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  * char *realpath(const char *path, char resolved[PATH_MAX]);
  47  *
  48  * Find the real name of path, by removing all ".", ".." and symlink
  49  * components.  Returns (resolved) on success, or (NULL) on failure,
  50  * in which case the path which caused trouble is left in (resolved).
  51  */
  52 char *
  53 realpath(const char *path, char resolved[PATH_MAX])
  54 {
  55         struct stat sb;
  56         char *p, *q, *s;
  57         size_t left_len, resolved_len;
  58         unsigned symlinks;
  59         int serrno, slen;
  60         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  61
  62         serrno = errno;
  63         symlinks = 0;
  64         if (path[0] == '/') {
  65                 resolved[0] = '/';
  66                 resolved[1] = '\0';
  67                 if (path[1] == '\0')
  68                         return (resolved);
  69                 resolved_len = 1;
  70                 left_len = strlcpy(left, path + 1, sizeof(left));
  71         } else {
  72                 if (getcwd(resolved, PATH_MAX) == NULL) {
  73                         strlcpy(resolved, ".", PATH_MAX);
  74                         return (NULL);
  75                 }
  76                 resolved_len = strlen(resolved);
  77                 left_len = strlcpy(left, path, sizeof(left));
  78         }
  79         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  80                 errno = ENAMETOOLONG;
  81                 return (NULL);
  82         }
  83
  84         /*
  85          * Iterate over path components in `left'.
  86          */
  87         while (left_len != 0) {
  88                 /*
  89                  * Extract the next path component and adjust `left'
  90                  * and its length.
  91                  */
  92                 p = strchr(left, '/');
  93                 s = p ? p : left + left_len;
  94                 if (s - left >= sizeof(next_token)) {
  95                         errno = ENAMETOOLONG;
  96                         return (NULL);
  97                 }
  98                 memcpy(next_token, left, s - left);
  99                 next_token[s - left] = '\0';
 100                 left_len -= s - left;
 101                 if (p != NULL)
 102                         memmove(left, s + 1, left_len + 1);
 103                 if (resolved[resolved_len - 1] != '/') {
 104                         if (resolved_len + 1 >= PATH_MAX) {
 105                                 errno = ENAMETOOLONG;
 106                                 return (NULL);
 107                         }
 108                         resolved[resolved_len++] = '/';
 109                         resolved[resolved_len] = '\0';
 110                 }
 111                 if (next_token[0] == '\0')
 112                         continue;
 113                 else if (strcmp(next_token, ".") == 0)
 114                         continue;
 115                 else if (strcmp(next_token, "..") == 0) {
 116                         /*
 117                          * Strip the last path component except when we have
 118                          * single "/"
 119                          */
 120                         if (resolved_len > 1) {
 121                                 resolved[resolved_len - 1] = '\0';
 122                                 q = strrchr(resolved, '/') + 1;
 123                                 *q = '\0';
 124                                 resolved_len = q - resolved;
 125                         }
 126                         continue;
 127                 }
 128
 129                 /*
 130                  * Append the next path component and lstat() it. If
 131                  * lstat() fails we still can return successfully if
 132                  * there are no more path components left.
 133                  */
 134                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 135                 if (resolved_len >= PATH_MAX) {
 136                         errno = ENAMETOOLONG;
 137                         return (NULL);
 138                 }
 139                 if (lstat(resolved, &sb) != 0) {
 140                         if (errno == ENOENT && p == NULL) {
 141                                 errno = serrno;
 142                                 return (resolved);
 143                         }
 144                         return (NULL);
 145                 }
 146                 if (S_ISLNK(sb.st_mode)) {
 147                         if (symlinks++ > MAXSYMLINKS) {
 148                                 errno = ELOOP;
 149                                 return (NULL);
 150                         }
 151                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 152                         if (slen < 0)
 153                                 return (NULL);
 154                         symlink[slen] = '\0';
 155                         if (symlink[0] == '/') {
 156                                 resolved[1] = 0;
 157                                 resolved_len = 1;
 158                         } else if (resolved_len > 1) {
 159                                 /* Strip the last path component. */
 160                                 resolved[resolved_len - 1] = '\0';
 161                                 q = strrchr(resolved, '/') + 1;
 162                                 *q = '\0';
 163                                 resolved_len = q - resolved;
 164                         }
 165
 166                         /*
 167                          * If there are any path components left, then
 168                          * append them to symlink. The result is placed
 169                          * in `left'.
 170                          */
 171                         if (p != NULL) {
 172                                 if (symlink[slen - 1] != '/') {
 173                                         if (slen + 1 >= sizeof(symlink)) {
 174                                                 errno = ENAMETOOLONG;
 175                                                 return (NULL);
 176                                         }
 177                                         symlink[slen] = '/';
 178                                         symlink[slen + 1] = 0;
 179                                 }
 180                                 left_len = strlcat(symlink, left, sizeof(left));
 181                                 if (left_len >= sizeof(left)) {
 182                                         errno = ENAMETOOLONG;
 183                                         return (NULL);
 184                                 }
 185                         }
 186                         left_len = strlcpy(left, symlink, sizeof(left));
 187                 }
 188         }
 189
 190         /*
 191          * Remove trailing slash except when the resolved pathname
 192          * is a single "/".
 193          */
 194         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 195                 resolved[resolved_len - 1] = '\0';
 196         return (resolved);
 197 }