glibc/libio/vasprintf.c
Florian Weimer 7b52c8ae05 libio: Avoid _allocate_buffer, _free_buffer function pointers [BZ #23236]
These unmangled function pointers reside on the heap and could
be targeted by exploit writers, effectively bypassing libio vtable
validation.  Instead, we ignore these pointers and always call
malloc or free.

In theory, this is a backwards-incompatible change, but using the
global heap instead of the user-supplied callback functions should
have little application impact.  (The old libstdc++ implementation
exposed this functionality via a public, undocumented constructor
in its strstreambuf class.)

(cherry picked from commit 4e8a6346cd)
2018-06-01 11:24:58 +02:00

89 lines
3.2 KiB
C

/* Copyright (C) 1995-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>.
As a special exception, if you link the code in this file with
files compiled with a GNU compiler to produce an executable,
that does not cause the resulting executable to be covered by
the GNU Lesser General Public License. This exception does not
however invalidate any other reasons why the executable file
might be covered by the GNU Lesser General Public License.
This exception applies to code released by its copyright holders
in files containing the exception. */
#include <malloc.h>
#include <string.h>
#include "libioP.h"
#include "stdio.h"
#include <stdio_ext.h>
#include "strfile.h"
int
_IO_vasprintf (char **result_ptr, const char *format, _IO_va_list args)
{
/* Initial size of the buffer to be used. Will be doubled each time an
overflow occurs. */
const _IO_size_t init_string_size = 100;
char *string;
_IO_strfile sf;
int ret;
_IO_size_t needed;
_IO_size_t allocated;
/* No need to clear the memory here (unlike for open_memstream) since
we know we will never seek on the stream. */
string = (char *) malloc (init_string_size);
if (string == NULL)
return -1;
#ifdef _IO_MTSAFE_IO
sf._sbf._f._lock = NULL;
#endif
_IO_no_init (&sf._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
_IO_JUMPS (&sf._sbf) = &_IO_str_jumps;
_IO_str_init_static_internal (&sf, string, init_string_size, string);
sf._sbf._f._flags &= ~_IO_USER_BUF;
sf._s._allocate_buffer_unused = (_IO_alloc_type) malloc;
sf._s._free_buffer_unused = (_IO_free_type) free;
ret = _IO_vfprintf (&sf._sbf._f, format, args);
if (ret < 0)
{
free (sf._sbf._f._IO_buf_base);
return ret;
}
/* Only use realloc if the size we need is of the same (binary)
order of magnitude then the memory we allocated. */
needed = sf._sbf._f._IO_write_ptr - sf._sbf._f._IO_write_base + 1;
allocated = sf._sbf._f._IO_write_end - sf._sbf._f._IO_write_base;
if ((allocated >> 1) <= needed)
*result_ptr = (char *) realloc (sf._sbf._f._IO_buf_base, needed);
else
{
*result_ptr = (char *) malloc (needed);
if (*result_ptr != NULL)
{
memcpy (*result_ptr, sf._sbf._f._IO_buf_base, needed - 1);
free (sf._sbf._f._IO_buf_base);
}
else
/* We have no choice, use the buffer we already have. */
*result_ptr = (char *) realloc (sf._sbf._f._IO_buf_base, needed);
}
if (*result_ptr == NULL)
*result_ptr = sf._sbf._f._IO_buf_base;
(*result_ptr)[needed - 1] = '\0';
return ret;
}
ldbl_weak_alias (_IO_vasprintf, vasprintf)