libio/vtables.c

   1 /* libio vtable validation.
   2    Copyright (C) 2016-2023 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 #include <pointer_guard.h>
  24
  25 #ifdef SHARED
  26
  27 void (*IO_accept_foreign_vtables) (void) attribute_hidden;
  28
  29 #else  /* !SHARED */
  30
  31 /* Used to check whether static dlopen support is needed.  */
  32 # pragma weak __dlopen
  33
  34 #endif
  35
  36 void attribute_hidden
  37 _IO_vtable_check (void)
  38 {
  39 #ifdef SHARED
  40   /* Honor the compatibility flag.  */
  41   void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
  42   PTR_DEMANGLE (flag);
  43   if (flag == &_IO_vtable_check)
  44     return;
  45
  46   /* In case this libc copy is in a non-default namespace, we always
  47      need to accept foreign vtables because there is always a
  48      possibility that FILE * objects are passed across the linking
  49      boundary.  */
  50   {
  51     Dl_info di;
  52     struct link_map *l;
  53     if (!rtld_active ()
  54         || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
  55             && l->l_ns != LM_ID_BASE))
  56       return;
  57   }
  58
  59 #else /* !SHARED */
  60   /* We cannot perform vtable validation in the static dlopen case
  61      because FILE * handles might be passed back and forth across the
  62      boundary.  Therefore, we disable checking in this case.  */
  63   if (__dlopen != NULL)
  64     return;
  65 #endif
  66
  67   __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
  68 }
  69
  70 /* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
  71    install their own vtables directly, without calling _IO_init or
  72    other functions.  Detect this by looking at the vtables values
  73    during startup, and disable vtable validation in this case.  */
  74 #ifdef SHARED
  75 __attribute__ ((constructor))
  76 static void
  77 check_stdfiles_vtables (void)
  78 {
  79   if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
  80       || _IO_2_1_stdout_.vtable != &_IO_file_jumps
  81       || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
  82     IO_set_accept_foreign_vtables (&_IO_vtable_check);
  83 }
  84 #endif