summaryrefslogtreecommitdiff
path: root/lib/openat.c
blob: ca71d658e87e1703d4cb840ecde3bd235caaa80f (plain)
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
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
/* provide a replacement openat function
   Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* written by Jim Meyering */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include "openat.h"

#include <stdarg.h>
#include <stddef.h>

#include "dirname.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
#include "fcntl--.h"
#include "lstat.h"
#include "openat-priv.h"
#include "save-cwd.h"

/* Replacement for Solaris' openat function.
   <http://www.google.com/search?q=openat+site:docs.sun.com>
   First, try to simulate it via open ("/proc/self/fd/FD/FILE").
   Failing that, simulate it by doing save_cwd/fchdir/open/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely),
   then give a diagnostic and exit nonzero.
   Otherwise, upon failure, set errno and return -1, as openat does.
   Upon successful completion, return a file descriptor.  */
int
openat (int fd, char const *file, int flags, ...)
{
  mode_t mode = 0;

  if (flags & O_CREAT)
    {
      va_list arg;
      va_start (arg, flags);

      /* If mode_t is narrower than int, use the promoted type (int),
         not mode_t.  Use sizeof to guess whether mode_t is narrower;
         we don't know of any practical counterexamples.  */
      mode = (sizeof (mode_t) < sizeof (int)
	      ? va_arg (arg, int)
	      : va_arg (arg, mode_t));

      va_end (arg);
    }

  return openat_permissive (fd, file, flags, mode, NULL);
}

/* Like openat (FD, FILE, FLAGS, MODE), but if CWD_ERRNO is
   nonnull, set *CWD_ERRNO to an errno value if unable to save
   or restore the initial working directory.  This is needed only
   the first time remove.c's remove_dir opens a command-line
   directory argument.

   If a previous attempt to restore the current working directory
   failed, then we must not even try to access a `.'-relative name.
   It is the caller's responsibility not to call this function
   in that case.  */

int
openat_permissive (int fd, char const *file, int flags, mode_t mode,
		   int *cwd_errno)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  int err;
  bool save_ok;

  if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
    return open (file, flags, mode);

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, file);
    err = open (proc_file, flags, mode);
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (0 <= err || ! EXPECTED_ERRNO (errno))
      return err;
  }

  save_ok = (save_cwd (&saved_cwd) == 0);
  if (! save_ok)
    {
      if (! cwd_errno)
	openat_save_fail (errno);
      *cwd_errno = errno;
    }

  err = fchdir (fd);
  saved_errno = errno;

  if (! err)
    {
      err = open (file, flags, mode);
      saved_errno = errno;
      if (save_ok && restore_cwd (&saved_cwd) != 0)
	{
	  if (! cwd_errno)
	    openat_restore_fail (errno);
	  *cwd_errno = errno;
	}
    }

  free_cwd (&saved_cwd);
  errno = saved_errno;
  return err;
}

/* Return true if our openat implementation must resort to
   using save_cwd and restore_cwd.  */
bool
openat_needs_fchdir (void)
{
  int fd2;
  int fd = open ("/", O_RDONLY);
  char *proc_file;

  if (fd < 0)
    return true;
  BUILD_PROC_NAME (proc_file, fd, ".");
  fd2 = open (proc_file, O_RDONLY);
  close (fd);
  if (0 <= fd2)
    close (fd2);

  return fd2 < 0;
}

#if !HAVE_FDOPENDIR

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=fdopendir+site:docs.sun.com>
   First, try to simulate it via opendir ("/proc/self/fd/FD").  Failing
   that, simulate it by doing save_cwd/fchdir/opendir(".")/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' fdopendir.

   W A R N I N G:
   Unlike the other fd-related functions here, this one
   effectively consumes its FD parameter.  The caller should not
   close or otherwise manipulate FD if this function returns successfully.  */
DIR *
fdopendir (int fd)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  DIR *dir;

  char *proc_file;
  BUILD_PROC_NAME (proc_file, fd, ".");
  dir = opendir (proc_file);
  saved_errno = errno;

  /* If the syscall fails with an expected errno value, resort to
     save_cwd/restore_cwd.  */
  if (! dir && EXPECTED_ERRNO (saved_errno))
    {
      if (save_cwd (&saved_cwd) != 0)
	openat_save_fail (errno);

      if (fchdir (fd) != 0)
	{
	  dir = NULL;
	  saved_errno = errno;
	}
      else
	{
	  dir = opendir (".");
	  saved_errno = errno;

	  if (restore_cwd (&saved_cwd) != 0)
	    openat_restore_fail (errno);
	}

      free_cwd (&saved_cwd);
    }

  if (dir)
    close (fd);
  errno = saved_errno;
  return dir;
}

#endif

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=fstatat+site:docs.sun.com>
   First, try to simulate it via l?stat ("/proc/self/fd/FD/FILE").
   Failing that, simulate it via save_cwd/fchdir/(stat|lstat)/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' fstatat.  */

#define AT_FUNC_NAME fstatat
#define AT_FUNC_F1 lstat
#define AT_FUNC_F2 stat
#define AT_FUNC_USE_F1_COND flag == AT_SYMLINK_NOFOLLOW
#define AT_FUNC_POST_FILE_PARAM_DECLS , struct stat *st, int flag
#define AT_FUNC_POST_FILE_ARGS        , st
#include "at-func.c"
#undef AT_FUNC_NAME
#undef AT_FUNC_F1
#undef AT_FUNC_F2
#undef AT_FUNC_USE_F1_COND
#undef AT_FUNC_POST_FILE_PARAM_DECLS
#undef AT_FUNC_POST_FILE_ARGS

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=unlinkat+site:docs.sun.com>
   First, try to simulate it via (unlink|rmdir) ("/proc/self/fd/FD/FILE").
   Failing that, simulate it via save_cwd/fchdir/(unlink|rmdir)/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' unlinkat.  */

#define AT_FUNC_NAME unlinkat
#define AT_FUNC_F1 rmdir
#define AT_FUNC_F2 unlink
#define AT_FUNC_USE_F1_COND flag == AT_REMOVEDIR
#define AT_FUNC_POST_FILE_PARAM_DECLS , int flag
#define AT_FUNC_POST_FILE_ARGS        /* empty */
#include "at-func.c"
#undef AT_FUNC_NAME
#undef AT_FUNC_F1
#undef AT_FUNC_F2
#undef AT_FUNC_USE_F1_COND
#undef AT_FUNC_POST_FILE_PARAM_DECLS
#undef AT_FUNC_POST_FILE_ARGS

/* Replacement for Solaris' function by the same name.
   Invoke chown or lchown on file, FILE, using OWNER and GROUP, in the
   directory open on descriptor FD.  If FLAG is AT_SYMLINK_NOFOLLOW, then
   use lchown, otherwise, use chown.  If possible, do it without changing
   the working directory.  Otherwise, resort to using save_cwd/fchdir,
   then mkdir/restore_cwd.  If either the save_cwd or the restore_cwd
   fails, then give a diagnostic and exit nonzero.  */

#define AT_FUNC_NAME fchownat
#define AT_FUNC_F1 lchown
#define AT_FUNC_F2 chown
#define AT_FUNC_USE_F1_COND flag == AT_SYMLINK_NOFOLLOW
#define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group, int flag
#define AT_FUNC_POST_FILE_ARGS        , owner, group
#include "at-func.c"