libio/vtables.c

   1 /* libio vtable validation.
   2    Copyright (C) 2016-2021 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 /* Used to detected multiple libcs.  */
  29 extern struct dl_open_hook *_dl_open_hook;
  30 libc_hidden_proto (_dl_open_hook);
  31
  32 #else  /* !SHARED */
  33
  34 /* Used to check whether static dlopen support is needed.  */
  35 # pragma weak __dlopen
  36
  37 #endif
  38
  39 void attribute_hidden
  40 _IO_vtable_check (void)
  41 {
  42 #ifdef SHARED
  43   /* Honor the compatibility flag.  */
  44   void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
  45 #ifdef PTR_DEMANGLE
  46   PTR_DEMANGLE (flag);
  47 #endif
  48   if (flag == &_IO_vtable_check)
  49     return;
  50
  51   /* In case this libc copy is in a non-default namespace, we always
  52      need to accept foreign vtables because there is always a
  53      possibility that FILE * objects are passed across the linking
  54      boundary.  */
  55   {
  56     Dl_info di;
  57     struct link_map *l;
  58     if (!rtld_active ()
  59         || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
  60             && l->l_ns != LM_ID_BASE))
  61       return;
  62   }
  63
  64 #else /* !SHARED */
  65   /* We cannot perform vtable validation in the static dlopen case
  66      because FILE * handles might be passed back and forth across the
  67      boundary.  Therefore, we disable checking in this case.  */
  68   if (__dlopen != NULL)
  69     return;
  70 #endif
  71
  72   __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
  73 }
  74
  75 /* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
  76    install their own vtables directly, without calling _IO_init or
  77    other functions.  Detect this by looking at the vtables values
  78    during startup, and disable vtable validation in this case.  */
  79 #ifdef SHARED
  80 __attribute__ ((constructor))
  81 static void
  82 check_stdfiles_vtables (void)
  83 {
  84   if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
  85       || _IO_2_1_stdout_.vtable != &_IO_file_jumps
  86       || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
  87     IO_set_accept_foreign_vtables (&_IO_vtable_check);
  88 }
  89 #endif