u-tools/apps/tar/gnu/chdir-long.c

   1 /* -*- buffer-read-only: t -*- vi: set ro: */
   2 /* DO NOT EDIT! GENERATED AUTOMATICALLY! */
   3 /* provide a chdir function that tries not to fail due to ENAMETOOLONG
   4    Copyright (C) 2004-2011 Free Software Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 #include "chdir-long.h"
  24
  25 #include <assert.h>
  26 #include <errno.h>
  27 #include <fcntl.h>
  28 #include <stdlib.h>
  29 #include <stdbool.h>
  30 #include <string.h>
  31 #include <stdio.h>
  32
  33 #ifndef PATH_MAX
  34 # error "compile this file only if your system defines PATH_MAX"
  35 #endif
  36
  37 /* The results of openat() in this file are not leaked to any
  38    single-threaded code that could use stdio.
  39    FIXME - if the kernel ever adds support for multi-thread safety for
  40    avoiding standard fds, then we should use openat_safer.  */
  41
  42 struct cd_buf
  43 {
  44   int fd;
  45 };
  46
  47 static inline void
  48 cdb_init (struct cd_buf *cdb)
  49 {
  50   cdb->fd = AT_FDCWD;
  51 }
  52
  53 static inline int
  54 cdb_fchdir (struct cd_buf const *cdb)
  55 {
  56   return fchdir (cdb->fd);
  57 }
  58
  59 static inline void
  60 cdb_free (struct cd_buf const *cdb)
  61 {
  62   if (0 <= cdb->fd)
  63     {
  64       bool close_fail = close (cdb->fd);
  65       assert (! close_fail);
  66     }
  67 }
  68
  69 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
  70    try to open the CDB->fd-relative directory, DIR.  If the open succeeds,
  71    update CDB->fd with the resulting descriptor, close the incoming file
  72    descriptor, and return zero.  Upon failure, return -1 and set errno.  */
  73 static int
  74 cdb_advance_fd (struct cd_buf *cdb, char const *dir)
  75 {
  76   int new_fd = openat (cdb->fd, dir,
  77                        O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
  78   if (new_fd < 0)
  79     return -1;
  80
  81   cdb_free (cdb);
  82   cdb->fd = new_fd;
  83
  84   return 0;
  85 }
  86
  87 /* Return a pointer to the first non-slash in S.  */
  88 static inline char *
  89 find_non_slash (char const *s)
  90 {
  91   size_t n_slash = strspn (s, "/");
  92   return (char *) s + n_slash;
  93 }
  94
  95 /* This is a function much like chdir, but without the PATH_MAX limitation
  96    on the length of the directory name.  A significant difference is that
  97    it must be able to modify (albeit only temporarily) the directory
  98    name.  It handles an arbitrarily long directory name by operating
  99    on manageable portions of the name.  On systems without the openat
 100    syscall, this means changing the working directory to more and more
 101    `distant' points along the long directory name and then restoring
 102    the working directory.  If any of those attempts to save or restore
 103    the working directory fails, this function exits nonzero.
 104
 105    Note that this function may still fail with errno == ENAMETOOLONG, but
 106    only if the specified directory name contains a component that is long
 107    enough to provoke such a failure all by itself (e.g. if the component
 108    has length PATH_MAX or greater on systems that define PATH_MAX).  */
 109
 110 int
 111 chdir_long (char *dir)
 112 {
 113   int e = chdir (dir);
 114   if (e == 0 || errno != ENAMETOOLONG)
 115     return e;
 116
 117   {
 118     size_t len = strlen (dir);
 119     char *dir_end = dir + len;
 120     struct cd_buf cdb;
 121     size_t n_leading_slash;
 122
 123     cdb_init (&cdb);
 124
 125     /* If DIR is the empty string, then the chdir above
 126        must have failed and set errno to ENOENT.  */
 127     assert (0 < len);
 128     assert (PATH_MAX <= len);
 129
 130     /* Count leading slashes.  */
 131     n_leading_slash = strspn (dir, "/");
 132
 133     /* Handle any leading slashes as well as any name that matches
 134        the regular expression, m!^//hostname[/]*! .  Handling this
 135        prefix separately usually results in a single additional
 136        cdb_advance_fd call, but it's worthwhile, since it makes the
 137        code in the following loop cleaner.  */
 138     if (n_leading_slash == 2)
 139       {
 140         int err;
 141         /* Find next slash.
 142            We already know that dir[2] is neither a slash nor '\0'.  */
 143         char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
 144         if (slash == NULL)
 145           {
 146             errno = ENAMETOOLONG;
 147             return -1;
 148           }
 149         *slash = '\0';
 150         err = cdb_advance_fd (&cdb, dir);
 151         *slash = '/';
 152         if (err != 0)
 153           goto Fail;
 154         dir = find_non_slash (slash + 1);
 155       }
 156     else if (n_leading_slash)
 157       {
 158         if (cdb_advance_fd (&cdb, "/") != 0)
 159           goto Fail;
 160         dir += n_leading_slash;
 161       }
 162
 163     assert (*dir != '/');
 164     assert (dir <= dir_end);
 165
 166     while (PATH_MAX <= dir_end - dir)
 167       {
 168         int err;
 169         /* Find a slash that is PATH_MAX or fewer bytes away from dir.
 170            I.e. see if there is a slash that will give us a name of
 171            length PATH_MAX-1 or less.  */
 172         char *slash = memrchr (dir, '/', PATH_MAX);
 173         if (slash == NULL)
 174           {
 175             errno = ENAMETOOLONG;
 176             return -1;
 177           }
 178
 179         *slash = '\0';
 180         assert (slash - dir < PATH_MAX);
 181         err = cdb_advance_fd (&cdb, dir);
 182         *slash = '/';
 183         if (err != 0)
 184           goto Fail;
 185
 186         dir = find_non_slash (slash + 1);
 187       }
 188
 189     if (dir < dir_end)
 190       {
 191         if (cdb_advance_fd (&cdb, dir) != 0)
 192           goto Fail;
 193       }
 194
 195     if (cdb_fchdir (&cdb) != 0)
 196       goto Fail;
 197
 198     cdb_free (&cdb);
 199     return 0;
 200
 201    Fail:
 202     {
 203       int saved_errno = errno;
 204       cdb_free (&cdb);
 205       errno = saved_errno;
 206       return -1;
 207     }
 208   }
 209 }
 210
 211 #if TEST_CHDIR
 212
 213 # include "closeout.h"
 214 # include "error.h"
 215
 216 char *program_name;
 217
 218 int
 219 main (int argc, char *argv[])
 220 {
 221   char *line = NULL;
 222   size_t n = 0;
 223   int len;
 224
 225   program_name = argv[0];
 226   atexit (close_stdout);
 227
 228   len = getline (&line, &n, stdin);
 229   if (len < 0)
 230     {
 231       int saved_errno = errno;
 232       if (feof (stdin))
 233         exit (0);
 234
 235       error (EXIT_FAILURE, saved_errno,
 236              "reading standard input");
 237     }
 238   else if (len == 0)
 239     exit (0);
 240
 241   if (line[len-1] == '\n')
 242     line[len-1] = '\0';
 243
 244   if (chdir_long (line) != 0)
 245     error (EXIT_FAILURE, errno,
 246            "chdir_long failed: %s", line);
 247
 248   if (argc <= 1)
 249     {
 250       /* Using `pwd' here makes sense only if it is a robust implementation,
 251          like the one in coreutils after the 2004-04-19 changes.  */
 252       char const *cmd = "pwd";
 253       execlp (cmd, (char *) NULL);
 254       error (EXIT_FAILURE, errno, "%s", cmd);
 255     }
 256
 257   fclose (stdin);
 258   fclose (stderr);
 259
 260   exit (EXIT_SUCCESS);
 261 }
 262 #endif
 263
 264 /*
 265 Local Variables:
 266 compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"
 267 End:
 268 */