lib/libc/stdlib/realpath.c

   1 /*
   2  * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  * 3. The names of the authors may not be used to endorse or promote
  13  *    products derived from this software without specific prior written
  14  *    permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28
  29 #if defined(LIBC_SCCS) && !defined(lint)
  30 static char sccsid[] = "@(#)realpath.c  8.1 (Berkeley) 2/16/94";
  31 #endif /* LIBC_SCCS and not lint */
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include "namespace.h"
  36 #include <sys/param.h>
  37 #include <sys/stat.h>
  38
  39 #include <errno.h>
  40 #include <stdlib.h>
  41 #include <string.h>
  42 #include <unistd.h>
  43 #include "un-namespace.h"
  44
  45 /*
  46  * Find the real name of path, by removing all ".", ".." and symlink
  47  * components.  Returns (resolved) on success, or (NULL) on failure,
  48  * in which case the path which caused trouble is left in (resolved).
  49  */
  50 char *
  51 realpath(const char * __restrict path, char * __restrict resolved)
  52 {
  53         struct stat sb;
  54         char *p, *q, *s;
  55         size_t left_len, resolved_len;
  56         unsigned symlinks;
  57         int serrno, slen, m;
  58         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  59
  60         if (path == NULL) {
  61                 errno = EINVAL;
  62                 return (NULL);
  63         }
  64         if (path[0] == '\0') {
  65                 errno = ENOENT;
  66                 return (NULL);
  67         }
  68         serrno = errno;
  69         if (resolved == NULL) {
  70                 resolved = malloc(PATH_MAX);
  71                 if (resolved == NULL)
  72                         return (NULL);
  73                 m = 1;
  74         } else
  75                 m = 0;
  76
  77         symlinks = 0;
  78         if (path[0] == '/') {
  79                 resolved[0] = '/';
  80                 resolved[1] = '\0';
  81                 if (path[1] == '\0')
  82                         return (resolved);
  83                 resolved_len = 1;
  84                 left_len = strlcpy(left, path + 1, sizeof(left));
  85         } else {
  86                 if (getcwd(resolved, PATH_MAX) == NULL) {
  87                         if (m)
  88                                 free(resolved);
  89                         else
  90                                 strlcpy(resolved, ".", PATH_MAX);
  91                         return (NULL);
  92                 }
  93                 resolved_len = strlen(resolved);
  94                 left_len = strlcpy(left, path, sizeof(left));
  95         }
  96         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  97                 if (m)
  98                         free(resolved);
  99                 errno = ENAMETOOLONG;
 100                 return (NULL);
 101         }
 102
 103         /*
 104          * Iterate over path components in `left'.
 105          */
 106         while (left_len != 0) {
 107                 /*
 108                  * Extract the next path component and adjust `left'
 109                  * and its length.
 110                  */
 111                 p = strchr(left, '/');
 112                 s = p ? p : left + left_len;
 113                 if (s - left >= sizeof(next_token)) {
 114                         if (m)
 115                                 free(resolved);
 116                         errno = ENAMETOOLONG;
 117                         return (NULL);
 118                 }
 119                 memcpy(next_token, left, s - left);
 120                 next_token[s - left] = '\0';
 121                 left_len -= s - left;
 122                 if (p != NULL)
 123                         memmove(left, s + 1, left_len + 1);
 124                 if (resolved[resolved_len - 1] != '/') {
 125                         if (resolved_len + 1 >= PATH_MAX) {
 126                                 if (m)
 127                                         free(resolved);
 128                                 errno = ENAMETOOLONG;
 129                                 return (NULL);
 130                         }
 131                         resolved[resolved_len++] = '/';
 132                         resolved[resolved_len] = '\0';
 133                 }
 134                 if (next_token[0] == '\0')
 135                         continue;
 136                 else if (strcmp(next_token, ".") == 0)
 137                         continue;
 138                 else if (strcmp(next_token, "..") == 0) {
 139                         /*
 140                          * Strip the last path component except when we have
 141                          * single "/"
 142                          */
 143                         if (resolved_len > 1) {
 144                                 resolved[resolved_len - 1] = '\0';
 145                                 q = strrchr(resolved, '/') + 1;
 146                                 *q = '\0';
 147                                 resolved_len = q - resolved;
 148                         }
 149                         continue;
 150                 }
 151
 152                 /*
 153                  * Append the next path component and lstat() it. If
 154                  * lstat() fails we still can return successfully if
 155                  * there are no more path components left.
 156                  */
 157                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 158                 if (resolved_len >= PATH_MAX) {
 159                         if (m)
 160                                 free(resolved);
 161                         errno = ENAMETOOLONG;
 162                         return (NULL);
 163                 }
 164                 if (lstat(resolved, &sb) != 0) {
 165                         if (errno == ENOENT && p == NULL) {
 166                                 errno = serrno;
 167                                 return (resolved);
 168                         }
 169                         if (m)
 170                                 free(resolved);
 171                         return (NULL);
 172                 }
 173                 if (S_ISLNK(sb.st_mode)) {
 174                         if (symlinks++ > MAXSYMLINKS) {
 175                                 if (m)
 176                                         free(resolved);
 177                                 errno = ELOOP;
 178                                 return (NULL);
 179                         }
 180                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 181                         if (slen < 0) {
 182                                 if (m)
 183                                         free(resolved);
 184                                 return (NULL);
 185                         }
 186                         symlink[slen] = '\0';
 187                         if (symlink[0] == '/') {
 188                                 resolved[1] = 0;
 189                                 resolved_len = 1;
 190                         } else if (resolved_len > 1) {
 191                                 /* Strip the last path component. */
 192                                 resolved[resolved_len - 1] = '\0';
 193                                 q = strrchr(resolved, '/') + 1;
 194                                 *q = '\0';
 195                                 resolved_len = q - resolved;
 196                         }
 197
 198                         /*
 199                          * If there are any path components left, then
 200                          * append them to symlink. The result is placed
 201                          * in `left'.
 202                          */
 203                         if (p != NULL) {
 204                                 if (symlink[slen - 1] != '/') {
 205                                         if (slen + 1 >= sizeof(symlink)) {
 206                                                 if (m)
 207                                                         free(resolved);
 208                                                 errno = ENAMETOOLONG;
 209                                                 return (NULL);
 210                                         }
 211                                         symlink[slen] = '/';
 212                                         symlink[slen + 1] = 0;
 213                                 }
 214                                 left_len = strlcat(symlink, left, sizeof(left));
 215                                 if (left_len >= sizeof(left)) {
 216                                         if (m)
 217                                                 free(resolved);
 218                                         errno = ENAMETOOLONG;
 219                                         return (NULL);
 220                                 }
 221                         }
 222                         left_len = strlcpy(left, symlink, sizeof(left));
 223                 }
 224         }
 225
 226         /*
 227          * Remove trailing slash except when the resolved pathname
 228          * is a single "/".
 229          */
 230         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 231                 resolved[resolved_len - 1] = '\0';
 232         return (resolved);
 233 }