summaryrefslogtreecommitdiff
path: root/lib/chdir-long.c
blob: 8c15d06d2a99de89c100c2f216c6721e071b2913 (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
/* provide a chdir function that tries not to fail due to ENAMETOOLONG
   Copyright (C) 2004, 2005 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 "chdir-long.h"

#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <assert.h>
#include <limits.h>

#include "memrchr.h"
#include "openat.h"

#ifndef O_DIRECTORY
# define O_DIRECTORY 0
#endif

#ifndef PATH_MAX
# error "compile this file only if your system defines PATH_MAX"
#endif

struct cd_buf
{
  int fd;
};

static inline void
cdb_init (struct cd_buf *cdb)
{
  cdb->fd = AT_FDCWD;
}

static inline int
cdb_fchdir (struct cd_buf const *cdb)
{
  return fchdir (cdb->fd);
}

static inline void
cdb_free (struct cd_buf const *cdb)
{
  if (0 <= cdb->fd)
    {
      bool close_fail = close (cdb->fd);
      assert (! close_fail);
    }
}

/* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
   try to open the CDB->fd-relative directory, DIR.  If the open succeeds,
   update CDB->fd with the resulting descriptor, close the incoming file
   descriptor, and return zero.  Upon failure, return -1 and set errno.  */
static int
cdb_advance_fd (struct cd_buf *cdb, char const *dir)
{
  int new_fd = openat (cdb->fd, dir,
		       O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
  if (new_fd < 0)
    return -1;

  cdb_free (cdb);
  cdb->fd = new_fd;

  return 0;
}

/* Return a pointer to the first non-slash in S.  */
static inline char *
find_non_slash (char const *s)
{
  size_t n_slash = strspn (s, "/");
  return (char *) s + n_slash;
}

/* This is a function much like chdir, but without the PATH_MAX limitation
   on the length of the directory name.  A significant difference is that
   it must be able to modify (albeit only temporarily) the directory
   name.  It handles an arbitrarily long directory name by operating
   on manageable portions of the name.  On systems without the openat
   syscall, this means changing the working directory to more and more
   `distant' points along the long directory name and then restoring
   the working directory.  If any of those attempts to save or restore
   the working directory fails, this function exits nonzero.

   Note that this function may still fail with errno == ENAMETOOLONG, but
   only if the specified directory name contains a component that is long
   enough to provoke such a failure all by itself (e.g. if the component
   has length PATH_MAX or greater on systems that define PATH_MAX).  */

int
chdir_long (char *dir)
{
  int e = chdir (dir);
  if (e == 0 || errno != ENAMETOOLONG)
    return e;

  {
    size_t len = strlen (dir);
    char *dir_end = dir + len;
    struct cd_buf cdb;
    size_t n_leading_slash;

    cdb_init (&cdb);

    /* If DIR is the empty string, then the chdir above
       must have failed and set errno to ENOENT.  */
    assert (0 < len);
    assert (PATH_MAX <= len);

    /* Count leading slashes.  */
    n_leading_slash = strspn (dir, "/");

    /* Handle any leading slashes as well as any name that matches
       the regular expression, m!^//hostname[/]*! .  Handling this
       prefix separately usually results in a single additional
       cdb_advance_fd call, but it's worthwhile, since it makes the
       code in the following loop cleaner.  */
    if (n_leading_slash == 2)
      {
	int err;
	/* Find next slash.
	   We already know that dir[2] is neither a slash nor '\0'.  */
	char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
	if (slash == NULL)
	  {
	    errno = ENAMETOOLONG;
	    return -1;
	  }
	*slash = '\0';
	err = cdb_advance_fd (&cdb, dir);
	*slash = '/';
	if (err != 0)
	  goto Fail;
	dir = find_non_slash (slash + 1);
      }
    else if (n_leading_slash)
      {
	if (cdb_advance_fd (&cdb, "/") != 0)
	  goto Fail;
	dir += n_leading_slash;
      }

    assert (*dir != '/');
    assert (dir <= dir_end);

    while (PATH_MAX <= dir_end - dir)
      {
	int err;
	/* Find a slash that is PATH_MAX or fewer bytes away from dir.
	   I.e. see if there is a slash that will give us a name of
	   length PATH_MAX-1 or less.  */
	char *slash = memrchr (dir, '/', PATH_MAX);
	if (slash == NULL)
	  {
	    errno = ENAMETOOLONG;
	    return -1;
	  }

	*slash = '\0';
	assert (slash - dir < PATH_MAX);
	err = cdb_advance_fd (&cdb, dir);
	*slash = '/';
	if (err != 0)
	  goto Fail;

	dir = find_non_slash (slash + 1);
      }

    if (dir < dir_end)
      {
	if (cdb_advance_fd (&cdb, dir) != 0)
	  goto Fail;
      }

    if (cdb_fchdir (&cdb) != 0)
      goto Fail;

    cdb_free (&cdb);
    return 0;

   Fail:
    {
      int saved_errno = errno;
      cdb_free (&cdb);
      errno = saved_errno;
      return -1;
    }
  }
}

#if TEST_CHDIR

# include <stdio.h>
# include "closeout.h"
# include "error.h"

char *program_name;

int
main (int argc, char *argv[])
{
  char *line = NULL;
  size_t n = 0;
  int len;

  program_name = argv[0];
  atexit (close_stdout);

  len = getline (&line, &n, stdin);
  if (len < 0)
    {
      int saved_errno = errno;
      if (feof (stdin))
	exit (0);

      error (EXIT_FAILURE, saved_errno,
	     "reading standard input");
    }
  else if (len == 0)
    exit (0);

  if (line[len-1] == '\n')
    line[len-1] = '\0';

  if (chdir_long (line) != 0)
    error (EXIT_FAILURE, errno,
	   "chdir_long failed: %s", line);

  if (argc <= 1)
    {
      /* Using `pwd' here makes sense only if it is a robust implementation,
	 like the one in coreutils after the 2004-04-19 changes.  */
      char const *cmd = "pwd";
      execlp (cmd, (char *) NULL);
      error (EXIT_FAILURE, errno, "%s", cmd);
    }

  fclose (stdin);
  fclose (stderr);

  exit (EXIT_SUCCESS);
}
#endif

/*
Local Variables:
compile-command: "gcc -DTEST_CHDIR=1 -DHAVE_CONFIG_H -I.. -g -O -W -Wall chdir-long.c libcoreutils.a"
End:
*/