lib/open.c

   1 /* Open a descriptor to a file.
   2    Copyright (C) 2007-2024 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 #ifdef __osf__
  42 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
  43    this include because of the preliminary #include <fcntl.h> above.  */
  44 # include "fcntl.h"
  45 #else
  46 # include <fcntl.h>
  47 #endif
  48
  49 #include "cloexec.h"
  50
  51 #include <errno.h>
  52 #include <stdarg.h>
  53 #include <string.h>
  54 #include <sys/types.h>
  55 #include <sys/stat.h>
  56 #include <unistd.h>
  57
  58 #ifndef REPLACE_OPEN_DIRECTORY
  59 # define REPLACE_OPEN_DIRECTORY 0
  60 #endif
  61
  62 int
  63 open (const char *filename, int flags, ...)
  64 {
  65   /* 0 = unknown, 1 = yes, -1 = no.  */
  66 #if GNULIB_defined_O_CLOEXEC
  67   int have_cloexec = -1;
  68 #else
  69   static int have_cloexec;
  70 #endif
  71
  72   mode_t mode;
  73   int fd;
  74
  75   mode = 0;
  76   if (flags & O_CREAT)
  77     {
  78       va_list arg;
  79       va_start (arg, flags);
  80
  81       /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
  82          creates crashing code when 'mode_t' is smaller than 'int'.  */
  83       mode = va_arg (arg, PROMOTED_MODE_T);
  84
  85       va_end (arg);
  86     }
  87
  88 #if GNULIB_defined_O_NONBLOCK
  89   /* The only known platform that lacks O_NONBLOCK is mingw, but it
  90      also lacks named pipes and Unix sockets, which are the only two
  91      file types that require non-blocking handling in open().
  92      Therefore, it is safe to ignore O_NONBLOCK here.  It is handy
  93      that mingw also lacks openat(), so that is also covered here.  */
  94   flags &= ~O_NONBLOCK;
  95 #endif
  96
  97 #if defined _WIN32 && ! defined __CYGWIN__
  98   if (strcmp (filename, "/dev/null") == 0)
  99     filename = "NUL";
 100 #endif
 101
 102 #if OPEN_TRAILING_SLASH_BUG
 103   /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
 104      ends in a slash, as POSIX says such a filename must name a directory
 105      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
 106        "A pathname that contains at least one non-<slash> character and that
 107         ends with one or more trailing <slash> characters shall not be resolved
 108         successfully unless the last pathname component before the trailing
 109         <slash> characters names an existing directory"
 110      If the named file already exists as a directory, then
 111        - if O_CREAT is specified, open() must fail because of the semantics
 112          of O_CREAT,
 113        - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
 114          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html>
 115          says that it fails with errno = EISDIR in this case.
 116      If the named file does not exist or does not name a directory, then
 117        - if O_CREAT is specified, open() must fail since open() cannot create
 118          directories,
 119        - if O_WRONLY or O_RDWR is specified, open() must fail because the
 120          file does not contain a '.' directory.  */
 121   if ((flags & O_CREAT)
 122       || (flags & O_ACCMODE) == O_RDWR
 123       || (flags & O_ACCMODE) == O_WRONLY)
 124     {
 125       size_t len = strlen (filename);
 126       if (len > 0 && filename[len - 1] == '/')
 127         {
 128           errno = EISDIR;
 129           return -1;
 130         }
 131     }
 132 #endif
 133
 134   fd = orig_open (filename,
 135                   flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
 136
 137   if (flags & O_CLOEXEC)
 138     {
 139       if (! have_cloexec)
 140         {
 141           if (0 <= fd)
 142             have_cloexec = 1;
 143           else if (errno == EINVAL)
 144             {
 145               fd = orig_open (filename, flags & ~O_CLOEXEC, mode);
 146               have_cloexec = -1;
 147             }
 148         }
 149       if (have_cloexec < 0 && 0 <= fd)
 150         set_cloexec_flag (fd, true);
 151     }
 152
 153
 154 #if REPLACE_FCHDIR
 155   /* Implementing fchdir and fdopendir requires the ability to open a
 156      directory file descriptor.  If open doesn't support that (as on
 157      mingw), we use a dummy file that behaves the same as directories
 158      on Linux (ie. always reports EOF on attempts to read()), and
 159      override fstat() in fchdir.c to hide the fact that we have a
 160      dummy.  */
 161   if (REPLACE_OPEN_DIRECTORY && fd < 0 && errno == EACCES
 162       && ((flags & O_ACCMODE) == O_RDONLY
 163           || (O_SEARCH != O_RDONLY && (flags & O_ACCMODE) == O_SEARCH)))
 164     {
 165       struct stat statbuf;
 166       if (stat (filename, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))
 167         {
 168           /* Maximum recursion depth of 1.  */
 169           fd = open ("/dev/null", flags, mode);
 170           if (0 <= fd)
 171             fd = _gl_register_fd (fd, filename);
 172         }
 173       else
 174         errno = EACCES;
 175     }
 176 #endif
 177
 178 #if OPEN_TRAILING_SLASH_BUG
 179   /* If the filename ends in a slash and fd does not refer to a directory,
 180      then fail.
 181      Rationale: POSIX says such a filename must name a directory
 182      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
 183        "A pathname that contains at least one non-<slash> character and that
 184         ends with one or more trailing <slash> characters shall not be resolved
 185         successfully unless the last pathname component before the trailing
 186         <slash> characters names an existing directory"
 187      If the named file without the slash is not a directory, open() must fail
 188      with ENOTDIR.  */
 189   if (fd >= 0)
 190     {
 191       /* We know len is positive, since open did not fail with ENOENT.  */
 192       size_t len = strlen (filename);
 193       if (filename[len - 1] == '/')
 194         {
 195           struct stat statbuf;
 196
 197           if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
 198             {
 199               close (fd);
 200               errno = ENOTDIR;
 201               return -1;
 202             }
 203         }
 204     }
 205 #endif
 206
 207 #if REPLACE_FCHDIR
 208   if (!REPLACE_OPEN_DIRECTORY && 0 <= fd)
 209     fd = _gl_register_fd (fd, filename);
 210 #endif
 211
 212   return fd;
 213 }