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 1.4 2005/04/28 13:47:15 joerg Exp $
  31  */
  32
  33 #include "namespace.h"
  34 #include <sys/param.h>
  35 #include <sys/stat.h>
  36
  37 #include <errno.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40 #include <unistd.h>
  41 #include "un-namespace.h"
  42
  43 /*
  44  * char *realpath(const char *path, char resolved[PATH_MAX]);
  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 *path, char resolved[PATH_MAX])
  52 {
  53         struct stat sb;
  54         char *p, *q, *s;
  55         size_t left_len, resolved_len;
  56         unsigned symlinks;
  57         int serrno, slen;
  58         char left[PATH_MAX], next_token[PATH_MAX], my_symlink[PATH_MAX];
  59
  60         serrno = errno;
  61         symlinks = 0;
  62         if (path[0] == '/') {
  63                 resolved[0] = '/';
  64                 resolved[1] = '\0';
  65                 if (path[1] == '\0')
  66                         return (resolved);
  67                 resolved_len = 1;
  68                 left_len = strlcpy(left, path + 1, sizeof(left));
  69         } else {
  70                 if (getcwd(resolved, PATH_MAX) == NULL) {
  71                         strlcpy(resolved, ".", PATH_MAX);
  72                         return (NULL);
  73                 }
  74                 resolved_len = strlen(resolved);
  75                 left_len = strlcpy(left, path, sizeof(left));
  76         }
  77         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  78                 errno = ENAMETOOLONG;
  79                 return (NULL);
  80         }
  81
  82         /*
  83          * Iterate over path components in `left'.
  84          */
  85         while (left_len != 0) {
  86                 /*
  87                  * Extract the next path component and adjust `left'
  88                  * and its length.
  89                  */
  90                 p = strchr(left, '/');
  91                 s = p ? p : left + left_len;
  92                 if (s >= left + sizeof(next_token)) {
  93                         errno = ENAMETOOLONG;
  94                         return (NULL);
  95                 }
  96                 memcpy(next_token, left, s - left);
  97                 next_token[s - left] = '\0';
  98                 left_len -= s - left;
  99                 if (p != NULL)
 100                         memmove(left, s + 1, left_len + 1);
 101                 if (resolved[resolved_len - 1] != '/') {
 102                         if (resolved_len + 1 >= PATH_MAX) {
 103                                 errno = ENAMETOOLONG;
 104                                 return (NULL);
 105                         }
 106                         resolved[resolved_len++] = '/';
 107                         resolved[resolved_len] = '\0';
 108                 }
 109                 if (next_token[0] == '\0')
 110                         continue;
 111                 else if (strcmp(next_token, ".") == 0)
 112                         continue;
 113                 else if (strcmp(next_token, "..") == 0) {
 114                         /*
 115                          * Strip the last path component except when we have
 116                          * single "/"
 117                          */
 118                         if (resolved_len > 1) {
 119                                 resolved[resolved_len - 1] = '\0';
 120                                 q = strrchr(resolved, '/') + 1;
 121                                 *q = '\0';
 122                                 resolved_len = q - resolved;
 123                         }
 124                         continue;
 125                 }
 126
 127                 /*
 128                  * Append the next path component and lstat() it. If
 129                  * lstat() fails we still can return successfully if
 130                  * there are no more path components left.
 131                  */
 132                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 133                 if (resolved_len >= PATH_MAX) {
 134                         errno = ENAMETOOLONG;
 135                         return (NULL);
 136                 }
 137                 if (lstat(resolved, &sb) != 0) {
 138                         if (errno == ENOENT && p == NULL) {
 139                                 errno = serrno;
 140                                 return (resolved);
 141                         }
 142                         return (NULL);
 143                 }
 144                 if (S_ISLNK(sb.st_mode)) {
 145                         if (symlinks++ > MAXSYMLINKS) {
 146                                 errno = ELOOP;
 147                                 return (NULL);
 148                         }
 149                         slen = readlink(resolved, my_symlink, sizeof(my_symlink) - 1);
 150                         if (slen < 0)
 151                                 return (NULL);
 152                         my_symlink[slen] = '\0';
 153                         if (my_symlink[0] == '/') {
 154                                 resolved[1] = 0;
 155                                 resolved_len = 1;
 156                         } else if (resolved_len > 1) {
 157                                 /* Strip the last path component. */
 158                                 resolved[resolved_len - 1] = '\0';
 159                                 q = strrchr(resolved, '/') + 1;
 160                                 *q = '\0';
 161                                 resolved_len = q - resolved;
 162                         }
 163
 164                         /*
 165                          * If there are any path components left, then
 166                          * append them to symlink. The result is placed
 167                          * in `left'.
 168                          */
 169                         if (p != NULL) {
 170                                 if (my_symlink[slen - 1] != '/') {
 171                                         if (slen + 1 >= (int)sizeof(my_symlink)) {
 172                                                 errno = ENAMETOOLONG;
 173                                                 return (NULL);
 174                                         }
 175                                         my_symlink[slen] = '/';
 176                                         my_symlink[slen + 1] = 0;
 177                                 }
 178                                 left_len = strlcat(my_symlink, left, sizeof(left));
 179                                 if (left_len >= sizeof(left)) {
 180                                         errno = ENAMETOOLONG;
 181                                         return (NULL);
 182                                 }
 183                         }
 184                         left_len = strlcpy(left, my_symlink, sizeof(left));
 185                 }
 186         }
 187
 188         /*
 189          * Remove trailing slash except when the resolved pathname
 190          * is a single "/".
 191          */
 192         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 193                 resolved[resolved_len - 1] = '\0';
 194         return (resolved);
 195 }