about summary refs log tree commit diff
path: root/sysdeps/posix/opendir.c
blob: d925804e8990f74782c780ebacf0e361621d1325 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

#include <dirstream.h>
#include <not-cancel.h>
#include <kernel-features.h>

/* The st_blksize value of the directory is used as a hint for the
   size of the buffer which receives struct dirent values from the
   kernel.  st_blksize is limited to MAX_DIR_BUFFER_SIZE, in case the
   file system provides a bogus value.  */
#define MAX_DIR_BUFFER_SIZE 1048576U

/* opendir() must not accidentally open something other than a directory.
   Some OS's have kernel support for that, some don't.  In the worst
   case we have to stat() before the open() AND fstat() after.

   We have to test at runtime for kernel support since libc may have
   been compiled with different headers to the kernel it's running on.
   This test can't be done reliably in the general case.  We'll use
   /dev/null, which if it's not a device lots of stuff will break, as
   a guinea pig.  It may be missing in chroot environments, so we
   make sure to fail safe. */
#ifdef O_DIRECTORY
# ifdef O_DIRECTORY_WORKS
#  define o_directory_works 1
#  define tryopen_o_directory() while (1) /* This must not be called.  */
# else
static int o_directory_works;

static void
tryopen_o_directory (void)
{
  int serrno = errno;
  int x = __open_nocancel ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);

  if (x >= 0)
    {
      __close_nocancel_nostatus (x);
      o_directory_works = -1;
    }
  else if (errno != ENOTDIR)
    o_directory_works = -1;
  else
    o_directory_works = 1;

  __set_errno (serrno);
}
# endif
# define EXTRA_FLAGS O_DIRECTORY
#else
# define EXTRA_FLAGS 0
#endif

enum {
  opendir_oflags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE|O_CLOEXEC
};

static bool
invalid_name (const char *name)
{
  if (__glibc_unlikely (name[0] == '\0'))
    {
      /* POSIX.1-1990 says an empty name gets ENOENT;
	 but `open' might like it fine.  */
      __set_errno (ENOENT);
      return true;
    }
  return false;
}


static bool
need_isdir_precheck (void)
{
#ifdef O_DIRECTORY
  /* Test whether O_DIRECTORY works.  */
  if (o_directory_works == 0)
    tryopen_o_directory ();

  /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  return o_directory_works < 0;
#endif
  return true;
}

static DIR *
opendir_tail (int fd)
{
  if (__glibc_unlikely (fd < 0))
    return NULL;

  /* Now make sure this really is a directory and nothing changed since the
     `stat' call.  The S_ISDIR check is superfluous if O_DIRECTORY works,
     but it's cheap and we need the stat call for st_blksize anyway.  */
  struct stat64 statbuf;
  if (__glibc_unlikely (__fxstat64 (_STAT_VER, fd, &statbuf) < 0))
    goto lose;
  if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
    {
      __set_errno (ENOTDIR);
    lose:
      __close_nocancel_nostatus (fd);
      return NULL;
    }

  return __alloc_dir (fd, true, 0, &statbuf);
}


#if IS_IN (libc)
DIR *
__opendirat (int dfd, const char *name)
{
  if (__glibc_unlikely (invalid_name (name)))
    return NULL;

  if (need_isdir_precheck ())
    {
      /* We first have to check whether the name is for a directory.  We
	 cannot do this after the open() call since the open/close operation
	 performed on, say, a tape device might have undesirable effects.  */
      struct stat64 statbuf;
      if (__glibc_unlikely (__fxstatat64 (_STAT_VER, dfd, name,
					  &statbuf, 0) < 0))
	return NULL;
      if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
	{
	  __set_errno (ENOTDIR);
	  return NULL;
	}
    }

  return opendir_tail (__openat_nocancel (dfd, name, opendir_oflags));
}
#endif


/* Open a directory stream on NAME.  */
DIR *
__opendir (const char *name)
{
  if (__glibc_unlikely (invalid_name (name)))
    return NULL;

  if (need_isdir_precheck ())
    {
      /* We first have to check whether the name is for a directory.  We
	 cannot do this after the open() call since the open/close operation
	 performed on, say, a tape device might have undesirable effects.  */
      struct stat64 statbuf;
      if (__glibc_unlikely (__xstat64 (_STAT_VER, name, &statbuf) < 0))
	return NULL;
      if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
	{
	  __set_errno (ENOTDIR);
	  return NULL;
	}
    }

  return opendir_tail (__open_nocancel (name, opendir_oflags));
}
weak_alias (__opendir, opendir)

DIR *
__alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
{
  /* We have to set the close-on-exit flag if the user provided the
     file descriptor.  */
  if (!close_fd
      && __builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
	goto lose;

  const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
				     ? sizeof (struct dirent64) : 4 * BUFSIZ);
  const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
				   ? sizeof (struct dirent64) : BUFSIZ);
  size_t allocation = default_allocation;
#ifdef _STATBUF_ST_BLKSIZE
  /* Increase allocation if requested, but not if the value appears to
     be bogus.  */
  if (statp != NULL)
    allocation = MIN (MAX ((size_t) statp->st_blksize, default_allocation),
		      MAX_DIR_BUFFER_SIZE);
#endif

  DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
  if (dirp == NULL)
    {
      allocation = small_allocation;
      dirp = (DIR *) malloc (sizeof (DIR) + allocation);

      if (dirp == NULL)
      lose:
	{
	  if (close_fd)
	    {
	      int save_errno = errno;
	      __close_nocancel_nostatus (fd);
	      __set_errno (save_errno);
	    }
	  return NULL;
	}
    }

  dirp->fd = fd;
#if IS_IN (libc)
  __libc_lock_init (dirp->lock);
#endif
  dirp->allocation = allocation;
  dirp->size = 0;
  dirp->offset = 0;
  dirp->filepos = 0;
  dirp->errcode = 0;

  return dirp;
}