gl/open.c

   1 /* Open a descriptor to a file.
   2    Copyright (C) 2007-2023 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser 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 #if defined _WIN32 && !defined __CYGWIN__
  34   return _open (filename, flags, mode);
  35 #else
  36   return open (filename, flags, mode);
  37 #endif
  38 }
  39
  40 /* Specification.  */
  41 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
  42    this include because of the preliminary #include <fcntl.h> above.  */
  43 #include "fcntl.h"
  44
  45 #include "cloexec.h"
  46
  47 #include <errno.h>
  48 #include <stdarg.h>
  49 #include <string.h>
  50 #include <sys/types.h>
  51 #include <sys/stat.h>
  52 #include <unistd.h>
  53
  54 #ifndef REPLACE_OPEN_DIRECTORY
  55 # define REPLACE_OPEN_DIRECTORY 0
  56 #endif
  57
  58 int
  59 open (const char *filename, int flags, ...)
  60 {
  61   /* 0 = unknown, 1 = yes, -1 = no.  */
  62 #if GNULIB_defined_O_CLOEXEC
  63   int have_cloexec = -1;
  64 #else
  65   static int have_cloexec;
  66 #endif
  67
  68   mode_t mode;
  69   int fd;
  70
  71   mode = 0;
  72   if (flags & O_CREAT)
  73     {
  74       va_list arg;
  75       va_start (arg, flags);
  76
  77       /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
  78          creates crashing code when 'mode_t' is smaller than 'int'.  */
  79       mode = va_arg (arg, PROMOTED_MODE_T);
  80
  81       va_end (arg);
  82     }
  83
  84 #if GNULIB_defined_O_NONBLOCK
  85   /* The only known platform that lacks O_NONBLOCK is mingw, but it
  86      also lacks named pipes and Unix sockets, which are the only two
  87      file types that require non-blocking handling in open().
  88      Therefore, it is safe to ignore O_NONBLOCK here.  It is handy
  89      that mingw also lacks openat(), so that is also covered here.  */
  90   flags &= ~O_NONBLOCK;
  91 #endif
  92
  93 #if defined _WIN32 && ! defined __CYGWIN__
  94   if (strcmp (filename, "/dev/null") == 0)
  95     filename = "NUL";
  96 #endif
  97
  98 #if OPEN_TRAILING_SLASH_BUG
  99   /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
 100      ends in a slash, as POSIX says such a filename must name a directory
 101      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
 102        "A pathname that contains at least one non-<slash> character and that
 103         ends with one or more trailing <slash> characters shall not be resolved
 104         successfully unless the last pathname component before the trailing
 105         <slash> characters names an existing directory"
 106      If the named file already exists as a directory, then
 107        - if O_CREAT is specified, open() must fail because of the semantics
 108          of O_CREAT,
 109        - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
 110          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html>
 111          says that it fails with errno = EISDIR in this case.
 112      If the named file does not exist or does not name a directory, then
 113        - if O_CREAT is specified, open() must fail since open() cannot create
 114          directories,
 115        - if O_WRONLY or O_RDWR is specified, open() must fail because the
 116          file does not contain a '.' directory.  */
 117   if ((flags & O_CREAT)
 118       || (flags & O_ACCMODE) == O_RDWR
 119       || (flags & O_ACCMODE) == O_WRONLY)
 120     {
 121       size_t len = strlen (filename);
 122       if (len > 0 && filename[len - 1] == '/')
 123         {
 124           errno = EISDIR;
 125           return -1;
 126         }
 127     }
 128 #endif
 129
 130   fd = orig_open (filename,
 131                   flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
 132
 133   if (flags & O_CLOEXEC)
 134     {
 135       if (! have_cloexec)
 136         {
 137           if (0 <= fd)
 138             have_cloexec = 1;
 139           else if (errno == EINVAL)
 140             {
 141               fd = orig_open (filename, flags & ~O_CLOEXEC, mode);
 142               have_cloexec = -1;
 143             }
 144         }
 145       if (have_cloexec < 0 && 0 <= fd)
 146         set_cloexec_flag (fd, true);
 147     }
 148
 149
 150 #if REPLACE_FCHDIR
 151   /* Implementing fchdir and fdopendir requires the ability to open a
 152      directory file descriptor.  If open doesn't support that (as on
 153      mingw), we use a dummy file that behaves the same as directories
 154      on Linux (ie. always reports EOF on attempts to read()), and
 155      override fstat() in fchdir.c to hide the fact that we have a
 156      dummy.  */
 157   if (REPLACE_OPEN_DIRECTORY && fd < 0 && errno == EACCES
 158       && ((flags & O_ACCMODE) == O_RDONLY
 159           || (O_SEARCH != O_RDONLY && (flags & O_ACCMODE) == O_SEARCH)))
 160     {
 161       struct stat statbuf;
 162       if (stat (filename, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))
 163         {
 164           /* Maximum recursion depth of 1.  */
 165           fd = open ("/dev/null", flags, mode);
 166           if (0 <= fd)
 167             fd = _gl_register_fd (fd, filename);
 168         }
 169       else
 170         errno = EACCES;
 171     }
 172 #endif
 173
 174 #if OPEN_TRAILING_SLASH_BUG
 175   /* If the filename ends in a slash and fd does not refer to a directory,
 176      then fail.
 177      Rationale: POSIX says such a filename must name a directory
 178      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
 179        "A pathname that contains at least one non-<slash> character and that
 180         ends with one or more trailing <slash> characters shall not be resolved
 181         successfully unless the last pathname component before the trailing
 182         <slash> characters names an existing directory"
 183      If the named file without the slash is not a directory, open() must fail
 184      with ENOTDIR.  */
 185   if (fd >= 0)
 186     {
 187       /* We know len is positive, since open did not fail with ENOENT.  */
 188       size_t len = strlen (filename);
 189       if (filename[len - 1] == '/')
 190         {
 191           struct stat statbuf;
 192
 193           if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
 194             {
 195               close (fd);
 196               errno = ENOTDIR;
 197               return -1;
 198             }
 199         }
 200     }
 201 #endif
 202
 203 #if REPLACE_FCHDIR
 204   if (!REPLACE_OPEN_DIRECTORY && 0 <= fd)
 205     fd = _gl_register_fd (fd, filename);
 206 #endif
 207
 208   return fd;
 209 }