1 /* provide a chdir function that tries not to fail due to ENAMETOOLONG 2 Copyright (C) 2004, 2005 Free Software Foundation, Inc. 3 4 This program is free software; you can redistribute it and/or modify 5 it under the terms of the GNU General Public License as published by 6 the Free Software Foundation; either version 2, or (at your option) 7 any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU General Public License for more details. 13 14 You should have received a copy of the GNU General Public License 15 along with this program; if not, write to the Free Software Foundation, 16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 17 18 /* written by Jim Meyering */ 19 20 #ifdef HAVE_CONFIG_H 21 # include <config.h> 22 #endif 23 24 #include "chdir-long.h" 25 26 #include <stdlib.h> 27 #include <stdbool.h> 28 #include <string.h> 29 #include <unistd.h> 30 #include <errno.h> 31 #include <stdio.h> 32 #include <assert.h> 33 #include <limits.h> 34 35 #include "memrchr.h" 36 #include "openat.h" 37 38 #ifndef O_DIRECTORY 39 # define O_DIRECTORY 0 40 #endif 41 42 #ifndef PATH_MAX 43 # error "compile this file only if your system defines PATH_MAX" 44 #endif 45 46 struct cd_buf 47 { 48 int fd; 49 }; 50 51 static inline void 52 cdb_init (struct cd_buf *cdb) 53 { 54 cdb->fd = AT_FDCWD; 55 } 56 57 static inline int 58 cdb_fchdir (struct cd_buf const *cdb) 59 { 60 return fchdir (cdb->fd); 61 } 62 63 static inline void 64 cdb_free (struct cd_buf const *cdb) 65 { 66 if (0 <= cdb->fd) 67 { 68 bool close_fail = close (cdb->fd); 69 assert (! close_fail); 70 } 71 } 72 73 /* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd, 74 try to open the CDB->fd-relative directory, DIR. If the open succeeds, 75 update CDB->fd with the resulting descriptor, close the incoming file 76 descriptor, and return zero. Upon failure, return -1 and set errno. */ 77 static int 78 cdb_advance_fd (struct cd_buf *cdb, char const *dir) 79 { 80 int new_fd = openat (cdb->fd, dir, O_RDONLY | O_DIRECTORY); 81 if (new_fd < 0) 82 { 83 new_fd = openat (cdb->fd, dir, O_WRONLY | O_DIRECTORY); 84 if (new_fd < 0) 85 return -1; 86 } 87 88 cdb_free (cdb); 89 cdb->fd = new_fd; 90 91 return 0; 92 } 93 94 /* Return a pointer to the first non-slash in S. */ 95 static inline char * 96 find_non_slash (char const *s) 97 { 98 size_t n_slash = strspn (s, "/"); 99 return (char *) s + n_slash; 100 } 101 102 /* This is a function much like chdir, but without the PATH_MAX limitation 103 on the length of the directory name. A significant difference is that 104 it must be able to modify (albeit only temporarily) the directory 105 name. It handles an arbitrarily long directory name by operating 106 on manageable portions of the name. On systems without the openat 107 syscall, this means changing the working directory to more and more 108 `distant' points along the long directory name and then restoring 109 the working directory. If any of those attempts to save or restore 110 the working directory fails, this function exits nonzero. 111 112 Note that this function may still fail with errno == ENAMETOOLONG, but 113 only if the specified directory name contains a component that is long 114 enough to provoke such a failure all by itself (e.g. if the component 115 has length PATH_MAX or greater on systems that define PATH_MAX). */ 116 117 int 118 chdir_long (char *dir) 119 { 120 int e = chdir (dir); 121 if (e == 0 || errno != ENAMETOOLONG) 122 return e; 123 124 { 125 size_t len = strlen (dir); 126 char *dir_end = dir + len; 127 struct cd_buf cdb; 128 size_t n_leading_slash; 129 130 cdb_init (&cdb); 131 132 /* If DIR is the empty string, then the chdir above 133 must have failed and set errno to ENOENT. */ 134 assert (0 < len); 135 assert (PATH_MAX <= len); 136 137 /* Count leading slashes. */ 138 n_leading_slash = strspn (dir, "/"); 139 140 /* Handle any leading slashes as well as any name that matches 141 the regular expression, m!^//hostname[/]*! . Handling this 142 prefix separately usually results in a single additional 143 cdb_advance_fd call, but it's worthwhile, since it makes the 144 code in the following loop cleaner. */ 145 if (n_leading_slash == 2) 146 { 147 int err; 148 /* Find next slash. 149 We already know that dir[2] is neither a slash nor '\0'. */ 150 char *slash = memchr (dir + 3, '/', dir_end - (dir + 3)); 151 if (slash == NULL) 152 { 153 errno = ENAMETOOLONG; 154 return -1; 155 } 156 *slash = '\0'; 157 err = cdb_advance_fd (&cdb, dir); 158 *slash = '/'; 159 if (err != 0) 160 goto Fail; 161 dir = find_non_slash (slash + 1); 162 } 163 else if (n_leading_slash) 164 { 165 if (cdb_advance_fd (&cdb, "/") != 0) 166 goto Fail; 167 dir += n_leading_slash; 168 } 169 170 assert (*dir != '/'); 171 assert (dir <= dir_end); 172 173 while (PATH_MAX <= dir_end - dir) 174 { 175 int err; 176 /* Find a slash that is PATH_MAX or fewer bytes away from dir. 177 I.e. see if there is a slash that will give us a name of 178 length PATH_MAX-1 or less. */ 179 char *slash = memrchr (dir, '/', PATH_MAX); 180 if (slash == NULL) 181 { 182 errno = ENAMETOOLONG; 183 return -1; 184 } 185 186 *slash = '\0'; 187 assert (slash - dir < PATH_MAX); 188 err = cdb_advance_fd (&cdb, dir); 189 *slash = '/'; 190 if (err != 0) 191 goto Fail; 192 193 dir = find_non_slash (slash + 1); 194 } 195 196 if (dir < dir_end) 197 { 198 if (cdb_advance_fd (&cdb, dir) != 0) 199 goto Fail; 200 } 201 202 if (cdb_fchdir (&cdb) != 0) 203 goto Fail; 204 205 cdb_free (&cdb); 206 return 0; 207 208 Fail: 209 { 210 int saved_errno = errno; 211 cdb_free (&cdb); 212 errno = saved_errno; 213 return -1; 214 } 215 } 216 } 217 218 #if TEST_CHDIR 219 220 # include <stdio.h> 221 # include "closeout.h" 222 # include "error.h" 223 224 char *program_name; 225 226 int 227 main (int argc, char *argv[]) 228 { 229 char *line = NULL; 230 size_t n = 0; 231 int len; 232 233 program_name = argv[0]; 234 atexit (close_stdout); 235 236 len = getline (&line, &n, stdin); 237 if (len < 0) 238 { 239 int saved_errno = errno; 240 if (feof (stdin)) 241 exit (0); 242 243 error (EXIT_FAILURE, saved_errno, 244 "reading standard input"); 245 } 246 else if (len == 0) 247 exit (0); 248 249 if (line[len-1] == '\n') 250 line[len-1] = '\0'; 251 252 if (chdir_long (line) != 0) 253 error (EXIT_FAILURE, errno, 254 "chdir_long failed: %s", line); 255 256 if (argc <= 1) 257 { 258 /* Using `pwd' here makes sense only if it is a robust implementation, 259 like the one in coreutils after the 2004-04-19 changes. */ 260 char const *cmd = "pwd"; 261 execlp (cmd, (char *) NULL); 262 error (EXIT_FAILURE, errno, "%s", cmd); 263 } 264 265 fclose (stdin); 266 fclose (stderr); 267 268 exit (EXIT_SUCCESS); 269 } 270 #endif 271 272 /* 273 Local Variables: 274 compile-command: "gcc -DTEST_CHDIR=1 -DHAVE_CONFIG_H -I.. -g -O -W -Wall chdir-long.c libcoreutils.a" 275 End: 276 */ 277