lib/open.c

   1 /* Open a descriptor to a file.
   2    Copyright (C) 2007-2018 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
  18
  19 /* If the user's config.h happens to include <fcntl.h>, let it include only
  20    the system's <fcntl.h> here, so that orig_open doesn't recurse to
  21    rpl_open.  */
  22 #define __need_system_fcntl_h
  23 #include <config.h>
  24
  25 /* Get the original definition of open.  It might be defined as a macro.  */
  26 #include <fcntl.h>
  27 #include <sys/types.h>
  28 #undef __need_system_fcntl_h
  29
  30 static int
  31 orig_open (const char *filename, int flags, mode_t mode)
  32 {
  33   return open (filename, flags, mode);
  34 }
  35
  36 /* Specification.  */
  37 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
  38    this include because of the preliminary #include <fcntl.h> above.  */
  39 #include "fcntl.h"
  40
  41 #include "cloexec.h"
  42
  43 #include <errno.h>
  44 #include <stdarg.h>
  45 #include <string.h>
  46 #include <sys/types.h>
  47 #include <sys/stat.h>
  48 #include <unistd.h>
  49
  50 #ifndef REPLACE_OPEN_DIRECTORY
  51 # define REPLACE_OPEN_DIRECTORY 0
  52 #endif
  53
  54 int
  55 open (const char *filename, int flags, ...)
  56 {
  57   /* 0 = unknown, 1 = yes, -1 = no.  */
  58 #if GNULIB_defined_O_CLOEXEC
  59   int have_cloexec = -1;
  60 #else
  61   static int have_cloexec;
  62 #endif
  63
  64   mode_t mode;
  65   int fd;
  66
  67   mode = 0;
  68   if (flags & O_CREAT)
  69     {
  70       va_list arg;
  71       va_start (arg, flags);
  72
  73       /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
  74          creates crashing code when 'mode_t' is smaller than 'int'.  */
  75       mode = va_arg (arg, PROMOTED_MODE_T);
  76
  77       va_end (arg);
  78     }
  79
  80 #if GNULIB_defined_O_NONBLOCK
  81   /* The only known platform that lacks O_NONBLOCK is mingw, but it
  82      also lacks named pipes and Unix sockets, which are the only two
  83      file types that require non-blocking handling in open().
  84      Therefore, it is safe to ignore O_NONBLOCK here.  It is handy
  85      that mingw also lacks openat(), so that is also covered here.  */
  86   flags &= ~O_NONBLOCK;
  87 #endif
  88
  89 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  90   if (strcmp (filename, "/dev/null") == 0)
  91     filename = "NUL";
  92 #endif
  93
  94 #if OPEN_TRAILING_SLASH_BUG
  95   /* If the filename ends in a slash and one of O_CREAT, O_WRONLY, O_RDWR
  96      is specified, then fail.
  97      Rationale: POSIX <http://www.opengroup.org/susv3/basedefs/xbd_chap04.html>
  98      says that
  99        "A pathname that contains at least one non-slash character and that
 100         ends with one or more trailing slashes shall be resolved as if a
 101         single dot character ( '.' ) were appended to the pathname."
 102      and
 103        "The special filename dot shall refer to the directory specified by
 104         its predecessor."
 105      If the named file already exists as a directory, then
 106        - if O_CREAT is specified, open() must fail because of the semantics
 107          of O_CREAT,
 108        - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
 109          <http://www.opengroup.org/susv3/functions/open.html> says that it
 110          fails with errno = EISDIR in this case.
 111      If the named file does not exist or does not name a directory, then
 112        - if O_CREAT is specified, open() must fail since open() cannot create
 113          directories,
 114        - if O_WRONLY or O_RDWR is specified, open() must fail because the
 115          file does not contain a '.' directory.  */
 116   if (flags & (O_CREAT | O_WRONLY | O_RDWR))
 117     {
 118       size_t len = strlen (filename);
 119       if (len > 0 && filename[len - 1] == '/')
 120         {
 121           errno = EISDIR;
 122           return -1;
 123         }
 124     }
 125 #endif
 126
 127   fd = orig_open (filename,
 128                   flags & ~(have_cloexec <= 0 ? O_CLOEXEC : 0), mode);
 129
 130   if (flags & O_CLOEXEC)
 131     {
 132       if (! have_cloexec)
 133         {
 134           if (0 <= fd)
 135             have_cloexec = 1;
 136           else if (errno == EINVAL)
 137             {
 138               fd = orig_open (filename, flags & ~O_CLOEXEC, mode);
 139               have_cloexec = -1;
 140             }
 141         }
 142       if (have_cloexec < 0 && 0 <= fd)
 143         set_cloexec_flag (fd, true);
 144     }
 145
 146
 147 #if REPLACE_FCHDIR
 148   /* Implementing fchdir and fdopendir requires the ability to open a
 149      directory file descriptor.  If open doesn't support that (as on
 150      mingw), we use a dummy file that behaves the same as directories
 151      on Linux (ie. always reports EOF on attempts to read()), and
 152      override fstat() in fchdir.c to hide the fact that we have a
 153      dummy.  */
 154   if (REPLACE_OPEN_DIRECTORY && fd < 0 && errno == EACCES
 155       && ((flags & O_ACCMODE) == O_RDONLY
 156           || (O_SEARCH != O_RDONLY && (flags & O_ACCMODE) == O_SEARCH)))
 157     {
 158       struct stat statbuf;
 159       if (stat (filename, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))
 160         {
 161           /* Maximum recursion depth of 1.  */
 162           fd = open ("/dev/null", flags, mode);
 163           if (0 <= fd)
 164             fd = _gl_register_fd (fd, filename);
 165         }
 166       else
 167         errno = EACCES;
 168     }
 169 #endif
 170
 171 #if OPEN_TRAILING_SLASH_BUG
 172   /* If the filename ends in a slash and fd does not refer to a directory,
 173      then fail.
 174      Rationale: POSIX <http://www.opengroup.org/susv3/basedefs/xbd_chap04.html>
 175      says that
 176        "A pathname that contains at least one non-slash character and that
 177         ends with one or more trailing slashes shall be resolved as if a
 178         single dot character ( '.' ) were appended to the pathname."
 179      and
 180        "The special filename dot shall refer to the directory specified by
 181         its predecessor."
 182      If the named file without the slash is not a directory, open() must fail
 183      with ENOTDIR.  */
 184   if (fd >= 0)
 185     {
 186       /* We know len is positive, since open did not fail with ENOENT.  */
 187       size_t len = strlen (filename);
 188       if (filename[len - 1] == '/')
 189         {
 190           struct stat statbuf;
 191
 192           if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
 193             {
 194               close (fd);
 195               errno = ENOTDIR;
 196               return -1;
 197             }
 198         }
 199     }
 200 #endif
 201
 202 #if REPLACE_FCHDIR
 203   if (!REPLACE_OPEN_DIRECTORY && 0 <= fd)
 204     fd = _gl_register_fd (fd, filename);
 205 #endif
 206
 207   return fd;
 208 }