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  * @(#)realpath.c       8.1 (Berkeley) 2/16/94
  29  * $FreeBSD: src/lib/libc/stdlib/realpath.c,v 1.9.2.2 2003/06/02 13:31:16 fjoe Exp $
  30  * $DragonFly: src/lib/libc/stdlib/realpath.c,v 1.2 2003/06/17 04:26:46 dillon Exp $
  31  */
  32
  33 #include <sys/param.h>
  34 #include <sys/stat.h>
  35
  36 #include <errno.h>
  37 #include <stdlib.h>
  38 #include <string.h>
  39 #include <unistd.h>
  40
  41 /*
  42  * char *realpath(const char *path, char resolved[PATH_MAX]);
  43  *
  44  * Find the real name of path, by removing all ".", ".." and symlink
  45  * components.  Returns (resolved) on success, or (NULL) on failure,
  46  * in which case the path which caused trouble is left in (resolved).
  47  */
  48 char *
  49 realpath(const char *path, char resolved[PATH_MAX])
  50 {
  51         struct stat sb;
  52         char *p, *q, *s;
  53         size_t left_len, resolved_len;
  54         unsigned symlinks;
  55         int serrno, slen;
  56         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  57
  58         serrno = errno;
  59         symlinks = 0;
  60         if (path[0] == '/') {
  61                 resolved[0] = '/';
  62                 resolved[1] = '\0';
  63                 if (path[1] == '\0')
  64                         return (resolved);
  65                 resolved_len = 1;
  66                 left_len = strlcpy(left, path + 1, sizeof(left));
  67         } else {
  68                 if (getcwd(resolved, PATH_MAX) == NULL) {
  69                         strlcpy(resolved, ".", PATH_MAX);
  70                         return (NULL);
  71                 }
  72                 resolved_len = strlen(resolved);
  73                 left_len = strlcpy(left, path, sizeof(left));
  74         }
  75         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  76                 errno = ENAMETOOLONG;
  77                 return (NULL);
  78         }
  79
  80         /*
  81          * Iterate over path components in `left'.
  82          */
  83         while (left_len != 0) {
  84                 /*
  85                  * Extract the next path component and adjust `left'
  86                  * and its length.
  87                  */
  88                 p = strchr(left, '/');
  89                 s = p ? p : left + left_len;
  90                 if (s - left >= sizeof(next_token)) {
  91                         errno = ENAMETOOLONG;
  92                         return (NULL);
  93                 }
  94                 memcpy(next_token, left, s - left);
  95                 next_token[s - left] = '\0';
  96                 left_len -= s - left;
  97                 if (p != NULL)
  98                         memmove(left, s + 1, left_len + 1);
  99                 if (resolved[resolved_len - 1] != '/') {
 100                         if (resolved_len + 1 >= PATH_MAX) {
 101                                 errno = ENAMETOOLONG;
 102                                 return (NULL);
 103                         }
 104                         resolved[resolved_len++] = '/';
 105                         resolved[resolved_len] = '\0';
 106                 }
 107                 if (next_token[0] == '\0')
 108                         continue;
 109                 else if (strcmp(next_token, ".") == 0)
 110                         continue;
 111                 else if (strcmp(next_token, "..") == 0) {
 112                         /*
 113                          * Strip the last path component except when we have
 114                          * single "/"
 115                          */
 116                         if (resolved_len > 1) {
 117                                 resolved[resolved_len - 1] = '\0';
 118                                 q = strrchr(resolved, '/') + 1;
 119                                 *q = '\0';
 120                                 resolved_len = q - resolved;
 121                         }
 122                         continue;
 123                 }
 124
 125                 /*
 126                  * Append the next path component and lstat() it. If
 127                  * lstat() fails we still can return successfully if
 128                  * there are no more path components left.
 129                  */
 130                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 131                 if (resolved_len >= PATH_MAX) {
 132                         errno = ENAMETOOLONG;
 133                         return (NULL);
 134                 }
 135                 if (lstat(resolved, &sb) != 0) {
 136                         if (errno == ENOENT && p == NULL) {
 137                                 errno = serrno;
 138                                 return (resolved);
 139                         }
 140                         return (NULL);
 141                 }
 142                 if (S_ISLNK(sb.st_mode)) {
 143                         if (symlinks++ > MAXSYMLINKS) {
 144                                 errno = ELOOP;
 145                                 return (NULL);
 146                         }
 147                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 148                         if (slen < 0)
 149                                 return (NULL);
 150                         symlink[slen] = '\0';
 151                         if (symlink[0] == '/') {
 152                                 resolved[1] = 0;
 153                                 resolved_len = 1;
 154                         } else if (resolved_len > 1) {
 155                                 /* Strip the last path component. */
 156                                 resolved[resolved_len - 1] = '\0';
 157                                 q = strrchr(resolved, '/') + 1;
 158                                 *q = '\0';
 159                                 resolved_len = q - resolved;
 160                         }
 161
 162                         /*
 163                          * If there are any path components left, then
 164                          * append them to symlink. The result is placed
 165                          * in `left'.
 166                          */
 167                         if (p != NULL) {
 168                                 if (symlink[slen - 1] != '/') {
 169                                         if (slen + 1 >= sizeof(symlink)) {
 170                                                 errno = ENAMETOOLONG;
 171                                                 return (NULL);
 172                                         }
 173                                         symlink[slen] = '/';
 174                                         symlink[slen + 1] = 0;
 175                                 }
 176                                 left_len = strlcat(symlink, left, sizeof(left));
 177                                 if (left_len >= sizeof(left)) {
 178                                         errno = ENAMETOOLONG;
 179                                         return (NULL);
 180                                 }
 181                         }
 182                         left_len = strlcpy(left, symlink, sizeof(left));
 183                 }
 184         }
 185
 186         /*
 187          * Remove trailing slash except when the resolved pathname
 188          * is a single "/".
 189          */
 190         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 191                 resolved[resolved_len - 1] = '\0';
 192         return (resolved);
 193 }