libio/vtables.c

   1 /* libio vtable validation.
   2    Copyright (C) 2016-2022 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <dlfcn.h>
  20 #include <libioP.h>
  21 #include <stdio.h>
  22 #include <ldsodefs.h>
  23
  24 #ifdef SHARED
  25
  26 void (*IO_accept_foreign_vtables) (void) attribute_hidden;
  27
  28 #else  /* !SHARED */
  29
  30 /* Used to check whether static dlopen support is needed.  */
  31 # pragma weak __dlopen
  32
  33 #endif
  34
  35 void attribute_hidden
  36 _IO_vtable_check (void)
  37 {
  38 #ifdef SHARED
  39   /* Honor the compatibility flag.  */
  40   void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
  41 #ifdef PTR_DEMANGLE
  42   PTR_DEMANGLE (flag);
  43 #endif
  44   if (flag == &_IO_vtable_check)
  45     return;
  46
  47   /* In case this libc copy is in a non-default namespace, we always
  48      need to accept foreign vtables because there is always a
  49      possibility that FILE * objects are passed across the linking
  50      boundary.  */
  51   {
  52     Dl_info di;
  53     struct link_map *l;
  54     if (!rtld_active ()
  55         || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
  56             && l->l_ns != LM_ID_BASE))
  57       return;
  58   }
  59
  60 #else /* !SHARED */
  61   /* We cannot perform vtable validation in the static dlopen case
  62      because FILE * handles might be passed back and forth across the
  63      boundary.  Therefore, we disable checking in this case.  */
  64   if (__dlopen != NULL)
  65     return;
  66 #endif
  67
  68   __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
  69 }
  70
  71 /* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
  72    install their own vtables directly, without calling _IO_init or
  73    other functions.  Detect this by looking at the vtables values
  74    during startup, and disable vtable validation in this case.  */
  75 #ifdef SHARED
  76 __attribute__ ((constructor))
  77 static void
  78 check_stdfiles_vtables (void)
  79 {
  80   if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
  81       || _IO_2_1_stdout_.vtable != &_IO_file_jumps
  82       || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
  83     IO_set_accept_foreign_vtables (&_IO_vtable_check);
  84 }
  85 #endif