summaryrefslogtreecommitdiffstats
path: root/lib/openat.c
blob: 52aab19d2732707b7b9fe035cbedeed008ac84dd (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
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
/* provide a replacement openat function
   Copyright (C) 2004-2022 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 3 of the License, 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, see <https://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

/* If the user's config.h happens to include <fcntl.h>, let it include only
   the system's <fcntl.h> here, so that orig_openat doesn't recurse to
   rpl_openat.  */
#define __need_system_fcntl_h
#include <config.h>

/* Get the original definition of open.  It might be defined as a macro.  */
#include <fcntl.h>
#include <sys/types.h>
#undef __need_system_fcntl_h

#if HAVE_OPENAT
static int
orig_openat (int fd, char const *filename, int flags, mode_t mode)
{
  return openat (fd, filename, flags, mode);
}
#endif

/* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
   this include because of the preliminary #include <fcntl.h> above.  */
#include "fcntl.h"

#include "openat.h"

#include "cloexec.h"

#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <errno.h>

#if HAVE_OPENAT

/* Like openat, but support O_CLOEXEC and work around Solaris 9 bugs
   with trailing slash.  */
int
rpl_openat (int dfd, char const *filename, int flags, ...)
{
  /* 0 = unknown, 1 = yes, -1 = no.  */
#if GNULIB_defined_O_CLOEXEC
  int have_cloexec = -1;
#else
  static int have_cloexec;
#endif

  mode_t mode;
  int fd;

  mode = 0;
  if (flags & O_CREAT)
    {
      va_list arg;
      va_start (arg, flags);

      /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
         creates crashing code when 'mode_t' is smaller than 'int'.  */
      mode = va_arg (arg, PROMOTED_MODE_T);

      va_end (arg);
    }

# if OPEN_TRAILING_SLASH_BUG
  /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
     ends in a slash, as POSIX says such a filename must name a directory
     <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
       "A pathname that contains at least one non-<slash> character and that
        ends with one or more trailing <slash> characters shall not be resolved
        successfully unless the last pathname component before the trailing
        <slash> characters names an existing directory"
     If the named file already exists as a directory, then
       - if O_CREAT is specified, open() must fail because of the semantics
         of O_CREAT,
       - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
         <https://pubs.opengroup.org/onlinepubs/9699919799/functions/openat.html>
         says that it fails with errno = EISDIR in this case.
     If the named file does not exist or does not name a directory, then
       - if O_CREAT is specified, open() must fail since open() cannot create
         directories,
       - if O_WRONLY or O_RDWR is specified, open() must fail because the
         file does not contain a '.' directory.  */
  if ((flags & O_CREAT)
      || (flags & O_ACCMODE) == O_RDWR
      || (flags & O_ACCMODE) == O_WRONLY)
    {
      size_t len = strlen (filename);
      if (len > 0 && filename[len - 1] == '/')
        {
          errno = EISDIR;
          return -1;
        }
    }
# endif

  fd = orig_openat (dfd, filename,
                    flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);

  if (flags & O_CLOEXEC)
    {
      if (! have_cloexec)
        {
          if (0 <= fd)
            have_cloexec = 1;
          else if (errno == EINVAL)
            {
              fd = orig_openat (dfd, filename, flags & ~O_CLOEXEC, mode);
              have_cloexec = -1;
            }
        }
      if (have_cloexec < 0 && 0 <= fd)
        set_cloexec_flag (fd, true);
    }


# if OPEN_TRAILING_SLASH_BUG
  /* If the filename ends in a slash and fd does not refer to a directory,
     then fail.
     Rationale: POSIX says such a filename must name a directory
     <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
       "A pathname that contains at least one non-<slash> character and that
        ends with one or more trailing <slash> characters shall not be resolved
        successfully unless the last pathname component before the trailing
        <slash> characters names an existing directory"
     If the named file without the slash is not a directory, open() must fail
     with ENOTDIR.  */
  if (fd >= 0)
    {
      /* We know len is positive, since open did not fail with ENOENT.  */
      size_t len = strlen (filename);
      if (filename[len - 1] == '/')
        {
          struct stat statbuf;

          if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
            {
              close (fd);
              errno = ENOTDIR;
              return -1;
            }
        }
    }
# endif

  return fd;
}

#else /* !HAVE_OPENAT */

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

/* Replacement for Solaris' openat function.
   <https://www.google.com/search?q=openat+site:docs.oracle.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);

      /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
         creates crashing code when 'mode_t' is smaller than 'int'.  */
      mode = va_arg (arg, PROMOTED_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 buf[OPENAT_BUFFER_SIZE];
    char *proc_file = openat_proc_name (buf, fd, file);
    if (proc_file)
      {
        int open_result = open (proc_file, flags, mode);
        int open_errno = errno;
        if (proc_file != buf)
          free (proc_file);
        /* 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 <= open_result || ! EXPECTED_ERRNO (open_errno))
          {
            errno = open_errno;
            return open_result;
          }
      }
  }

  save_ok = (save_cwd (&saved_cwd) == 0);
  if (! save_ok)
    {
      if (! cwd_errno)
        openat_save_fail (errno);
      *cwd_errno = errno;
    }
  if (0 <= fd && fd == saved_cwd.desc)
    {
      /* If saving the working directory collides with the user's
         requested fd, then the user's fd must have been closed to
         begin with.  */
      free_cwd (&saved_cwd);
      errno = EBADF;
      return -1;
    }

  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)
            {
              /* Don't write a message to just-created fd 2.  */
              saved_errno = errno;
              if (err == STDERR_FILENO)
                close (err);
              openat_restore_fail (saved_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)
{
  bool needs_fchdir = true;
  int fd = open ("/", O_SEARCH | O_CLOEXEC);

  if (0 <= fd)
    {
      char buf[OPENAT_BUFFER_SIZE];
      char *proc_file = openat_proc_name (buf, fd, ".");
      if (proc_file)
        {
          needs_fchdir = false;
          if (proc_file != buf)
            free (proc_file);
        }
      close (fd);
    }

  return needs_fchdir;
}

#endif /* !HAVE_OPENAT */