/*  $OpenBSD: sftp-realpath.c,v 1.2 2021/09/02 21:03:54 deraadt Exp $ */

/*

 * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. The names of the authors may not be used to endorse or promote

 *    products derived from this software without specific prior written

 *    permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

#include "includes.h"

#include <sys/types.h>

#include <sys/stat.h>

#include <errno.h>

#include <stdlib.h>

#include <stddef.h>

#include <string.h>

#include <unistd.h>

#include <limits.h>

#ifndef SYMLOOP_MAX

# define SYMLOOP_MAX 32

#endif

/* XXX rewrite sftp-server to use POSIX realpath and remove this hack */

char *sftp_realpath(const char *path, char *resolved);

/*

 * char *realpath(const char *path, char resolved[PATH_MAX]);

 *

 * Find the real name of path, by removing all ".", ".." and symlink

 * components.  Returns (resolved) on success, or (NULL) on failure,

 * in which case the path which caused trouble is left in (resolved).

 */

char *

sftp_realpath(const char *path, char *resolved)

{

  struct stat sb;

  char *p, *q, *s;

  size_t left_len, resolved_len;

  unsigned symlinks;

  int serrno, slen, mem_allocated;

  char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];

  if (path[0] == '\0') {

    errno = ENOENT;

    return (NULL);

  }

  serrno = errno;

  if (resolved == NULL) {

    resolved = malloc(PATH_MAX);

    if (resolved == NULL)

      return (NULL);

    mem_allocated = 1;

  } else

    mem_allocated = 0;

  symlinks = 0;

  if (path[0] == '/') {

    resolved[0] = '/';

    resolved[1] = '\0';

    if (path[1] == '\0')

      return (resolved);

    resolved_len = 1;

    left_len = strlcpy(left, path + 1, sizeof(left));

  } else {

    if (getcwd(resolved, PATH_MAX) == NULL) {

      if (mem_allocated)

        free(resolved);

      else

        strlcpy(resolved, ".", PATH_MAX);

      return (NULL);

    }

    resolved_len = strlen(resolved);

    left_len = strlcpy(left, path, sizeof(left));

  }

  if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {

    errno = ENAMETOOLONG;

    goto err;

  }

  /*

   * Iterate over path components in `left'.

   */

  while (left_len != 0) {

    /*

     * Extract the next path component and adjust `left'

     * and its length.

     */

    p = strchr(left, '/');

    s = p ? p : left + left_len;

    if (s - left >= (ptrdiff_t)sizeof(next_token)) {

      errno = ENAMETOOLONG;

      goto err;

    }

    memcpy(next_token, left, s - left);

    next_token[s - left] = '\0';

    left_len -= s - left;

    if (p != NULL)

      memmove(left, s + 1, left_len + 1);

    if (resolved[resolved_len - 1] != '/') {

      if (resolved_len + 1 >= PATH_MAX) {

        errno = ENAMETOOLONG;

        goto err;

      }

      resolved[resolved_len++] = '/';

      resolved[resolved_len] = '\0';

    }

    if (next_token[0] == '\0')

      continue;

    else if (strcmp(next_token, ".") == 0)

      continue;

    else if (strcmp(next_token, "..") == 0) {

      /*

       * Strip the last path component except when we have

       * single "/"

       */

      if (resolved_len > 1) {

        resolved[resolved_len - 1] = '\0';

        q = strrchr(resolved, '/') + 1;

        *q = '\0';

        resolved_len = q - resolved;

      }

      continue;

    }

    /*

     * Append the next path component and lstat() it. If

     * lstat() fails we still can return successfully if

     * there are no more path components left.

     */

    resolved_len = strlcat(resolved, next_token, PATH_MAX);

    if (resolved_len >= PATH_MAX) {

      errno = ENAMETOOLONG;

      goto err;

    }

    if (lstat(resolved, &sb) != 0) {

      if (errno == ENOENT && p == NULL) {

        errno = serrno;

        return (resolved);

      }

      goto err;

    }

    if (S_ISLNK(sb.st_mode)) {

      if (symlinks++ > SYMLOOP_MAX) {

        errno = ELOOP;

        goto err;

      }

      slen = readlink(resolved, symlink, sizeof(symlink) - 1);

      if (slen < 0)

        goto err;

      symlink[slen] = '\0';

      if (symlink[0] == '/') {

        resolved[1] = 0;

        resolved_len = 1;

      } else if (resolved_len > 1) {

        /* Strip the last path component. */

        resolved[resolved_len - 1] = '\0';

        q = strrchr(resolved, '/') + 1;

        *q = '\0';

        resolved_len = q - resolved;

      }

      /*

       * If there are any path components left, then

       * append them to symlink. The result is placed

       * in `left'.

       */

      if (p != NULL) {

        if (symlink[slen - 1] != '/') {

          if (slen + 1 >=

              (ptrdiff_t)sizeof(symlink)) {

            errno = ENAMETOOLONG;

            goto err;

          }

          symlink[slen] = '/';

          symlink[slen + 1] = 0;

        }

        left_len = strlcat(symlink, left, sizeof(symlink));

        if (left_len >= sizeof(symlink)) {

          errno = ENAMETOOLONG;

          goto err;

        }

      }

      left_len = strlcpy(left, symlink, sizeof(left));

    }

  }

  /*

   * Remove trailing slash except when the resolved pathname

   * is a single "/".

   */

  if (resolved_len > 1 && resolved[resolved_len - 1] == '/')

    resolved[resolved_len - 1] = '\0';

  return (resolved);

err:

  if (mem_allocated)

    free(resolved);

  return (NULL);

}