前言
原本以为只学习house of apple2就足以应对所有高版本了，但是还是被白名单制裁了，这里浅析一下house of cat以弥补apple2的缺陷。
house of cat预计分三个部分来讲解，这篇是源码原理分析。中篇主要讲解源码调试和一些在本篇里没有讲解到的小细节绕过，下篇主要讲解例题。
我个人认为house of cat最大的用处是在程序没有exit函数和使用白名单过滤，并且我们只能利用largbinattack的时候。本次源码分析也是基于glibc-2.35。
house of cat
前置知识：
_IO_wfile_jumps
const struct _IO_jump_t _IO_wfile_jumps =
{
JUMP_INIT_DUMMY,
JUMP_INIT(finish, _IO_new_file_finish),
JUMP_INIT(overflow, (_IO_overflow_t) _IO_wfile_overflow),
JUMP_INIT(underflow, (_IO_underflow_t) _IO_wfile_underflow),
JUMP_INIT(uflow, (_IO_underflow_t) _IO_wdefault_uflow),
JUMP_INIT(pbackfail, (_IO_pbackfail_t) _IO_wdefault_pbackfail),
JUMP_INIT(xsputn, _IO_wfile_xsputn),
JUMP_INIT(xsgetn, _IO_file_xsgetn),
JUMP_INIT(seekoff, _IO_wfile_seekoff),
JUMP_INIT(seekpos, _IO_default_seekpos),
JUMP_INIT(setbuf, _IO_new_file_setbuf),
JUMP_INIT(sync, (_IO_sync_t) _IO_wfile_sync),
JUMP_INIT(doallocate, _IO_wfile_doallocate),
JUMP_INIT(read, _IO_file_read),
JUMP_INIT(write, _IO_new_file_write),
JUMP_INIT(seek, _IO_file_seek),
JUMP_INIT(close, _IO_file_close),
JUMP_INIT(stat, _IO_file_stat),
JUMP_INIT(showmanyc, _IO_default_showmanyc),
JUMP_INIT(imbue, _IO_default_imbue)
};在house of apple2内我们利用的是：
JUMP_INIT(underflow, (_IO_underflow_t) _IO_wfile_underflow)house of cat利用的则是：
JUMP_INIT(seekoff, _IO_wfile_seekoff),我们来看看这个函数：
_IO_wfile_seekoff
off64_t
_IO_wfile_seekoff (FILE *fp, off64_t offset, int dir, int mode)
{
off64_t result;
off64_t delta, new_offset;
long int count;
/*短路变成一个单独的功能。 我们不想混合任何功能，也不想触及 FILE 对象内部的任何内容。*/
if (mode == 0)
return do_ftell_wide (fp);
/* POSIX.1 8.2.3.7 says that after a call the fflush() the file
offset of the underlying file must be exact. */
int must_be_exact = ((fp->_wide_data->_IO_read_base
== fp->_wide_data->_IO_read_end)
&& (fp->_wide_data->_IO_write_base
== fp->_wide_data->_IO_write_ptr));
bool was_writing = ((fp->_wide_data->_IO_write_ptr
> fp->_wide_data->_IO_write_base)
|| _IO_in_put_mode (fp));
/*刷新未写入的字符。（如果我们在缓冲区内查找，这可能会执行不必要的写入。但是为了能够切换到阅读，我们需要将 egptr 设置为 pptr。 这在当前的设计中是无法做到的，它假设 file_ptr（） 是 eGptr。 无论如何，由于我们可能在close()时最终刷新，因此没有太大区别。FIXME：模拟内存映射文件。*/
if (was_writing && _IO_switch_to_wget_mode (fp))
return WEOF;
if (fp->_wide_data->_IO_buf_base == NULL)
{
/* It could be that we already have a pushback buffer. */
if (fp->_wide_data->_IO_read_base != NULL)
{
free (fp->_wide_data->_IO_read_base);
fp->_flags &= ~_IO_IN_BACKUP;
}
_IO_doallocbuf (fp);
_IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_wsetp (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base);
_IO_wsetg (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base, fp->_wide_data->_IO_buf_base);
}
switch (dir)
{
struct _IO_codecvt *cv;
int clen;
case _IO_seek_cur:
/*调整预读（字节是缓冲区）。 为此，我们必须找出外部缓冲区中的哪个位置对应于内部缓冲区中的当前位置。*/
cv = fp->_codecvt;
clen = __libio_codecvt_encoding (cv);
if (mode != 0 || !was_writing)
{
if (clen > 0)
{
offset -= (fp->_wide_data->_IO_read_end
- fp->_wide_data->_IO_read_ptr) * clen;
/* Adjust by readahead in external buffer. */
offset -= fp->_IO_read_end - fp->_IO_read_ptr;
}
else
{
int nread;
delta = (fp->_wide_data->_IO_read_ptr
- fp->_wide_data->_IO_read_base);
fp->_wide_data->_IO_state = fp->_wide_data->_IO_last_state;
nread = __libio_codecvt_length (cv,
&fp->_wide_data->_IO_state,
fp->_IO_read_base,
fp->_IO_read_end, delta);
fp->_IO_read_ptr = fp->_IO_read_base + nread;
fp->_wide_data->_IO_read_end = fp->_wide_data->_IO_read_ptr;
offset -= fp->_IO_read_end - fp->_IO_read_base - nread;
}
}
if (fp->_offset == _IO_pos_BAD)
goto dumb;
/* Make offset absolute, assuming current pointer is file_ptr(). */
offset += fp->_offset;
dir = _IO_seek_set;
break;
case _IO_seek_set:
break;
case _IO_seek_end:
{
struct __stat64_t64 st;
if (_IO_SYSSTAT (fp, &st) == 0 && S_ISREG (st.st_mode))
{
offset += st.st_size;
dir = _IO_seek_set;
}
else
goto dumb;
}
}
_IO_free_wbackup_area (fp);
/* At this point, dir==_IO_seek_set. */
/*如果目标在当前缓冲区内，请优化：*/
if (fp->_offset != _IO_pos_BAD && fp->_IO_read_base != NULL
&& !_IO_in_backup (fp))
{
off64_t start_offset = (fp->_offset
- (fp->_IO_read_end - fp->_IO_buf_base));
if (offset >= start_offset && offset < fp->_offset)
{
_IO_setg (fp, fp->_IO_buf_base,
fp->_IO_buf_base + (offset - start_offset),
fp->_IO_read_end);
_IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_wsetg (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base);
_IO_wsetp (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base);
if (adjust_wide_data (fp, false))
goto dumb;
_IO_mask_flags (fp, 0, _IO_EOF_SEEN);
goto resync;
}
}
if (fp->_flags & _IO_NO_READS)
goto dumb;
/*尝试寻求块边界，以改善内核页面管理。*/
new_offset = offset & ~(fp->_IO_buf_end - fp->_IO_buf_base - 1);
delta = offset - new_offset;
if (delta > fp->_IO_buf_end - fp->_IO_buf_base)
{
new_offset = offset;
delta = 0;
}
result = _IO_SYSSEEK (fp, new_offset, 0);
if (result < 0)
return EOF;
if (delta == 0)
count = 0;
else
{
count = _IO_SYSREAD (fp, fp->_IO_buf_base,
(must_be_exact
? delta : fp->_IO_buf_end - fp->_IO_buf_base));
if (count < delta)
{
/*我们不被允许阅读，但试着寻找剩下的。*/
offset = count == EOF ? delta : delta-count;
dir = _IO_seek_cur;
goto dumb;
}
}
_IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base + delta,
fp->_IO_buf_base + count);
_IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_wsetg (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base, fp->_wide_data->_IO_buf_base);
_IO_wsetp (fp, fp->_wide_data->_IO_buf_base, fp->_wide_data->_IO_buf_base);
if (adjust_wide_data (fp, true))
goto dumb;
fp->_offset = result + count;
_IO_mask_flags (fp, 0, _IO_EOF_SEEN);
return offset;
dumb:
_IO_unsave_markers (fp);
result = _IO_SYSSEEK (fp, offset, dir);
if (result != EOF)
{
_IO_mask_flags (fp, 0, _IO_EOF_SEEN);
fp->_offset = result;
_IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_setp (fp, fp->_IO_buf_base, fp->_IO_buf_base);
_IO_wsetg (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base, fp->_wide_data->_IO_buf_base);
_IO_wsetp (fp, fp->_wide_data->_IO_buf_base,
fp->_wide_data->_IO_buf_base);
}
return result;
resync:
/*我们需要这样做，因为内核中的文件偏移量可能会在我们背后发生更改。当我们打开一个文件，然后进行分叉时，可能会发生这种情况。
一个进程可能会访问该文件，内核文件的偏移量将发生变化。*/
if (fp->_offset >= 0)
_IO_SYSSEEK (fp, fp->_offset, 0);
return offset;
}这里我们只关注两个地方就可以了：
，也就是说我们只要让传入的mode不为0，就能正常进行到_IO_switch_to_wget_mode (fp)这个函数。
_IO_switch_to_wget_mode()
int
_IO_switch_to_wget_mode (FILE *fp)
{
if (fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_write_base)
if ((wint_t)_IO_WOVERFLOW (fp, WEOF) == WEOF)
return EOF;
if (_IO_in_backup (fp))
fp->_wide_data->_IO_read_base = fp->_wide_data->_IO_backup_base;
else
{
fp->_wide_data->_IO_read_base = fp->_wide_data->_IO_buf_base;
if (fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_read_end)
fp->_wide_data->_IO_read_end = fp->_wide_data->_IO_write_ptr;
}
fp->_wide_data->_IO_read_ptr = fp->_wide_data->_IO_write_ptr;
fp->_wide_data->_IO_write_base = fp->_wide_data->_IO_write_ptr
= fp->_wide_data->_IO_write_end = fp->_wide_data->_IO_read_ptr;
fp->_flags &= ~_IO_CURRENTLY_PUTTING;
return 0;
}学习过house of apple2过后，我们应该能看到一个我们非常喜爱的函数：
就是说只需要满足fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_write_base就能控制执行流了。
__malloc_assert
因为存在exit函数，那不如去打apple2，所以这里只讨论一下其他触发方式。
_malloc_assert函数，他会根据vtable表如_IO_xxx_jumps调用IO等相关函数；该函数最终会根据stderr这个IO结构体进行相关的IO操作。
static void
__malloc_assert (const char *assertion, const char *file, unsigned int line,
const char *function)
{
(void) __fxprintf (NULL, "%s%s%s:%u: %s%sAssertion `%s' failed.\n",
__progname, __progname[0] ? ": " : "",
file, line,
function ? function : "", function ? ": " : "",
assertion);
fflush (stderr);
abort ();
}__fxprintf()
来看看 __fxprintf()这个函数，
int
__fxprintf (FILE *fp, const char *fmt, ...)
{
va_list ap;
va_start (ap, fmt);
int res = __vfxprintf (fp, fmt, ap, 0);
va_end (ap);
return res;
}__vfxprintf()
接着走下去，看__vfxprintf()函数，
int
__vfxprintf (FILE *fp, const char *fmt, va_list ap,
unsigned int mode_flags)
{
if (fp == NULL)
fp = stderr;
_IO_flockfile (fp);
int res = locked_vfxprintf (fp, fmt, ap, mode_flags);
_IO_funlockfile (fp);
return res;
}locked_vfxprintf
static int
locked_vfxprintf (FILE *fp, const char *fmt, va_list ap,
unsigned int mode_flags)
{
if (_IO_fwide (fp, 0) <= 0)
return __vfprintf_internal (fp, fmt, ap, mode_flags);
/* We must convert the narrow format string to a wide one.
Each byte can produce at most one wide character. */
wchar_t *wfmt;
mbstate_t mbstate;
int res;
int used_malloc = 0;
size_t len = strlen (fmt) + 1;
if (__glibc_unlikely (len > SIZE_MAX / sizeof (wchar_t)))
{
__set_errno (EOVERFLOW);
return -1;
}
if (__libc_use_alloca (len * sizeof (wchar_t)))
wfmt = alloca (len * sizeof (wchar_t));
else if ((wfmt = malloc (len * sizeof (wchar_t))) == NULL)
return -1;
else
used_malloc = 1;
memset (&mbstate, 0, sizeof mbstate);
res = __mbsrtowcs (wfmt, &fmt, len, &mbstate);
if (res != -1)
res = __vfwprintf_internal (fp, wfmt, ap, mode_flags);
if (used_malloc)
free (wfmt);
return res;
}
这里我们让他去走__vfprintf_internal这个函数就好。
__vfprintf_internal：
这个函数实际上是__vfprintf_internal.c文件内的vfprintf。具体原因我也不是很清楚，有大佬知道的话可以评论区讲解一下。
这个函数的实现有点长，不想细读的可以看下一个代码块。
int
vfprintf (FILE *s, const CHAR_T *format, va_list ap, unsigned int mode_flags)
{
/* The character used as thousands separator. */
THOUSANDS_SEP_T thousands_sep = 0;
/* The string describing the size of groups of digits. */
const char *grouping;
/* Place to accumulate the result. */
int done;
/* Current character in format string. */
const UCHAR_T *f;
/* End of leading constant string. */
const UCHAR_T *lead_str_end;
/* Points to next format specifier. */
const UCHAR_T *end_of_spec;
/* Buffer intermediate results. */
CHAR_T work_buffer[WORK_BUFFER_SIZE];
CHAR_T *workend;
/* We have to save the original argument pointer. */
va_list ap_save;
/* Count number of specifiers we already processed. */
int nspecs_done;
/* For the %m format we may need the current `errno' value. */
int save_errno = errno;
/* 1 if format is in read-only memory, -1 if it is in writable memory,
0 if unknown. */
int readonly_format = 0;
/* Orient the stream. */
#ifdef ORIENT
ORIENT;
#endif
/* Sanity check of arguments. */
ARGCHECK (s, format);
#ifdef ORIENT
/* Check for correct orientation. */
if (_IO_vtable_offset (s) == 0
&& _IO_fwide (s, sizeof (CHAR_T) == 1 ? -1 : 1)
!= (sizeof (CHAR_T) == 1 ? -1 : 1))
/* The stream is already oriented otherwise. */
return EOF;
#endif
if (UNBUFFERED_P (s))
/* Use a helper function which will allocate a local temporary buffer
for the stream and then call us again. */
return buffered_vfprintf (s, format, ap, mode_flags);
/* Initialize local variables. */
done = 0;
grouping = (const char *) -1;
#ifdef __va_copy
/* This macro will be available soon in gcc's <stdarg.h>. We need it
since on some systems `va_list' is not an integral type. */
__va_copy (ap_save, ap);
#else
ap_save = ap;
#endif
nspecs_done = 0;
#ifdef COMPILE_WPRINTF
/* Find the first format specifier. */
f = lead_str_end = __find_specwc ((const UCHAR_T *) format);
#else
/* Find the first format specifier. */
f = lead_str_end = __find_specmb ((const UCHAR_T *) format);
#endif
/* Lock stream. */
_IO_cleanup_region_start ((void (*) (void *)) &_IO_funlockfile, s);
_IO_flockfile (s);
/* Write the literal text before the first format. */
outstring ((const UCHAR_T *) format,
lead_str_end - (const UCHAR_T *) format);
/* If we only have to print a simple string, return now. */
if (*f == L_('\0'))
goto all_done;
/* Use the slow path in case any printf handler is registered. */
if (__glibc_unlikely (__printf_function_table != NULL
|| __printf_modifier_table != NULL
|| __printf_va_arg_table != NULL))
goto do_positional;
/* Process whole format string. */
do
{
STEP0_3_TABLE;
STEP4_TABLE;
int is_negative; /* Flag for negative number. */
union
{
unsigned long long int longlong;
unsigned long int word;
} number;
int base;
union printf_arg the_arg;
CHAR_T *string; /* Pointer to argument string. */
int alt = 0; /* Alternate format. */
int space = 0; /* Use space prefix if no sign is needed. */
int left = 0; /* Left-justify output. */
int showsign = 0; /* Always begin with plus or minus sign. */
int group = 0; /* Print numbers according grouping rules. */
/* Argument is long double/long long int. Only used if
double/long double or long int/long long int are distinct. */
int is_long_double __attribute__ ((unused)) = 0;
int is_short = 0; /* Argument is short int. */
int is_long = 0; /* Argument is long int. */
int is_char = 0; /* Argument is promoted (unsigned) char. */
int width = 0; /* Width of output; 0 means none specified. */
int prec = -1; /* Precision of output; -1 means none specified. */
/* This flag is set by the 'I' modifier and selects the use of the
`outdigits' as determined by the current locale. */
int use_outdigits = 0;
UCHAR_T pad = L_(' ');/* Padding character. */
CHAR_T spec;
workend = work_buffer + WORK_BUFFER_SIZE;
/* Get current character in format string. */
JUMP (*++f, step0_jumps);
/* ' ' flag. */
LABEL (flag_space):
space = 1;
JUMP (*++f, step0_jumps);
/* '+' flag. */
LABEL (flag_plus):
showsign = 1;
JUMP (*++f, step0_jumps);
/* The '-' flag. */
LABEL (flag_minus):
left = 1;
pad = L_(' ');
JUMP (*++f, step0_jumps);
/* The '#' flag. */
LABEL (flag_hash):
alt = 1;
JUMP (*++f, step0_jumps);
/* The '0' flag. */
LABEL (flag_zero):
if (!left)
pad = L_('0');
JUMP (*++f, step0_jumps);
/* The '\'' flag. */
LABEL (flag_quote):
group = 1;
if (grouping == (const char *) -1)
{
#ifdef COMPILE_WPRINTF
thousands_sep = _NL_CURRENT_WORD (LC_NUMERIC,
_NL_NUMERIC_THOUSANDS_SEP_WC);
#else
thousands_sep = _NL_CURRENT (LC_NUMERIC, THOUSANDS_SEP);
#endif
grouping = _NL_CURRENT (LC_NUMERIC, GROUPING);
if (*grouping == '\0' || *grouping == CHAR_MAX
#ifdef COMPILE_WPRINTF
|| thousands_sep == L'\0'
#else
|| *thousands_sep == '\0'
#endif
)
grouping = NULL;
}
JUMP (*++f, step0_jumps);
LABEL (flag_i18n):
use_outdigits = 1;
JUMP (*++f, step0_jumps);
/* Get width from argument. */
LABEL (width_asterics):
{
const UCHAR_T *tmp; /* Temporary value. */
tmp = ++f;
if (ISDIGIT (*tmp))
{
int pos = read_int (&tmp);
if (pos == -1)
{
__set_errno (EOVERFLOW);
done = -1;
goto all_done;
}
if (pos && *tmp == L_('$'))
/* The width comes from a positional parameter. */
goto do_positional;
}
width = va_arg (ap, int);
/* Negative width means left justified. */
if (width < 0)
{
width = -width;
pad = L_(' ');
left = 1;
}
}
JUMP (*f, step1_jumps);
/* Given width in format string. */
LABEL (width):
width = read_int (&f);
if (__glibc_unlikely (width == -1))
{
__set_errno (EOVERFLOW);
done = -1;
goto all_done;
}
if (*f == L_('$'))
/* Oh, oh. The argument comes from a positional parameter. */
goto do_positional;
JUMP (*f, step1_jumps);
LABEL (precision):
++f;
if (*f == L_('*'))
{
const UCHAR_T *tmp; /* Temporary value. */
tmp = ++f;
if (ISDIGIT (*tmp))
{
int pos = read_int (&tmp);
if (pos == -1)
{
__set_errno (EOVERFLOW);
done = -1;
goto all_done;
}
if (pos && *tmp == L_('$'))
/* The precision comes from a positional parameter. */
goto do_positional;
}
prec = va_arg (ap, int);
/* If the precision is negative the precision is omitted. */
if (prec < 0)
prec = -1;
}
else if (ISDIGIT (*f))
{
prec = read_int (&f);
/* The precision was specified in this case as an extremely
large positive value. */
if (prec == -1)
{
__set_errno (EOVERFLOW);
done = -1;
goto all_done;
}
}
else
prec = 0;
JUMP (*f, step2_jumps);
/* Process 'h' modifier. There might another 'h' following. */
LABEL (mod_half):
is_short = 1;
JUMP (*++f, step3a_jumps);
/* Process 'hh' modifier. */
LABEL (mod_halfhalf):
is_short = 0;
is_char = 1;
JUMP (*++f, step4_jumps);
/* Process 'l' modifier. There might another 'l' following. */
LABEL (mod_long):
is_long = 1;
JUMP (*++f, step3b_jumps);
/* Process 'L', 'q', or 'll' modifier. No other modifier is
allowed to follow. */
LABEL (mod_longlong):
is_long_double = 1;
is_long = 1;
JUMP (*++f, step4_jumps);
LABEL (mod_size_t):
is_long_double = sizeof (size_t) > sizeof (unsigned long int);
is_long = sizeof (size_t) > sizeof (unsigned int);
JUMP (*++f, step4_jumps);
LABEL (mod_ptrdiff_t):
is_long_double = sizeof (ptrdiff_t) > sizeof (unsigned long int);
is_long = sizeof (ptrdiff_t) > sizeof (unsigned int);
JUMP (*++f, step4_jumps);
LABEL (mod_intmax_t):
is_long_double = sizeof (intmax_t) > sizeof (unsigned long int);
is_long = sizeof (intmax_t) > sizeof (unsigned int);
JUMP (*++f, step4_jumps);
/* Process current format. */
while (1)
{
#define process_arg_int() va_arg (ap, int)
#define process_arg_long_int() va_arg (ap, long int)
#define process_arg_long_long_int() va_arg (ap, long long int)
#define process_arg_pointer() va_arg (ap, void *)
#define process_arg_string() va_arg (ap, const char *)
#define process_arg_unsigned_int() va_arg (ap, unsigned int)
#define process_arg_unsigned_long_int() va_arg (ap, unsigned long int)
#define process_arg_unsigned_long_long_int() va_arg (ap, unsigned long long int)
#define process_arg_wchar_t() va_arg (ap, wchar_t)
#define process_arg_wstring() va_arg (ap, const wchar_t *)
process_arg ();
process_string_arg ();
#undef process_arg_int
#undef process_arg_long_int
#undef process_arg_long_long_int
#undef process_arg_pointer
#undef process_arg_string
#undef process_arg_unsigned_int
#undef process_arg_unsigned_long_int
#undef process_arg_unsigned_long_long_int
#undef process_arg_wchar_t
#undef process_arg_wstring
LABEL (form_float):
LABEL (form_floathex):
{
if (__glibc_unlikely ((mode_flags & PRINTF_LDBL_IS_DBL) != 0))
is_long_double = 0;
struct printf_info info =
{
.prec = prec,
.width = width,
.spec = spec,
.is_long_double = is_long_double,
.is_short = is_short,
.is_long = is_long,
.alt = alt,
.space = space,
.left = left,
.showsign = showsign,
.group = group,
.pad = pad,
.extra = 0,
.i18n = use_outdigits,
.wide = sizeof (CHAR_T) != 1,
.is_binary128 = 0
};
PARSE_FLOAT_VA_ARG_EXTENDED (info);
const void *ptr = &the_arg;
int function_done = __printf_fp_spec (s, &info, &ptr);
if (function_done < 0)
{
done = -1;
goto all_done;
}
done_add (function_done);
}
break;
LABEL (form_unknown):
if (spec == L_('\0'))
{
/* The format string ended before the specifier is complete. */
__set_errno (EINVAL);
done = -1;
goto all_done;
}
/* If we are in the fast loop force entering the complicated
one. */
goto do_positional;
}
/* The format is correctly handled. */
++nspecs_done;
/* Look for next format specifier. */
#ifdef COMPILE_WPRINTF
f = __find_specwc ((end_of_spec = ++f));
#else
f = __find_specmb ((end_of_spec = ++f));
#endif
/* Write the following constant string. */
outstring (end_of_spec, f - end_of_spec);
}
while (*f != L_('\0'));
/* Unlock stream and return. */
goto all_done;
/* Hand off processing for positional parameters. */
do_positional:
done = printf_positional (s, format, readonly_format, ap, &ap_save,
done, nspecs_done, lead_str_end, work_buffer,
save_errno, grouping, thousands_sep, mode_flags);
all_done:
/* Unlock the stream. */
_IO_funlockfile (s);
_IO_cleanup_region_end (0);
return done;
}上面这个函数我们只需要知道他最终是去调用了vtable指针_IO_wfile_jumps所指向的结构体中的_IO_file_xsputn，那我们只需要将vtable处的_IO_wfile_jumps+0x10就能顺利调用到_IO_wfile_seekoff 这个函数了。
后面就是类似于apple2的执行流程，通过vtable处的_IO_wfile_jumps去跳转执行_IO_wfile_seekoff 这个函数， 最终执行到_IO_switch_to_wget_mode()内的_IO_WOVERFLOW的宏定义。
总结：
函数执行流：
__malloc_assert -->> __fxprintf() -->> __vfxprintf() -->> locked_vfxprintf()
-->> _IO_wfile_jumps -->> _IO_wfile_seekoff -->> _IO_switch_to_wget_mode()
-->> _IO_WOVERFLOW绕过总结：
- fp.mode != 0
-
fp->_mode <= 0 && fp->_IO_write_ptr > fp->_IO_write_base 或者 _IO_vtable_offset (fp) == 0 && fp->_mode > 0 && (fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_write_base)
-
fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_write_base
当然这里面有个小细节：
从FSOP的角度去看，我们希望去调用到 _IO_wfile_seekoff这个函数，那么我们对于vtable的设置应该设置为_IO_wfile_jumps+0x30，但是在走__malloc_assert这条调用链时，我们只需要设置为_IO_wfile_jumps+0x10
怎么触发__malloc_assert？
这个函数的调用链为：_int_malloc --->> sysmalloc --->> __malloc_assert
_int_malloc这个也是一个大家伙，只看调用sysmalloc的地方：
点进去查看sysmalloc函数内的调用__malloc_assert()代码段：
检测条件
- old_size >= 0x20;
- old_top.prev_inuse = 0;
- old_top页对齐
也就是说，我们只要满足这三个条件中的任何一个就可以触发了。
到这里上篇就结束了。如有错误，欢迎评论区指出，谢谢！
标签：fp,wide,int,house,cat,base,IO,data,浅析 From： https://blog.csdn.net/2301_79327647/article/details/141166770