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 #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 <fcntl.h>
  40 #include "un-namespace.h"
  41 #include "libc_private.h"
  42
  43 extern int __realpathat(int fd, const char *path, char *buf, size_t size,
  44     int flags);
  45
  46 /*
  47  * Find the real name of path, by removing all ".", ".." and symlink
  48  * components.  Returns (resolved) on success, or (NULL) on failure,
  49  * in which case the path which caused trouble is left in (resolved).
  50  */
  51 static char * __noinline
  52 realpath1(const char *path, char *resolved)
  53 {
  54         struct stat sb;
  55         char *p, *q;
  56         size_t left_len, resolved_len, next_token_len;
  57         unsigned symlinks;
  58         ssize_t slen;
  59         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  60
  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                         resolved[0] = '.';
  72                         resolved[1] = '\0';
  73                         return (NULL);
  74                 }
  75                 resolved_len = strlen(resolved);
  76                 left_len = strlcpy(left, path, sizeof(left));
  77         }
  78         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
  79                 errno = ENAMETOOLONG;
  80                 return (NULL);
  81         }
  82
  83         /*
  84          * Iterate over path components in `left'.
  85          */
  86         while (left_len != 0) {
  87                 /*
  88                  * Extract the next path component and adjust `left'
  89                  * and its length.
  90                  */
  91                 p = strchr(left, '/');
  92
  93                 next_token_len = p != NULL ? (size_t)(p - left) : left_len;
  94                 memcpy(next_token, left, next_token_len);
  95                 next_token[next_token_len] = '\0';
  96
  97                 if (p != NULL) {
  98                         left_len -= next_token_len + 1;
  99                         memmove(left, p + 1, left_len + 1);
 100                 } else {
 101                         left[0] = '\0';
 102                         left_len = 0;
 103                 }
 104
 105                 if (resolved[resolved_len - 1] != '/') {
 106                         if (resolved_len + 1 >= PATH_MAX) {
 107                                 errno = ENAMETOOLONG;
 108                                 return (NULL);
 109                         }
 110                         resolved[resolved_len++] = '/';
 111                         resolved[resolved_len] = '\0';
 112                 }
 113                 if (next_token[0] == '\0') {
 114                         /* Handle consequential slashes. */
 115                         continue;
 116                 } else if (strcmp(next_token, ".") == 0) {
 117                         continue;
 118                 } else if (strcmp(next_token, "..") == 0) {
 119                         /*
 120                          * Strip the last path component except when we have
 121                          * single "/"
 122                          */
 123                         if (resolved_len > 1) {
 124                                 resolved[resolved_len - 1] = '\0';
 125                                 q = strrchr(resolved, '/') + 1;
 126                                 *q = '\0';
 127                                 resolved_len = q - resolved;
 128                         }
 129                         continue;
 130                 }
 131
 132                 /*
 133                  * Append the next path component and lstat() it.
 134                  */
 135                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 136                 if (resolved_len >= PATH_MAX) {
 137                         errno = ENAMETOOLONG;
 138                         return (NULL);
 139                 }
 140                 if (lstat(resolved, &sb) != 0)
 141                         return (NULL);
 142                 if (S_ISLNK(sb.st_mode)) {
 143                         if (symlinks++ > MAXSYMLINKS) {
 144                                 errno = ELOOP;
 145                                 return (NULL);
 146                         }
 147                         slen = readlink(resolved, symlink, sizeof(symlink));
 148                         if (slen <= 0 || slen >= (ssize_t)sizeof(symlink)) {
 149                                 if (slen < 0)
 150                                         ; /* keep errno from readlink(2) call */
 151                                 else if (slen == 0)
 152                                         errno = ENOENT;
 153                                 else
 154                                         errno = ENAMETOOLONG;
 155                                 return (NULL);
 156                         }
 157                         symlink[slen] = '\0';
 158                         if (symlink[0] == '/') {
 159                                 resolved[1] = 0;
 160                                 resolved_len = 1;
 161                         } else {
 162                                 /* Strip the last path component. */
 163                                 q = strrchr(resolved, '/') + 1;
 164                                 *q = '\0';
 165                                 resolved_len = q - resolved;
 166                         }
 167
 168                         /*
 169                          * If there are any path components left, then
 170                          * append them to symlink. The result is placed
 171                          * in `left'.
 172                          */
 173                         if (p != NULL) {
 174                                 if (symlink[slen - 1] != '/') {
 175                                         if (slen + 1 >= (ssize_t)sizeof(symlink)) {
 176                                                 errno = ENAMETOOLONG;
 177                                                 return (NULL);
 178                                         }
 179                                         symlink[slen] = '/';
 180                                         symlink[slen + 1] = 0;
 181                                 }
 182                                 left_len = strlcat(symlink, left,
 183                                     sizeof(symlink));
 184                                 if (left_len >= sizeof(symlink)) {
 185                                         errno = ENAMETOOLONG;
 186                                         return (NULL);
 187                                 }
 188                         }
 189                         left_len = strlcpy(left, symlink, sizeof(left));
 190                 } else if (!S_ISDIR(sb.st_mode) && p != NULL) {
 191                         errno = ENOTDIR;
 192                         return (NULL);
 193                 }
 194         }
 195
 196         /*
 197          * Remove trailing slash except when the resolved pathname
 198          * is a single "/".
 199          */
 200         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 201                 resolved[resolved_len - 1] = '\0';
 202         return (resolved);
 203 }
 204
 205 char *
 206 realpath(const char * __restrict path, char * __restrict resolved)
 207 {
 208         char *m, *res;
 209
 210         if (path == NULL) {
 211                 errno = EINVAL;
 212                 return (NULL);
 213         }
 214         if (path[0] == '\0') {
 215                 errno = ENOENT;
 216                 return (NULL);
 217         }
 218         if (resolved != NULL) {
 219                 m = NULL;
 220         } else {
 221                 m = resolved = malloc(PATH_MAX);
 222                 if (resolved == NULL)
 223                         return (NULL);
 224         }
 225         if (__getosreldate() >= 1300080) {
 226                 if (__realpathat(AT_FDCWD, path, resolved, PATH_MAX, 0) == 0)
 227                         return (resolved);
 228         }
 229         res = realpath1(path, resolved);
 230         if (res == NULL)
 231                 free(m);
 232         return (res);
 233 }