sysdeps/mach/hurd/check_fds.c

   1 /* Copyright (C) 2000-2019 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <fcntl.h>
  19 #include <paths.h>
  20 #include <unistd.h>
  21
  22 #include <hurd.h>
  23 #include <hurd/fd.h>
  24
  25 #include <set-hooks.h>
  26
  27 /* Try to get a machine dependent instruction which will make the
  28    program crash.  This is used in case everything else fails.  */
  29 #include <abort-instr.h>
  30 #ifndef ABORT_INSTRUCTION
  31 /* No such instruction is available.  */
  32 # define ABORT_INSTRUCTION
  33 #endif
  34
  35 static void
  36 check_one_fd (int fd, int mode)
  37 {
  38   struct hurd_fd *d;
  39
  40   d = _hurd_fd_get (fd);
  41   if (d == NULL)
  42     {
  43       /* This descriptor hasn't been opened.  We try to allocate the
  44          descriptor and open /dev/null on it so that the SUID program
  45          we are about to start does not accidentally use this
  46          descriptor.  */
  47       d = _hurd_alloc_fd (NULL, fd);
  48       if (d != NULL)
  49         {
  50           mach_port_t port;
  51
  52           port = __file_name_lookup (_PATH_DEVNULL, mode, 0);
  53           if (port)
  54             {
  55               /* Since /dev/null isn't supposed to be a terminal, we
  56                  avoid any ctty magic.  */
  57               d->port.port = port;
  58               d->flags = 0;
  59
  60               __spin_unlock (&d->port.lock);
  61               return;
  62             }
  63         }
  64
  65       /* We cannot even give an error message here since it would run
  66          into the same problems.  */
  67       while (1)
  68         /* Try for ever and ever.  */
  69         ABORT_INSTRUCTION;
  70     }
  71 }
  72
  73 static void
  74 check_standard_fds (void)
  75 {
  76   /* Check all three standard file descriptors.  */
  77   check_one_fd (STDIN_FILENO, O_RDONLY);
  78   check_one_fd (STDOUT_FILENO, O_RDWR);
  79   check_one_fd (STDERR_FILENO, O_RDWR);
  80 }
  81
  82 static void
  83 init_standard_fds (void)
  84 {
  85   /* Now that we have FDs, make sure that, if this is a SUID program,
  86      FDs 0, 1 and 2 are allocated.  If necessary we'll set them up
  87      ourselves.  If that's not possible we stop the program.  */
  88   if (__builtin_expect (__libc_enable_secure, 0))
  89     check_standard_fds ();
  90
  91   (void) &init_standard_fds;    /* Avoid "defined but not used" warning.  */
  92 }
  93 text_set_element (_hurd_fd_subinit, init_standard_fds);
  94 \f
  95
  96 #ifndef SHARED
  97 void
  98 __libc_check_standard_fds (void)
  99 {
 100   /* We don't check the standard file descriptors here.  They will be
 101      checked when we initialize the file descriptor table, as part of
 102      the _hurd_fd_subinit hook.
 103
 104      This function is only present to make sure that this module gets
 105      linked in when part of the static libc.  */
 106 }
 107 #endif