glibc/debug/vdprintf_chk.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

68 lines
2.3 KiB
C

/* Copyright (C) 1995-2016 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 <stdio_ext.h>
int
__vdprintf_chk (int d, int flags, const char *format, va_list arg)
{
struct _IO_FILE_plus tmpfil;
struct _IO_wide_data wd;
int done;
#ifdef _IO_MTSAFE_IO
tmpfil.file._lock = NULL;
#endif
_IO_no_init (&tmpfil.file, _IO_USER_LOCK, 0, &wd, &_IO_wfile_jumps);
_IO_JUMPS (&tmpfil) = &_IO_file_jumps;
_IO_new_file_init_internal (&tmpfil);
#if !_IO_UNIFIED_JUMPTABLES
tmpfil.vtable = NULL;
#endif
if (_IO_file_attach (&tmpfil.file, d) == NULL)
{
_IO_un_link (&tmpfil);
return EOF;
}
tmpfil.file._flags |= _IO_DELETE_DONT_CLOSE;
_IO_mask_flags (&tmpfil.file, _IO_NO_READS,
_IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING);
/* For flags > 0 (i.e. __USE_FORTIFY_LEVEL > 1) request that %n
can only come from read-only format strings. */
if (flags > 0)
tmpfil.file._flags2 |= _IO_FLAGS2_FORTIFY;
done = _IO_vfprintf (&tmpfil.file, format, arg);
_IO_FINISH (&tmpfil.file);
return done;
}
libc_hidden_def (__vdprintf_chk)