_vtable attribute_hidden =
{
JUMP_INIT_DUMMY,
JUMP_INIT(finish, NULL),
JUMP_INIT(overflow, _IO_obstack_overflow),
JUMP_INIT(underflow, NULL),
JUMP_INIT(uflow, NULL),
JUMP_INIT(pbackfail, NULL),
JUMP_INIT(xsputn, _IO_obstack_xsputn),
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)
};
/* the jump table. */
const struct _IO_jump_t _IO_obstack_jumps libio_vtable attribute_hidden =
{
JUMP_INIT_DUMMY,
JUMP_INIT(finish, NULL),
JUMP_INIT(overflow, _IO_obstack_overflow),
JUMP_INIT(underflow, NULL),
JUMP_INIT(uflow, NULL),
JUMP_INIT(pbackfail, NULL),
JUMP_INIT(xsputn, _IO_obstack_xsputn),
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)
};
struct _IO_obstack_file
{
struct _IO_FILE_plus file;
struct obstack *obstack;
};
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. */
/* These prototypes vary based on 'use_extra_arg', and we use
casts to the prototypeless function type in all assignments,
but having prototypes here quiets -Wstrict-prototypes. */
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
chunk contains a zero-length object. This
prevents freeing the chunk if we allocate
a bigger chunk to replace it. */
unsigned alloc_failed : 1; /* No longer used, as we now call the failed
handler on error, but retained for binary
compatibility. */
};
struct _IO_obstack_file
{
struct _IO_FILE_plus file;
struct obstack *obstack;
};
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. */
/* These prototypes vary based on 'use_extra_arg', and we use
casts to the prototypeless function type in all assignments,
but having prototypes here quiets -Wstrict-prototypes. */
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
chunk contains a zero-length object. This
prevents freeing the chunk if we allocate
a bigger chunk to replace it. */
unsigned alloc_failed : 1; /* No longer used, as we now call the failed
handler on error, but retained for binary
compatibility. */
};
static int _IO_obstack_overflow (FILE *fp, int c)
{
struct obstack *obstack = ((struct _IO_obstack_file *) fp)->obstack;
int size;
/* Make room for another character. This might as well allocate a
new chunk a memory and moves the old contents over. */
assert (c != EOF); // 此处不可控
obstack_1grow (obstack, c);
/* Setup the buffer pointers again. */
fp->_IO_write_base = obstack_base (obstack);
fp->_IO_write_ptr = obstack_next_free (obstack);
size = obstack_room (obstack);
fp->_IO_write_end = fp->_IO_write_ptr + size;
/* Now allocate the rest of the current chunk. */
obstack_blank_fast (obstack, size);
return c;
}
static int _IO_obstack_overflow (FILE *fp, int c)
{
struct obstack *obstack = ((struct _IO_obstack_file *) fp)->obstack;
int size;
/* Make room for another character. This might as well allocate a
new chunk a memory and moves the old contents over. */
assert (c != EOF); // 此处不可控
obstack_1grow (obstack, c);
/* Setup the buffer pointers again. */
fp->_IO_write_base = obstack_base (obstack);
fp->_IO_write_ptr = obstack_next_free (obstack);
size = obstack_room (obstack);
fp->_IO_write_end = fp->_IO_write_ptr + size;
/* Now allocate the rest of the current chunk. */
obstack_blank_fast (obstack, size);
return c;
}
static size_t _IO_obstack_xsputn (FILE *fp, const void *data, size_t n)
{
struct obstack *obstack = ((struct _IO_obstack_file *) fp)->obstack;
if (fp->_IO_write_ptr + n > fp->_IO_write_end)
{
int size;
/* We need some more memory. First shrink the buffer to the
space we really currently need. */
obstack_blank_fast (obstack, fp->_IO_write_ptr - fp->_IO_write_end);
/* Now grow for N bytes, and put the data there. */
obstack_grow (obstack, data, n); //执行次函数
/* Setup the buffer pointers again. */
fp->_IO_write_base = obstack_base (obstack);
fp->_IO_write_ptr = obstack_next_free (obstack);
size = obstack_room (obstack);
fp->_IO_write_end = fp->_IO_write_ptr + size;
/* Now allocate the rest of the current chunk. */
obstack_blank_fast (obstack, size);
}
else
fp->_IO_write_ptr = __mempcpy (fp->_IO_write_ptr, data, n);
return n;
}
static size_t _IO_obstack_xsputn (FILE *fp, const void *data, size_t n)
{
struct obstack *obstack = ((struct _IO_obstack_file *) fp)->obstack;
if (fp->_IO_write_ptr + n > fp->_IO_write_end)
{
int size;
/* We need some more memory. First shrink the buffer to the
space we really currently need. */
obstack_blank_fast (obstack, fp->_IO_write_ptr - fp->_IO_write_end);
/* Now grow for N bytes, and put the data there. */
obstack_grow (obstack, data, n); //执行次函数
/* Setup the buffer pointers again. */
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最后于 2023-3-15 08:30
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，原因： 错字
