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 <fcntl.h>
  46 #include "un-namespace.h"
  47 #include "libc_private.h"
  48
  49 extern int __realpathat(int fd, const char *path, char *buf, size_t size,
  50     int flags);
  51
  52 /*
  53  * Find the real name of path, by removing all ".", ".." and symlink
  54  * components.  Returns (resolved) on success, or (NULL) on failure,
  55  * in which case the path which caused trouble is left in (resolved).
  56  */
  57 static char * __noinline
  58 realpath1(const char *path, char *resolved)
  59 {
  60         struct stat sb;
  61         char *p, *q;
  62         size_t left_len, resolved_len, next_token_len;
  63         unsigned symlinks;
  64         ssize_t slen;
  65         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  66
  67         symlinks = 0;
  68         if (path[0] == '/') {
  69                 resolved[0] = '/';
  70                 resolved[1] = '\0';
  71                 if (path[1] == '\0')
  72                         return (resolved);
  73                 resolved_len = 1;
  74                 left_len = strlcpy(left, path + 1, sizeof(left));
  75         } else {
  76                 if (getcwd(resolved, PATH_MAX) == NULL) {
  77                         resolved[0] = '.';
  78                         resolved[1] = '\0';
  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
  99                 next_token_len = p != NULL ? (size_t)(p - left) : left_len;
 100                 memcpy(next_token, left, next_token_len);
 101                 next_token[next_token_len] = '\0';
 102
 103                 if (p != NULL) {
 104                         left_len -= next_token_len + 1;
 105                         memmove(left, p + 1, left_len + 1);
 106                 } else {
 107                         left[0] = '\0';
 108                         left_len = 0;
 109                 }
 110
 111                 if (resolved[resolved_len - 1] != '/') {
 112                         if (resolved_len + 1 >= PATH_MAX) {
 113                                 errno = ENAMETOOLONG;
 114                                 return (NULL);
 115                         }
 116                         resolved[resolved_len++] = '/';
 117                         resolved[resolved_len] = '\0';
 118                 }
 119                 if (next_token[0] == '\0') {
 120                         /* Handle consequential slashes. */
 121                         continue;
 122                 } else if (strcmp(next_token, ".") == 0) {
 123                         continue;
 124                 } else if (strcmp(next_token, "..") == 0) {
 125                         /*
 126                          * Strip the last path component except when we have
 127                          * single "/"
 128                          */
 129                         if (resolved_len > 1) {
 130                                 resolved[resolved_len - 1] = '\0';
 131                                 q = strrchr(resolved, '/') + 1;
 132                                 *q = '\0';
 133                                 resolved_len = q - resolved;
 134                         }
 135                         continue;
 136                 }
 137
 138                 /*
 139                  * Append the next path component and lstat() it.
 140                  */
 141                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 142                 if (resolved_len >= PATH_MAX) {
 143                         errno = ENAMETOOLONG;
 144                         return (NULL);
 145                 }
 146                 if (lstat(resolved, &sb) != 0)
 147                         return (NULL);
 148                 if (S_ISLNK(sb.st_mode)) {
 149                         if (symlinks++ > MAXSYMLINKS) {
 150                                 errno = ELOOP;
 151                                 return (NULL);
 152                         }
 153                         slen = readlink(resolved, symlink, sizeof(symlink));
 154                         if (slen <= 0 || slen >= (ssize_t)sizeof(symlink)) {
 155                                 if (slen < 0)
 156                                         ; /* keep errno from readlink(2) call */
 157                                 else if (slen == 0)
 158                                         errno = ENOENT;
 159                                 else
 160                                         errno = ENAMETOOLONG;
 161                                 return (NULL);
 162                         }
 163                         symlink[slen] = '\0';
 164                         if (symlink[0] == '/') {
 165                                 resolved[1] = 0;
 166                                 resolved_len = 1;
 167                         } else {
 168                                 /* Strip the last path component. */
 169                                 q = strrchr(resolved, '/') + 1;
 170                                 *q = '\0';
 171                                 resolved_len = q - resolved;
 172                         }
 173
 174                         /*
 175                          * If there are any path components left, then
 176                          * append them to symlink. The result is placed
 177                          * in `left'.
 178                          */
 179                         if (p != NULL) {
 180                                 if (symlink[slen - 1] != '/') {
 181                                         if (slen + 1 >= (ssize_t)sizeof(symlink)) {
 182                                                 errno = ENAMETOOLONG;
 183                                                 return (NULL);
 184                                         }
 185                                         symlink[slen] = '/';
 186                                         symlink[slen + 1] = 0;
 187                                 }
 188                                 left_len = strlcat(symlink, left,
 189                                     sizeof(symlink));
 190                                 if (left_len >= sizeof(symlink)) {
 191                                         errno = ENAMETOOLONG;
 192                                         return (NULL);
 193                                 }
 194                         }
 195                         left_len = strlcpy(left, symlink, sizeof(left));
 196                 } else if (!S_ISDIR(sb.st_mode) && p != NULL) {
 197                         errno = ENOTDIR;
 198                         return (NULL);
 199                 }
 200         }
 201
 202         /*
 203          * Remove trailing slash except when the resolved pathname
 204          * is a single "/".
 205          */
 206         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 207                 resolved[resolved_len - 1] = '\0';
 208         return (resolved);
 209 }
 210
 211 char *
 212 realpath(const char * __restrict path, char * __restrict resolved)
 213 {
 214         char *m, *res;
 215
 216         if (path == NULL) {
 217                 errno = EINVAL;
 218                 return (NULL);
 219         }
 220         if (path[0] == '\0') {
 221                 errno = ENOENT;
 222                 return (NULL);
 223         }
 224         if (resolved != NULL) {
 225                 m = NULL;
 226         } else {
 227                 m = resolved = malloc(PATH_MAX);
 228                 if (resolved == NULL)
 229                         return (NULL);
 230         }
 231         if (__getosreldate() >= 1300080) {
 232                 if (__realpathat(AT_FDCWD, path, resolved, PATH_MAX, 0) == 0)
 233                         return (resolved);
 234         }
 235         res = realpath1(path, resolved);
 236         if (res == NULL)
 237                 free(m);
 238         return (res);
 239 }