glibc/libio/vsnprintf.c
Florian Weimer db3476aff1 libio: Implement vtable verification [BZ #20191]
This commit puts all libio vtables in a dedicated, read-only ELF
section, so that they are consecutive in memory.  Before any indirect
jump, the vtable pointer is checked against the section boundaries,
and the process is terminated if the vtable pointer does not fall into
the special ELF section.

To enable backwards compatibility, a special flag variable
(_IO_accept_foreign_vtables), protected by the pointer guard, avoids
process termination if libio stream object constructor functions have
been called earlier.  Such constructor functions are called by the GCC
2.95 libstdc++ library, and this mechanism ensures compatibility with
old binaries.  Existing callers inside glibc of these functions are
adjusted to call the original functions, not the wrappers which enable
vtable compatiblity.

The compatibility mechanism is used to enable passing FILE * objects
across a static dlopen boundary, too.
2016-06-23 20:01:52 +02:00

122 lines
4.2 KiB
C

/* Copyright (C) 1994-2016 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 "libioP.h"
#include "strfile.h"
static int _IO_strn_overflow (_IO_FILE *fp, int c) __THROW;
static int
_IO_strn_overflow (_IO_FILE *fp, int c)
{
/* When we come to here this means the user supplied buffer is
filled. But since we must return the number of characters which
would have been written in total we must provide a buffer for
further use. We can do this by writing on and on in the overflow
buffer in the _IO_strnfile structure. */
_IO_strnfile *snf = (_IO_strnfile *) fp;
if (fp->_IO_buf_base != snf->overflow_buf)
{
/* Terminate the string. We know that there is room for at
least one more character since we initialized the stream with
a size to make this possible. */
*fp->_IO_write_ptr = '\0';
_IO_setb (fp, snf->overflow_buf,
snf->overflow_buf + sizeof (snf->overflow_buf), 0);
fp->_IO_write_base = snf->overflow_buf;
fp->_IO_read_base = snf->overflow_buf;
fp->_IO_read_ptr = snf->overflow_buf;
fp->_IO_read_end = snf->overflow_buf + sizeof (snf->overflow_buf);
}
fp->_IO_write_ptr = snf->overflow_buf;
fp->_IO_write_end = snf->overflow_buf;
/* Since we are not really interested in storing the characters
which do not fit in the buffer we simply ignore it. */
return c;
}
const struct _IO_jump_t _IO_strn_jumps libio_vtable attribute_hidden =
{
JUMP_INIT_DUMMY,
JUMP_INIT(finish, _IO_str_finish),
JUMP_INIT(overflow, _IO_strn_overflow),
JUMP_INIT(underflow, _IO_str_underflow),
JUMP_INIT(uflow, _IO_default_uflow),
JUMP_INIT(pbackfail, _IO_str_pbackfail),
JUMP_INIT(xsputn, _IO_default_xsputn),
JUMP_INIT(xsgetn, _IO_default_xsgetn),
JUMP_INIT(seekoff, _IO_str_seekoff),
JUMP_INIT(seekpos, _IO_default_seekpos),
JUMP_INIT(setbuf, _IO_default_setbuf),
JUMP_INIT(sync, _IO_default_sync),
JUMP_INIT(doallocate, _IO_default_doallocate),
JUMP_INIT(read, _IO_default_read),
JUMP_INIT(write, _IO_default_write),
JUMP_INIT(seek, _IO_default_seek),
JUMP_INIT(close, _IO_default_close),
JUMP_INIT(stat, _IO_default_stat),
JUMP_INIT(showmanyc, _IO_default_showmanyc),
JUMP_INIT(imbue, _IO_default_imbue)
};
int
_IO_vsnprintf (char *string, _IO_size_t maxlen, const char *format,
_IO_va_list args)
{
_IO_strnfile sf;
int ret;
#ifdef _IO_MTSAFE_IO
sf.f._sbf._f._lock = NULL;
#endif
/* We need to handle the special case where MAXLEN is 0. Use the
overflow buffer right from the start. */
if (maxlen == 0)
{
string = sf.overflow_buf;
maxlen = sizeof (sf.overflow_buf);
}
_IO_no_init (&sf.f._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
_IO_JUMPS (&sf.f._sbf) = &_IO_strn_jumps;
string[0] = '\0';
_IO_str_init_static_internal (&sf.f, string, maxlen - 1, string);
ret = _IO_vfprintf (&sf.f._sbf._f, format, args);
if (sf.f._sbf._f._IO_buf_base != sf.overflow_buf)
*sf.f._sbf._f._IO_write_ptr = '\0';
return ret;
}
ldbl_weak_alias (_IO_vsnprintf, __vsnprintf)
ldbl_weak_alias (_IO_vsnprintf, vsnprintf)