sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000-2003,2005,2007
   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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  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 /* Open a directory stream on NAME.  */
  80 DIR *
  81 __opendir (const char *name)
  82 {
  83   struct stat64 statbuf;
  84
  85   if (__builtin_expect (name[0], '\1') == '\0')
  86     {
  87       /* POSIX.1-1990 says an empty name gets ENOENT;
  88          but `open' might like it fine.  */
  89       __set_errno (ENOENT);
  90       return NULL;
  91     }
  92
  93 #ifdef O_DIRECTORY
  94   /* Test whether O_DIRECTORY works.  */
  95   if (o_directory_works == 0)
  96     tryopen_o_directory ();
  97
  98   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  99   if (o_directory_works < 0)
 100 #endif
 101     {
 102       /* We first have to check whether the name is for a directory.  We
 103          cannot do this after the open() call since the open/close operation
 104          performed on, say, a tape device might have undesirable effects.  */
 105       if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
 106         return NULL;
 107       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 108         {
 109           __set_errno (ENOTDIR);
 110           return NULL;
 111          }
 112     }
 113
 114   int flags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE;
 115 #ifdef O_CLOEXEC
 116   flags |= O_CLOEXEC;
 117 #endif
 118   int fd = open_not_cancel_2 (name, flags);
 119   if (__builtin_expect (fd, 0) < 0)
 120     return NULL;
 121
 122   /* Now make sure this really is a directory and nothing changed since
 123      the `stat' call.  We do not have to perform the test for the
 124      descriptor being associated with a directory if we know the
 125      O_DIRECTORY flag is honored by the kernel.  */
 126   if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
 127     goto lose;
 128 #ifdef O_DIRECTORY
 129   if (o_directory_works <= 0)
 130 #endif
 131     {
 132       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 133         {
 134           __set_errno (ENOTDIR);
 135         lose:
 136           close_not_cancel_no_status (fd);
 137           return NULL;
 138         }
 139     }
 140
 141   return __alloc_dir (fd, true, &statbuf);
 142 }
 143 weak_alias (__opendir, opendir)
 144
 145
 146 #ifdef __ASSUME_O_CLOEXEC
 147 # define check_have_o_cloexec(fd) 1
 148 #else
 149 static int
 150 check_have_o_cloexec (int fd)
 151 {
 152   if (__have_o_cloexec == 0)
 153     __have_o_cloexec = (__fcntl (fd, F_GETFD, 0) & FD_CLOEXEC) == 0 ? -1 : 1;
 154   return __have_o_cloexec > 0;
 155 }
 156 #endif
 157
 158
 159 DIR *
 160 internal_function
 161 __alloc_dir (int fd, bool close_fd, const struct stat64 *statp)
 162 {
 163   /* We always have to set the close-on-exit flag if the user provided
 164      the file descriptor.  Otherwise only if we have no working
 165      O_CLOEXEC support.  */
 166 #ifdef O_CLOEXEC
 167   if (! close_fd || ! check_have_o_cloexec (fd))
 168 #endif
 169     {
 170       if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 171         goto lose;
 172     }
 173
 174   const size_t default_allocation = (BUFSIZ < sizeof (struct dirent64)
 175                                      ? sizeof (struct dirent64) : BUFSIZ);
 176   size_t allocation;
 177 #ifdef _STATBUF_ST_BLKSIZE
 178   if (__builtin_expect ((size_t) statp->st_blksize >= sizeof (struct dirent64),
 179                         1))
 180     allocation = statp->st_blksize;
 181   else
 182 #endif
 183     allocation = default_allocation;
 184
 185   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 186   if (dirp == NULL)
 187     {
 188 #ifdef _STATBUF_ST_BLKSIZE
 189       if (allocation == statp->st_blksize
 190           && allocation != default_allocation)
 191         {
 192           allocation = default_allocation;
 193           dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 194         }
 195       if (dirp == NULL)
 196 #endif
 197       lose:
 198         {
 199           if (close_fd)
 200             {
 201               int save_errno = errno;
 202               close_not_cancel_no_status (fd);
 203               __set_errno (save_errno);
 204             }
 205           return NULL;
 206         }
 207     }
 208
 209   dirp->fd = fd;
 210 #ifndef NOT_IN_libc
 211   __libc_lock_init (dirp->lock);
 212 #endif
 213   dirp->allocation = allocation;
 214   dirp->size = 0;
 215   dirp->offset = 0;
 216   dirp->filepos = 0;
 217
 218   return dirp;
 219 }