sftp-realpath.c

   1 /*      $OpenBSD: sftp-realpath.c,v 1.2 2021/09/02 21:03:54 deraadt 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/stat.h>
  34
  35 #include <errno.h>
  36 #include <stdlib.h>
  37 #include <stddef.h>
  38 #include <string.h>
  39 #include <unistd.h>
  40 #include <limits.h>
  41
  42 #ifndef SYMLOOP_MAX
  43 # define SYMLOOP_MAX 32
  44 #endif
  45
  46 /* XXX rewrite sftp-server to use POSIX realpath and remove this hack */
  47
  48 char *sftp_realpath(const char *path, char *resolved);
  49
  50 /*
  51  * char *realpath(const char *path, char resolved[PATH_MAX]);
  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 char *
  58 sftp_realpath(const char *path, char *resolved)
  59 {
  60         struct stat sb;
  61         char *p, *q, *s;
  62         size_t left_len, resolved_len;
  63         unsigned symlinks;
  64         int serrno, slen, mem_allocated;
  65         char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
  66
  67         if (path[0] == '\0') {
  68                 errno = ENOENT;
  69                 return (NULL);
  70         }
  71
  72         serrno = errno;
  73
  74         if (resolved == NULL) {
  75                 resolved = malloc(PATH_MAX);
  76                 if (resolved == NULL)
  77                         return (NULL);
  78                 mem_allocated = 1;
  79         } else
  80                 mem_allocated = 0;
  81
  82         symlinks = 0;
  83         if (path[0] == '/') {
  84                 resolved[0] = '/';
  85                 resolved[1] = '\0';
  86                 if (path[1] == '\0')
  87                         return (resolved);
  88                 resolved_len = 1;
  89                 left_len = strlcpy(left, path + 1, sizeof(left));
  90         } else {
  91                 if (getcwd(resolved, PATH_MAX) == NULL) {
  92                         if (mem_allocated)
  93                                 free(resolved);
  94                         else
  95                                 strlcpy(resolved, ".", PATH_MAX);
  96                         return (NULL);
  97                 }
  98                 resolved_len = strlen(resolved);
  99                 left_len = strlcpy(left, path, sizeof(left));
 100         }
 101         if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
 102                 errno = ENAMETOOLONG;
 103                 goto err;
 104         }
 105
 106         /*
 107          * Iterate over path components in `left'.
 108          */
 109         while (left_len != 0) {
 110                 /*
 111                  * Extract the next path component and adjust `left'
 112                  * and its length.
 113                  */
 114                 p = strchr(left, '/');
 115                 s = p ? p : left + left_len;
 116                 if (s - left >= (ptrdiff_t)sizeof(next_token)) {
 117                         errno = ENAMETOOLONG;
 118                         goto err;
 119                 }
 120                 memcpy(next_token, left, s - left);
 121                 next_token[s - left] = '\0';
 122                 left_len -= s - left;
 123                 if (p != NULL)
 124                         memmove(left, s + 1, left_len + 1);
 125                 if (resolved[resolved_len - 1] != '/') {
 126                         if (resolved_len + 1 >= PATH_MAX) {
 127                                 errno = ENAMETOOLONG;
 128                                 goto err;
 129                         }
 130                         resolved[resolved_len++] = '/';
 131                         resolved[resolved_len] = '\0';
 132                 }
 133                 if (next_token[0] == '\0')
 134                         continue;
 135                 else if (strcmp(next_token, ".") == 0)
 136                         continue;
 137                 else if (strcmp(next_token, "..") == 0) {
 138                         /*
 139                          * Strip the last path component except when we have
 140                          * single "/"
 141                          */
 142                         if (resolved_len > 1) {
 143                                 resolved[resolved_len - 1] = '\0';
 144                                 q = strrchr(resolved, '/') + 1;
 145                                 *q = '\0';
 146                                 resolved_len = q - resolved;
 147                         }
 148                         continue;
 149                 }
 150
 151                 /*
 152                  * Append the next path component and lstat() it. If
 153                  * lstat() fails we still can return successfully if
 154                  * there are no more path components left.
 155                  */
 156                 resolved_len = strlcat(resolved, next_token, PATH_MAX);
 157                 if (resolved_len >= PATH_MAX) {
 158                         errno = ENAMETOOLONG;
 159                         goto err;
 160                 }
 161                 if (lstat(resolved, &sb) != 0) {
 162                         if (errno == ENOENT && p == NULL) {
 163                                 errno = serrno;
 164                                 return (resolved);
 165                         }
 166                         goto err;
 167                 }
 168                 if (S_ISLNK(sb.st_mode)) {
 169                         if (symlinks++ > SYMLOOP_MAX) {
 170                                 errno = ELOOP;
 171                                 goto err;
 172                         }
 173                         slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 174                         if (slen < 0)
 175                                 goto err;
 176                         symlink[slen] = '\0';
 177                         if (symlink[0] == '/') {
 178                                 resolved[1] = 0;
 179                                 resolved_len = 1;
 180                         } else if (resolved_len > 1) {
 181                                 /* Strip the last path component. */
 182                                 resolved[resolved_len - 1] = '\0';
 183                                 q = strrchr(resolved, '/') + 1;
 184                                 *q = '\0';
 185                                 resolved_len = q - resolved;
 186                         }
 187
 188                         /*
 189                          * If there are any path components left, then
 190                          * append them to symlink. The result is placed
 191                          * in `left'.
 192                          */
 193                         if (p != NULL) {
 194                                 if (symlink[slen - 1] != '/') {
 195                                         if (slen + 1 >=
 196                                             (ptrdiff_t)sizeof(symlink)) {
 197                                                 errno = ENAMETOOLONG;
 198                                                 goto err;
 199                                         }
 200                                         symlink[slen] = '/';
 201                                         symlink[slen + 1] = 0;
 202                                 }
 203                                 left_len = strlcat(symlink, left, sizeof(symlink));
 204                                 if (left_len >= sizeof(symlink)) {
 205                                         errno = ENAMETOOLONG;
 206                                         goto err;
 207                                 }
 208                         }
 209                         left_len = strlcpy(left, symlink, sizeof(left));
 210                 }
 211         }
 212
 213         /*
 214          * Remove trailing slash except when the resolved pathname
 215          * is a single "/".
 216          */
 217         if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
 218                 resolved[resolved_len - 1] = '\0';
 219         return (resolved);
 220
 221 err:
 222         if (mem_allocated)
 223                 free(resolved);
 224         return (NULL);
 225 }