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 m, slen;
  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         if (resolved == NULL) {
  69                 resolved = malloc(PATH_MAX);
  70                 if (resolved == NULL)
  71                         return (NULL);
  72                 m = 1;
  73         } else
  74                 m = 0;
  75         symlinks = 0;
  76         if (path[0] == '/') {
  77                 resolved[0] = '/';
  78                 resolved[1] = '\0';
  79                 if (path[1] == '\0')
  80                         return (resolved);
  81                 resolved_len = 1;
  82                 left_len = strlcpy(left, path + 1, sizeof(left));
  83         } else {
  84                 if (getcwd(resolved, PATH_MAX) == NULL) {
  85                         if (m)
  86                                 free(resolved);
  87                         else {
  88                                 resolved[0] = '.';
  89                                 resolved[1] = '\0';
  90                         }
  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                         /*
 136                          * Handle consequential slashes.  The path
 137                          * before slash shall point to a directory.
 138                          *
 139                          * Only the trailing slashes are not covered
 140                          * by other checks in the loop, but we verify
 141                          * the prefix for any (rare) "//" or "/\0"
 142                          * occurrence to not implement lookahead.
 143                          */
 144                         if (lstat(resolved, &sb) != 0) {
 145                                 if (m)
 146                                         free(resolved);
 147                                 return (NULL);
 148                         }
 149                         if (!S_ISDIR(sb.st_mode)) {
 150                                 if (m)
 151                                         free(resolved);
 152                                 errno = ENOTDIR;
 153                                 return (NULL);
 154                         }
 155                         continue;
 156                 }
 157                 else if (strcmp(next_token, ".") == 0)
 158                         continue;
 159                 else if (strcmp(next_token, "..") == 0) {
 160                         /*
 161                          * Strip the last path component except when we have
 162                          * single "/"
 163                          */
 164                         if (resolved_len > 1) {
 165                                 resolved[resolved_len - 1] = '\0';
 166                                 q = strrchr(resolved, '/') + 1;
 167                                 *q = '\0';
 168                                 resolved_len = q - resolved;
 169                         }
 170                         continue;
 171                 }
 172
 173                 /*
 174                  * Append the next path component and lstat() it.
 175                  */
 176                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 177                 if (resolved_len >= PATH_MAX) {
 178                         if (m)
 179                                 free(resolved);
 180                         errno = ENAMETOOLONG;
 181                         return (NULL);
 182                 }
 183                 if (lstat(resolved, &sb) != 0) {
 184                         if (m)
 185                                 free(resolved);
 186                         return (NULL);
 187                 }
 188                 if (S_ISLNK(sb.st_mode)) {
 189                         if (symlinks++ > MAXSYMLINKS) {
 190                                 if (m)
 191                                         free(resolved);
 192                                 errno = ELOOP;
 193                                 return (NULL);
 194                         }
 195                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 196                         if (slen < 0) {
 197                                 if (m)
 198                                         free(resolved);
 199                                 return (NULL);
 200                         }
 201                         symlink[slen] = '\0';
 202                         if (symlink[0] == '/') {
 203                                 resolved[1] = 0;
 204                                 resolved_len = 1;
 205                         } else if (resolved_len > 1) {
 206                                 /* Strip the last path component. */
 207                                 resolved[resolved_len - 1] = '\0';
 208                                 q = strrchr(resolved, '/') + 1;
 209                                 *q = '\0';
 210                                 resolved_len = q - resolved;
 211                         }
 212
 213                         /*
 214                          * If there are any path components left, then
 215                          * append them to symlink. The result is placed
 216                          * in `left'.
 217                          */
 218                         if (p != NULL) {
 219                                 if (symlink[slen - 1] != '/') {
 220                                         if (slen + 1 >= sizeof(symlink)) {
 221                                                 if (m)
 222                                                         free(resolved);
 223                                                 errno = ENAMETOOLONG;
 224                                                 return (NULL);
 225                                         }
 226                                         symlink[slen] = '/';
 227                                         symlink[slen + 1] = 0;
 228                                 }
 229                                 left_len = strlcat(symlink, left,
 230                                     sizeof(symlink));
 231                                 if (left_len >= sizeof(left)) {
 232                                         if (m)
 233                                                 free(resolved);
 234                                         errno = ENAMETOOLONG;
 235                                         return (NULL);
 236                                 }
 237                         }
 238                         left_len = strlcpy(left, symlink, sizeof(left));
 239                 }
 240         }
 241
 242         /*
 243          * Remove trailing slash except when the resolved pathname
 244          * is a single "/".
 245          */
 246         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 247                 resolved[resolved_len - 1] = '\0';
 248         return (resolved);
 249 }