crypto/openssh/sftp-realpath.c

   1 /*      $OpenBSD: sftp-realpath.c,v 1.1 2019/07/05 04:55:40 djm Exp $ */
   2 /*
   3  * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. The names of the authors may not be used to endorse or promote
  14  *    products derived from this software without specific prior written
  15  *    permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 #include "includes.h"
  31
  32 #include <sys/types.h>
  33 #include <sys/param.h>
  34 #include <sys/stat.h>
  35
  36 #include <errno.h>
  37 #include <stdlib.h>
  38 #include <stddef.h>
  39 #include <string.h>
  40 #include <unistd.h>
  41 #include <limits.h>
  42
  43 #ifndef SYMLOOP_MAX
  44 # define SYMLOOP_MAX 32
  45 #endif
  46
  47 /* XXX rewrite sftp-server to use POSIX realpath and remove this hack */
  48
  49 char *sftp_realpath(const char *path, char *resolved);
  50
  51 /*
  52  * char *realpath(const char *path, char resolved[PATH_MAX]);
  53  *
  54  * Find the real name of path, by removing all ".", ".." and symlink
  55  * components.  Returns (resolved) on success, or (NULL) on failure,
  56  * in which case the path which caused trouble is left in (resolved).
  57  */
  58 char *
  59 sftp_realpath(const char *path, char *resolved)
  60 {
  61         struct stat sb;
  62         char *p, *q, *s;
  63         size_t left_len, resolved_len;
  64         unsigned symlinks;
  65         int serrno, slen, mem_allocated;
  66         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  67
  68         if (path[0] == '\0') {
  69                 errno = ENOENT;
  70                 return (NULL);
  71         }
  72
  73         serrno = errno;
  74
  75         if (resolved == NULL) {
  76                 resolved = malloc(PATH_MAX);
  77                 if (resolved == NULL)
  78                         return (NULL);
  79                 mem_allocated = 1;
  80         } else
  81                 mem_allocated = 0;
  82
  83         symlinks = 0;
  84         if (path[0] == '/') {
  85                 resolved[0] = '/';
  86                 resolved[1] = '\0';
  87                 if (path[1] == '\0')
  88                         return (resolved);
  89                 resolved_len = 1;
  90                 left_len = strlcpy(left, path + 1, sizeof(left));
  91         } else {
  92                 if (getcwd(resolved, PATH_MAX) == NULL) {
  93                         if (mem_allocated)
  94                                 free(resolved);
  95                         else
  96                                 strlcpy(resolved, ".", PATH_MAX);
  97                         return (NULL);
  98                 }
  99                 resolved_len = strlen(resolved);
 100                 left_len = strlcpy(left, path, sizeof(left));
 101         }
 102         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
 103                 errno = ENAMETOOLONG;
 104                 goto err;
 105         }
 106
 107         /*
 108          * Iterate over path components in `left'.
 109          */
 110         while (left_len != 0) {
 111                 /*
 112                  * Extract the next path component and adjust `left'
 113                  * and its length.
 114                  */
 115                 p = strchr(left, '/');
 116                 s = p ? p : left + left_len;
 117                 if (s - left >= (ptrdiff_t)sizeof(next_token)) {
 118                         errno = ENAMETOOLONG;
 119                         goto err;
 120                 }
 121                 memcpy(next_token, left, s - left);
 122                 next_token[s - left] = '\0';
 123                 left_len -= s - left;
 124                 if (p != NULL)
 125                         memmove(left, s + 1, left_len + 1);
 126                 if (resolved[resolved_len - 1] != '/') {
 127                         if (resolved_len + 1 >= PATH_MAX) {
 128                                 errno = ENAMETOOLONG;
 129                                 goto err;
 130                         }
 131                         resolved[resolved_len++] = '/';
 132                         resolved[resolved_len] = '\0';
 133                 }
 134                 if (next_token[0] == '\0')
 135                         continue;
 136                 else if (strcmp(next_token, ".") == 0)
 137                         continue;
 138                 else if (strcmp(next_token, "..") == 0) {
 139                         /*
 140                          * Strip the last path component except when we have
 141                          * single "/"
 142                          */
 143                         if (resolved_len > 1) {
 144                                 resolved[resolved_len - 1] = '\0';
 145                                 q = strrchr(resolved, '/') + 1;
 146                                 *q = '\0';
 147                                 resolved_len = q - resolved;
 148                         }
 149                         continue;
 150                 }
 151
 152                 /*
 153                  * Append the next path component and lstat() it. If
 154                  * lstat() fails we still can return successfully if
 155                  * there are no more path components left.
 156                  */
 157                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 158                 if (resolved_len >= PATH_MAX) {
 159                         errno = ENAMETOOLONG;
 160                         goto err;
 161                 }
 162                 if (lstat(resolved, &sb) != 0) {
 163                         if (errno == ENOENT && p == NULL) {
 164                                 errno = serrno;
 165                                 return (resolved);
 166                         }
 167                         goto err;
 168                 }
 169                 if (S_ISLNK(sb.st_mode)) {
 170                         if (symlinks++ > SYMLOOP_MAX) {
 171                                 errno = ELOOP;
 172                                 goto err;
 173                         }
 174                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 175                         if (slen < 0)
 176                                 goto err;
 177                         symlink[slen] = '\0';
 178                         if (symlink[0] == '/') {
 179                                 resolved[1] = 0;
 180                                 resolved_len = 1;
 181                         } else if (resolved_len > 1) {
 182                                 /* Strip the last path component. */
 183                                 resolved[resolved_len - 1] = '\0';
 184                                 q = strrchr(resolved, '/') + 1;
 185                                 *q = '\0';
 186                                 resolved_len = q - resolved;
 187                         }
 188
 189                         /*
 190                          * If there are any path components left, then
 191                          * append them to symlink. The result is placed
 192                          * in `left'.
 193                          */
 194                         if (p != NULL) {
 195                                 if (symlink[slen - 1] != '/') {
 196                                         if (slen + 1 >=
 197                                             (ptrdiff_t)sizeof(symlink)) {
 198                                                 errno = ENAMETOOLONG;
 199                                                 goto err;
 200                                         }
 201                                         symlink[slen] = '/';
 202                                         symlink[slen + 1] = 0;
 203                                 }
 204                                 left_len = strlcat(symlink, left, sizeof(symlink));
 205                                 if (left_len >= sizeof(symlink)) {
 206                                         errno = ENAMETOOLONG;
 207                                         goto err;
 208                                 }
 209                         }
 210                         left_len = strlcpy(left, symlink, sizeof(left));
 211                 }
 212         }
 213
 214         /*
 215          * Remove trailing slash except when the resolved pathname
 216          * is a single "/".
 217          */
 218         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 219                 resolved[resolved_len - 1] = '\0';
 220         return (resolved);
 221
 222 err:
 223         if (mem_allocated)
 224                 free(resolved);
 225         return (NULL);
 226 }