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 1.20 2003/05/28 08:23:01 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 == NULL) {
  63                 errno = EINVAL;
  64                 return (NULL);
  65         }
  66         if (path[0] == '\0') {
  67                 errno = ENOENT;
  68                 return (NULL);
  69         } else if (path[0] == '/') {
  70                 resolved[0] = '/';
  71                 resolved[1] = '\0';
  72                 if (path[1] == '\0')
  73                         return (resolved);
  74                 resolved_len = 1;
  75                 left_len = strlcpy(left, path + 1, sizeof(left));
  76         } else {
  77                 if (getcwd(resolved, PATH_MAX) == NULL) {
  78                         strlcpy(resolved, ".", PATH_MAX);
  79                         return (NULL);
  80                 }
  81                 resolved_len = strlen(resolved);
  82                 left_len = strlcpy(left, path, sizeof(left));
  83         }
  84         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  85                 errno = ENAMETOOLONG;
  86                 return (NULL);
  87         }
  88
  89         /*
  90          * Iterate over path components in `left'.
  91          */
  92         while (left_len != 0) {
  93                 /*
  94                  * Extract the next path component and adjust `left'
  95                  * and its length.
  96                  */
  97                 p = strchr(left, '/');
  98                 s = p ? p : left + left_len;
  99                 if (s >= left + sizeof(next_token)) {
 100                         errno = ENAMETOOLONG;
 101                         return (NULL);
 102                 }
 103                 memcpy(next_token, left, s - left);
 104                 next_token[s - left] = '\0';
 105                 left_len -= s - left;
 106                 if (p != NULL)
 107                         memmove(left, s + 1, left_len + 1);
 108                 if (resolved[resolved_len - 1] != '/') {
 109                         if (resolved_len + 1 >= PATH_MAX) {
 110                                 errno = ENAMETOOLONG;
 111                                 return (NULL);
 112                         }
 113                         resolved[resolved_len++] = '/';
 114                         resolved[resolved_len] = '\0';
 115                 }
 116                 if (next_token[0] == '\0')
 117                         continue;
 118                 else if (strcmp(next_token, ".") == 0)
 119                         continue;
 120                 else if (strcmp(next_token, "..") == 0) {
 121                         /*
 122                          * Strip the last path component except when we have
 123                          * single "/"
 124                          */
 125                         if (resolved_len > 1) {
 126                                 resolved[resolved_len - 1] = '\0';
 127                                 q = strrchr(resolved, '/') + 1;
 128                                 *q = '\0';
 129                                 resolved_len = q - resolved;
 130                         }
 131                         continue;
 132                 }
 133
 134                 /*
 135                  * Append the next path component and lstat() it. If
 136                  * lstat() fails we still can return successfully if
 137                  * there are no more path components left.
 138                  */
 139                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 140                 if (resolved_len >= PATH_MAX) {
 141                         errno = ENAMETOOLONG;
 142                         return (NULL);
 143                 }
 144                 if (lstat(resolved, &sb) != 0) {
 145                         if (errno == ENOENT && p == NULL) {
 146                                 errno = serrno;
 147                                 return (resolved);
 148                         }
 149                         return (NULL);
 150                 }
 151                 if (S_ISLNK(sb.st_mode)) {
 152                         if (symlinks++ > MAXSYMLINKS) {
 153                                 errno = ELOOP;
 154                                 return (NULL);
 155                         }
 156                         slen = readlink(resolved, my_symlink, sizeof(my_symlink) - 1);
 157                         if (slen < 0)
 158                                 return (NULL);
 159                         my_symlink[slen] = '\0';
 160                         if (my_symlink[0] == '/') {
 161                                 resolved[1] = 0;
 162                                 resolved_len = 1;
 163                         } else if (resolved_len > 1) {
 164                                 /* Strip the last path component. */
 165                                 resolved[resolved_len - 1] = '\0';
 166                                 q = strrchr(resolved, '/') + 1;
 167                                 *q = '\0';
 168                                 resolved_len = q - resolved;
 169                         }
 170
 171                         /*
 172                          * If there are any path components left, then
 173                          * append them to symlink. The result is placed
 174                          * in `left'.
 175                          */
 176                         if (p != NULL) {
 177                                 if (my_symlink[slen - 1] != '/') {
 178                                         if (slen + 1 >= (int)sizeof(my_symlink)) {
 179                                                 errno = ENAMETOOLONG;
 180                                                 return (NULL);
 181                                         }
 182                                         my_symlink[slen] = '/';
 183                                         my_symlink[slen + 1] = 0;
 184                                 }
 185                                 left_len = strlcat(my_symlink, left, sizeof(left));
 186                                 if (left_len >= sizeof(left)) {
 187                                         errno = ENAMETOOLONG;
 188                                         return (NULL);
 189                                 }
 190                         }
 191                         left_len = strlcpy(left, my_symlink, sizeof(left));
 192                 }
 193         }
 194
 195         /*
 196          * Remove trailing slash except when the resolved pathname
 197          * is a single "/".
 198          */
 199         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 200                 resolved[resolved_len - 1] = '\0';
 201         return (resolved);
 202 }