sysdeps/mach/hurd/check_fds.c

   1 /* Copyright (C) 2000 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <fcntl.h>
  20 #include <paths.h>
  21 #include <unistd.h>
  22
  23 #include <hurd.h>
  24 #include <hurd/fd.h>
  25
  26 #include <set-hooks.h>
  27
  28 /* Try to get a machine dependent instruction which will make the
  29    program crash.  This is used in case everything else fails.  */
  30 #include <abort-instr.h>
  31 #ifndef ABORT_INSTRUCTION
  32 /* No such instruction is available.  */
  33 # define ABORT_INSTRUCTION
  34 #endif
  35
  36 static void
  37 check_one_fd (int fd, int mode)
  38 {
  39   struct hurd_fd *d;
  40
  41   d = _hurd_fd_get (fd);
  42   if (d == NULL)
  43     {
  44       /* This descriptor hasn't been opened.  We try to allocate the
  45          descriptor and open /dev/null on it so that the SUID program
  46          we are about to start does not accidently use this
  47          descriptor.  */
  48       d = _hurd_alloc_fd (NULL, fd);
  49       if (d != NULL)
  50         {
  51           mach_port_t port;
  52
  53           port = __file_name_lookup (_PATH_DEVNULL, mode, 0);
  54           if (port)
  55             {
  56               /* Since /dev/null isn't supposed to be a terminal, we
  57                  avoid any ctty magic.  */
  58               d->port.port = port;
  59               d->flags = 0;
  60
  61               __spin_unlock (&d->port.lock);
  62               return;
  63             }
  64         }
  65
  66       /* We cannot even give an error message here since it would run
  67          into the same problems.  */
  68       while (1)
  69         /* Try for ever and ever.  */
  70         ABORT_INSTRUCTION;
  71     }
  72 }
  73
  74 static void
  75 check_standard_fds (void)
  76 {
  77   /* Check all three standard file descriptors.  */
  78   check_one_fd (STDIN_FILENO, O_RDONLY);
  79   check_one_fd (STDOUT_FILENO, O_RDWR);
  80   check_one_fd (STDERR_FILENO, O_RDWR);
  81 }
  82
  83 static void
  84 init_standard_fds (void)
  85 {
  86   /* Now that we have FDs, make sure that, if this is a SUID program,
  87      FDs 0, 1 and 2 are allocated.  If necessary we'll set them up
  88      ourselves.  If that's not possible we stop the program.  */
  89   if (__builtin_expect (__libc_enable_secure, 0))
  90     check_standard_fds ();
  91
  92   (void) &init_standard_fds;    /* Avoid "defined but not used" warning.  */
  93 }
  94 text_set_element (_hurd_fd_subinit, init_standard_fds);
  95 \f
  96
  97 #ifndef SHARED
  98 void
  99 __libc_check_standard_fds (void)
 100 {
 101   /* We don't check the standard file descriptors here.  They will be
 102      checked when we initialize the file descriptor table, as part of
 103      the _hurd_fd_subinit hook.
 104
 105      This function is only present to make sure that this module gets
 106      linked in when part of the static libc.  */
 107 }
 108 #endif