sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000-2003,2005,2007,2009,2011
   2    Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <dirent.h>
  25 #include <fcntl.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include <stdio.h>
  30 #include <string.h>
  31
  32 #include <dirstream.h>
  33 #include <not-cancel.h>
  34 #include <kernel-features.h>
  35
  36
  37 /* opendir() must not accidentally open something other than a directory.
  38    Some OS's have kernel support for that, some don't.  In the worst
  39    case we have to stat() before the open() AND fstat() after.
  40
  41    We have to test at runtime for kernel support since libc may have
  42    been compiled with different headers to the kernel it's running on.
  43    This test can't be done reliably in the general case.  We'll use
  44    /dev/null, which if it's not a device lots of stuff will break, as
  45    a guinea pig.  It may be missing in chroot environments, so we
  46    make sure to fail safe. */
  47 #ifdef O_DIRECTORY
  48 # ifdef O_DIRECTORY_WORKS
  49 #  define o_directory_works 1
  50 #  define tryopen_o_directory() while (1) /* This must not be called.  */
  51 # else
  52 static int o_directory_works;
  53
  54 static void
  55 tryopen_o_directory (void)
  56 {
  57   int serrno = errno;
  58   int x = open_not_cancel_2 ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  59
  60   if (x >= 0)
  61     {
  62       close_not_cancel_no_status (x);
  63       o_directory_works = -1;
  64     }
  65   else if (errno != ENOTDIR)
  66     o_directory_works = -1;
  67   else
  68     o_directory_works = 1;
  69
  70   __set_errno (serrno);
  71 }
  72 # endif
  73 # define EXTRA_FLAGS O_DIRECTORY
  74 #else
  75 # define EXTRA_FLAGS 0
  76 #endif
  77
  78
  79 DIR *
  80 internal_function
  81 __opendirat (int dfd, const char *name)
  82 {
  83   struct stat64 statbuf;
  84   struct stat64 *statp = NULL;
  85
  86   if (__builtin_expect (name[0], '\1') == '\0')
  87     {
  88       /* POSIX.1-1990 says an empty name gets ENOENT;
  89          but `open' might like it fine.  */
  90       __set_errno (ENOENT);
  91       return NULL;
  92     }
  93
  94 #ifdef O_DIRECTORY
  95   /* Test whether O_DIRECTORY works.  */
  96   if (o_directory_works == 0)
  97     tryopen_o_directory ();
  98
  99   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
 100   if (o_directory_works < 0)
 101 #endif
 102     {
 103       /* We first have to check whether the name is for a directory.  We
 104          cannot do this after the open() call since the open/close operation
 105          performed on, say, a tape device might have undesirable effects.  */
 106       if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
 107         return NULL;
 108       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 109         {
 110           __set_errno (ENOTDIR);
 111           return NULL;
 112          }
 113     }
 114
 115   int flags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE;
 116 #ifdef O_CLOEXEC
 117   flags |= O_CLOEXEC;
 118 #endif
 119   int fd;
 120 #ifdef IS_IN_rtld
 121   assert (dfd == AT_FDCWD);
 122   fd = open_not_cancel_2 (name, flags);
 123 #else
 124   fd = openat_not_cancel_3 (dfd, name, flags);
 125 #endif
 126   if (__builtin_expect (fd, 0) < 0)
 127     return NULL;
 128
 129 #ifdef O_DIRECTORY
 130   if (o_directory_works <= 0)
 131 #endif
 132     {
 133       /* Now make sure this really is a directory and nothing changed since
 134          the `stat' call.  */
 135       if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
 136         goto lose;
 137       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 138         {
 139           __set_errno (ENOTDIR);
 140         lose:
 141           close_not_cancel_no_status (fd);
 142           return NULL;
 143         }
 144       statp = &statbuf;
 145     }
 146
 147   return __alloc_dir (fd, true, 0, statp);
 148 }
 149
 150
 151 /* Open a directory stream on NAME.  */
 152 DIR *
 153 __opendir (const char *name)
 154 {
 155   return __opendirat (AT_FDCWD, name);
 156 }
 157 weak_alias (__opendir, opendir)
 158
 159
 160 #ifdef __ASSUME_O_CLOEXEC
 161 # define check_have_o_cloexec(fd) 1
 162 #else
 163 static int
 164 check_have_o_cloexec (int fd)
 165 {
 166   if (__have_o_cloexec == 0)
 167     __have_o_cloexec = (__fcntl (fd, F_GETFD, 0) & FD_CLOEXEC) == 0 ? -1 : 1;
 168   return __have_o_cloexec > 0;
 169 }
 170 #endif
 171
 172
 173 DIR *
 174 internal_function
 175 __alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
 176 {
 177   /* We always have to set the close-on-exit flag if the user provided
 178      the file descriptor.  Otherwise only if we have no working
 179      O_CLOEXEC support.  */
 180 #ifdef O_CLOEXEC
 181   if ((! close_fd && (flags & O_CLOEXEC) == 0)
 182       || ! check_have_o_cloexec (fd))
 183 #endif
 184     {
 185       if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 186         goto lose;
 187     }
 188
 189   const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
 190                                      ? sizeof (struct dirent64) : 4 * BUFSIZ);
 191   const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
 192                                    ? sizeof (struct dirent64) : BUFSIZ);
 193   size_t allocation = default_allocation;
 194 #ifdef _STATBUF_ST_BLKSIZE
 195   if (statp != NULL && default_allocation < statp->st_blksize)
 196     allocation = statp->st_blksize;
 197 #endif
 198
 199   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 200   if (dirp == NULL)
 201     {
 202       allocation = small_allocation;
 203       dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 204
 205       if (dirp == NULL)
 206       lose:
 207         {
 208           if (close_fd)
 209             {
 210               int save_errno = errno;
 211               close_not_cancel_no_status (fd);
 212               __set_errno (save_errno);
 213             }
 214           return NULL;
 215         }
 216     }
 217
 218   dirp->fd = fd;
 219 #ifndef NOT_IN_libc
 220   __libc_lock_init (dirp->lock);
 221 #endif
 222   dirp->allocation = allocation;
 223   dirp->size = 0;
 224   dirp->offset = 0;
 225   dirp->filepos = 0;
 226
 227   return dirp;
 228 }