/*

 * Dropbear - a SSH2 server

 * 

 * Copyright (c) 2002,2003 Matt Johnston

 * All rights reserved.

 * 

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 * 

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE. */

/* Validates a user password */

#include "includes.h"

#include "session.h"

#include "buffer.h"

#include "dbutil.h"

#include "auth.h"

#include "runopts.h"

#if DROPBEAR_SVR_PASSWORD_AUTH

/* not constant time when strings are differing lengths. 

 string content isn't leaked, and crypt hashes are predictable length. */

static int constant_time_strcmp(const char* a, const char* b) {

  size_t la = strlen(a);

  size_t lb = strlen(b);

  if (la != lb) {

    return 1;

  }

  return constant_time_memcmp(a, b, la);

}

/* Process a password auth request, sending success or failure messages as

 * appropriate */

void svr_auth_password(int valid_user) {

  char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */

  char * testcrypt = NULL; /* crypt generated from the user's password sent */

  char * password = NULL;

  unsigned int passwordlen;

  unsigned int changepw;

  /* check if client wants to change password */

  changepw = buf_getbool(ses.payload);

  if (changepw) {

    /* not implemented by this server */

    send_msg_userauth_failure(0, 1);

    return;

  }

  password = buf_getstring(ses.payload, &passwordlen);

  if (valid_user && passwordlen <= DROPBEAR_MAX_PASSWORD_LEN) {

    /* the first bytes of passwdcrypt are the salt */

    passwdcrypt = ses.authstate.pw_passwd;

    testcrypt = crypt(password, passwdcrypt);

  }

  m_burn(password, passwordlen);

  m_free(password);

  /* After we have got the payload contents we can exit if the username

  is invalid. Invalid users have already been logged. */

  if (!valid_user) {

    send_msg_userauth_failure(0, 1);

    return;

  }

  if (passwordlen > DROPBEAR_MAX_PASSWORD_LEN) {

    dropbear_log(LOG_WARNING,

        "Too-long password attempt for '%s' from %s",

        ses.authstate.pw_name,

        svr_ses.addrstring);

    send_msg_userauth_failure(0, 1);

    return;

  }

  if (testcrypt == NULL) {

    /* crypt() with an invalid salt like "!!" */

    dropbear_log(LOG_WARNING, "User account '%s' is locked",

        ses.authstate.pw_name);

    send_msg_userauth_failure(0, 1);

    return;

  }

  /* check for empty password */

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

    dropbear_log(LOG_WARNING, "User '%s' has blank password, rejected",

        ses.authstate.pw_name);

    send_msg_userauth_failure(0, 1);

    return;

  }

  if (constant_time_strcmp(testcrypt, passwdcrypt) == 0) {

    if (svr_opts.multiauthmethod && (ses.authstate.authtypes & ~AUTH_TYPE_PASSWORD)) {

      /* successful password authentication, but extra auth required */

      dropbear_log(LOG_NOTICE,

          "Password auth succeeded for '%s' from %s, extra auth required",

          ses.authstate.pw_name,

          svr_ses.addrstring);

      ses.authstate.authtypes &= ~AUTH_TYPE_PASSWORD; /* password auth ok, delete the method flag */

      send_msg_userauth_failure(1, 0);  /* Send partial success */

    } else {

      /* successful authentication */

      dropbear_log(LOG_NOTICE, 

          "Password auth succeeded for '%s' from %s",

          ses.authstate.pw_name,

          svr_ses.addrstring);

      send_msg_userauth_success();

    }

  } else {

    dropbear_log(LOG_WARNING,

        "Bad password attempt for '%s' from %s",

        ses.authstate.pw_name,

        svr_ses.addrstring);

    send_msg_userauth_failure(0, 1);

  }

}

#endif