lib/libc/stdlib/realpath.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. The names of the authors may not be used to endorse or promote
  15  *    products derived from this software without specific prior written
  16  *    permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  */
  30
  31 #if defined(LIBC_SCCS) && !defined(lint)
  32 static char sccsid[] = "@(#)realpath.c  8.1 (Berkeley) 2/16/94";
  33 #endif /* LIBC_SCCS and not lint */
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "namespace.h"
  38 #include <sys/param.h>
  39 #include <sys/stat.h>
  40
  41 #include <errno.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44 #include <unistd.h>
  45 #include "un-namespace.h"
  46
  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 static char *
  53 realpath1(const char *path, char *resolved)
  54 {
  55         struct stat sb;
  56         char *p, *q;
  57         size_t left_len, resolved_len, next_token_len;
  58         unsigned symlinks;
  59         ssize_t slen;
  60         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  61
  62         symlinks = 0;
  63         if (path[0] == '/') {
  64                 resolved[0] = '/';
  65                 resolved[1] = '\0';
  66                 if (path[1] == '\0')
  67                         return (resolved);
  68                 resolved_len = 1;
  69                 left_len = strlcpy(left, path + 1, sizeof(left));
  70         } else {
  71                 if (getcwd(resolved, PATH_MAX) == NULL) {
  72                         resolved[0] = '.';
  73                         resolved[1] = '\0';
  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
  94                 next_token_len = p != NULL ? p - left : left_len;
  95                 memcpy(next_token, left, next_token_len);
  96                 next_token[next_token_len] = '\0';
  97
  98                 if (p != NULL) {
  99                         left_len -= next_token_len + 1;
 100                         memmove(left, p + 1, left_len + 1);
 101                 } else {
 102                         left[0] = '\0';
 103                         left_len = 0;
 104                 }
 105
 106                 if (resolved[resolved_len - 1] != '/') {
 107                         if (resolved_len + 1 >= PATH_MAX) {
 108                                 errno = ENAMETOOLONG;
 109                                 return (NULL);
 110                         }
 111                         resolved[resolved_len++] = '/';
 112                         resolved[resolved_len] = '\0';
 113                 }
 114                 if (next_token[0] == '\0') {
 115                         /* Handle consequential slashes. */
 116                         continue;
 117                 } else if (strcmp(next_token, ".") == 0) {
 118                         continue;
 119                 } else if (strcmp(next_token, "..") == 0) {
 120                         /*
 121                          * Strip the last path component except when we have
 122                          * single "/"
 123                          */
 124                         if (resolved_len > 1) {
 125                                 resolved[resolved_len - 1] = '\0';
 126                                 q = strrchr(resolved, '/') + 1;
 127                                 *q = '\0';
 128                                 resolved_len = q - resolved;
 129                         }
 130                         continue;
 131                 }
 132
 133                 /*
 134                  * Append the next path component and lstat() it.
 135                  */
 136                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 137                 if (resolved_len >= PATH_MAX) {
 138                         errno = ENAMETOOLONG;
 139                         return (NULL);
 140                 }
 141                 if (lstat(resolved, &sb) != 0)
 142                         return (NULL);
 143                 if (S_ISLNK(sb.st_mode)) {
 144                         if (symlinks++ > MAXSYMLINKS) {
 145                                 errno = ELOOP;
 146                                 return (NULL);
 147                         }
 148                         slen = readlink(resolved, symlink, sizeof(symlink));
 149                         if (slen <= 0 || slen >= sizeof(symlink)) {
 150                                 if (slen < 0)
 151                                         ; /* keep errno from readlink(2) call */
 152                                 else if (slen == 0)
 153                                         errno = ENOENT;
 154                                 else
 155                                         errno = ENAMETOOLONG;
 156                                 return (NULL);
 157                         }
 158                         symlink[slen] = '\0';
 159                         if (symlink[0] == '/') {
 160                                 resolved[1] = 0;
 161                                 resolved_len = 1;
 162                         } else {
 163                                 /* Strip the last path component. */
 164                                 q = strrchr(resolved, '/') + 1;
 165                                 *q = '\0';
 166                                 resolved_len = q - resolved;
 167                         }
 168
 169                         /*
 170                          * If there are any path components left, then
 171                          * append them to symlink. The result is placed
 172                          * in `left'.
 173                          */
 174                         if (p != NULL) {
 175                                 if (symlink[slen - 1] != '/') {
 176                                         if (slen + 1 >= sizeof(symlink)) {
 177                                                 errno = ENAMETOOLONG;
 178                                                 return (NULL);
 179                                         }
 180                                         symlink[slen] = '/';
 181                                         symlink[slen + 1] = 0;
 182                                 }
 183                                 left_len = strlcat(symlink, left,
 184                                     sizeof(symlink));
 185                                 if (left_len >= sizeof(symlink)) {
 186                                         errno = ENAMETOOLONG;
 187                                         return (NULL);
 188                                 }
 189                         }
 190                         left_len = strlcpy(left, symlink, sizeof(left));
 191                 } else if (!S_ISDIR(sb.st_mode) && p != NULL) {
 192                         errno = ENOTDIR;
 193                         return (NULL);
 194                 }
 195         }
 196
 197         /*
 198          * Remove trailing slash except when the resolved pathname
 199          * is a single "/".
 200          */
 201         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 202                 resolved[resolved_len - 1] = '\0';
 203         return (resolved);
 204 }
 205
 206 char *
 207 realpath(const char * __restrict path, char * __restrict resolved)
 208 {
 209         char *m, *res;
 210
 211         if (path == NULL) {
 212                 errno = EINVAL;
 213                 return (NULL);
 214         }
 215         if (path[0] == '\0') {
 216                 errno = ENOENT;
 217                 return (NULL);
 218         }
 219         if (resolved != NULL) {
 220                 m = NULL;
 221         } else {
 222                 m = resolved = malloc(PATH_MAX);
 223                 if (resolved == NULL)
 224                         return (NULL);
 225         }
 226         res = realpath1(path, resolved);
 227         if (res == NULL)
 228                 free(m);
 229         return (res);
 230 }