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  * $FreeBSD: src/lib/libc/stdlib/realpath.c SVN 227090 2011/11/04 ed $
  29  */
  30
  31 #include "namespace.h"
  32 #include <sys/param.h>
  33 #include <sys/stat.h>
  34
  35 #include <errno.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <unistd.h>
  39 #include "un-namespace.h"
  40
  41 /*
  42  * Find the real name of path, by removing all ".", ".." and symlink
  43  * components.  Returns (resolved) on success, or (NULL) on failure,
  44  * in which case the path which caused trouble is left in (resolved).
  45  */
  46 char *
  47 realpath(const char * __restrict path, char * __restrict resolved)
  48 {
  49         struct stat sb;
  50         char *p, *q, *s;
  51         size_t left_len, resolved_len;
  52         unsigned symlinks;
  53         int m, serrno, slen;
  54         char left[PATH_MAX], next_token[PATH_MAX], my_symlink[PATH_MAX];
  55
  56         if (path == NULL) {
  57                 errno = EINVAL;
  58                 return (NULL);
  59         }
  60         if (path[0] == '\0') {
  61                 errno = ENOENT;
  62                 return (NULL);
  63         }
  64         serrno = errno;
  65         if (resolved == NULL) {
  66                 resolved = malloc(PATH_MAX);
  67                 if (resolved == NULL)
  68                         return (NULL);
  69                 m = 1;
  70         } else
  71                 m = 0;
  72         symlinks = 0;
  73         if (path[0] == '/') {
  74                 resolved[0] = '/';
  75                 resolved[1] = '\0';
  76                 if (path[1] == '\0')
  77                         return (resolved);
  78                 resolved_len = 1;
  79                 left_len = strlcpy(left, path + 1, sizeof(left));
  80         } else {
  81                 if (getcwd(resolved, PATH_MAX) == NULL) {
  82                         if (m)
  83                                 free(resolved);
  84                         else {
  85                                 resolved[0] = '.';
  86                                 resolved[1] = '\0';
  87                         }
  88                         return (NULL);
  89                 }
  90                 resolved_len = strlen(resolved);
  91                 left_len = strlcpy(left, path, sizeof(left));
  92         }
  93         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  94                 if (m)
  95                         free(resolved);
  96                 errno = ENAMETOOLONG;
  97                 return (NULL);
  98         }
  99
 100         /*
 101          * Iterate over path components in `left'.
 102          */
 103         while (left_len != 0) {
 104                 /*
 105                  * Extract the next path component and adjust `left'
 106                  * and its length.
 107                  */
 108                 p = strchr(left, '/');
 109                 s = p ? p : left + left_len;
 110                 if (s - left >= sizeof(next_token)) {
 111                         if (m)
 112                                 free(resolved);
 113                         errno = ENAMETOOLONG;
 114                         return (NULL);
 115                 }
 116                 memcpy(next_token, left, s - left);
 117                 next_token[s - left] = '\0';
 118                 left_len -= s - left;
 119                 if (p != NULL)
 120                         memmove(left, s + 1, left_len + 1);
 121                 if (resolved[resolved_len - 1] != '/') {
 122                         if (resolved_len + 1 >= PATH_MAX) {
 123                                 if (m)
 124                                         free(resolved);
 125                                 errno = ENAMETOOLONG;
 126                                 return (NULL);
 127                         }
 128                         resolved[resolved_len++] = '/';
 129                         resolved[resolved_len] = '\0';
 130                 }
 131                 if (next_token[0] == '\0')
 132                         continue;
 133                 else if (strcmp(next_token, ".") == 0)
 134                         continue;
 135                 else if (strcmp(next_token, "..") == 0) {
 136                         /*
 137                          * Strip the last path component except when we have
 138                          * single "/"
 139                          */
 140                         if (resolved_len > 1) {
 141                                 resolved[resolved_len - 1] = '\0';
 142                                 q = strrchr(resolved, '/') + 1;
 143                                 *q = '\0';
 144                                 resolved_len = q - resolved;
 145                         }
 146                         continue;
 147                 }
 148
 149                 /*
 150                  * Append the next path component and lstat() it. If
 151                  * lstat() fails we still can return successfully if
 152                  * there are no more path components left.
 153                  */
 154                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 155                 if (resolved_len >= PATH_MAX) {
 156                         if (m)
 157                                 free(resolved);
 158                         errno = ENAMETOOLONG;
 159                         return (NULL);
 160                 }
 161                 if (lstat(resolved, &sb) != 0) {
 162                         if (errno == ENOENT && p == NULL) {
 163                                 errno = serrno;
 164                                 return (resolved);
 165                         }
 166                         if (m)
 167                                 free(resolved);
 168                         return (NULL);
 169                 }
 170                 if (S_ISLNK(sb.st_mode)) {
 171                         if (symlinks++ > MAXSYMLINKS) {
 172                                 if (m)
 173                                         free(resolved);
 174                                 errno = ELOOP;
 175                                 return (NULL);
 176                         }
 177                         slen = readlink(resolved, my_symlink, sizeof(my_symlink) - 1);
 178                         if (slen < 0) {
 179                                 if (m)
 180                                         free(resolved);
 181                                 return (NULL);
 182                         }
 183                         my_symlink[slen] = '\0';
 184                         if (my_symlink[0] == '/') {
 185                                 resolved[1] = 0;
 186                                 resolved_len = 1;
 187                         } else if (resolved_len > 1) {
 188                                 /* Strip the last path component. */
 189                                 resolved[resolved_len - 1] = '\0';
 190                                 q = strrchr(resolved, '/') + 1;
 191                                 *q = '\0';
 192                                 resolved_len = q - resolved;
 193                         }
 194
 195                         /*
 196                          * If there are any path components left, then
 197                          * append them to symlink. The result is placed
 198                          * in `left'.
 199                          */
 200                         if (p != NULL) {
 201                                 if (my_symlink[slen - 1] != '/') {
 202                                         if (slen + 1 >= (int)sizeof(my_symlink)) {
 203                                                 if (m)
 204                                                         free(resolved);
 205                                                 errno = ENAMETOOLONG;
 206                                                 return (NULL);
 207                                         }
 208                                         my_symlink[slen] = '/';
 209                                         my_symlink[slen + 1] = 0;
 210                                 }
 211                                 left_len = strlcat(my_symlink, left,
 212                                     sizeof(my_symlink));
 213                                 if (left_len >= sizeof(left)) {
 214                                         if (m)
 215                                                 free(resolved);
 216                                         errno = ENAMETOOLONG;
 217                                         return (NULL);
 218                                 }
 219                         }
 220                         left_len = strlcpy(left, my_symlink, sizeof(left));
 221                 }
 222         }
 223
 224         /*
 225          * Remove trailing slash except when the resolved pathname
 226          * is a single "/".
 227          */
 228         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 229                 resolved[resolved_len - 1] = '\0';
 230         return (resolved);
 231 }