niceSOFT/libssh | Gitverse

src/packet.c
2 026 строк67 KB
Jakub Jelen
CVE-2023-1667:packet: Do not allow servers to initiate handshake
04 май 2023, 12:52
04 май 2023, 12:52247a4a7
/*
 * packet.c - packet building functions
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2003-2013 by Aris Adamantiadis
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

#ifndef _WIN32
#include <netinet/in.h>
#include <arpa/inet.h>
#endif

#include "libssh/priv.h"
#include "libssh/ssh2.h"
#include "libssh/crypto.h"
#include "libssh/buffer.h"
#include "libssh/packet.h"
#include "libssh/socket.h"
#include "libssh/channels.h"
#include "libssh/misc.h"
#include "libssh/session.h"
#include "libssh/messages.h"
#include "libssh/pcap.h"
#include "libssh/kex.h"
#include "libssh/auth.h"
#include "libssh/gssapi.h"
#include "libssh/bytearray.h"
#include "libssh/dh.h"

static ssh_packet_callback default_packet_handlers[]= {
  ssh_packet_disconnect_callback,          // SSH2_MSG_DISCONNECT                 1
  ssh_packet_ignore_callback,              // SSH2_MSG_IGNORE	                    2
  ssh_packet_unimplemented,                // SSH2_MSG_UNIMPLEMENTED              3
  ssh_packet_ignore_callback,              // SSH2_MSG_DEBUG	                    4
#if WITH_SERVER
  ssh_packet_service_request,              // SSH2_MSG_SERVICE_REQUEST	          5
#else
  NULL,
#endif
  ssh_packet_service_accept,               // SSH2_MSG_SERVICE_ACCEPT             6
  ssh_packet_ext_info,                     // SSH2_MSG_EXT_INFO                   7
  NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL,      //                                     8-19
  ssh_packet_kexinit,                      // SSH2_MSG_KEXINIT	                  20
  ssh_packet_newkeys,                      // SSH2_MSG_NEWKEYS                    21
  NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL,                                    //                                     22-29
#if WITH_SERVER
  ssh_packet_kexdh_init,                   // SSH2_MSG_KEXDH_INIT                 30
                                           // SSH2_MSG_KEX_DH_GEX_REQUEST_OLD     30
#else
  NULL,
#endif
  NULL,                                    // SSH2_MSG_KEXDH_REPLY                31
                                           // SSH2_MSG_KEX_DH_GEX_GROUP           31
  NULL,                                    // SSH2_MSG_KEX_DH_GEX_INIT            32
  NULL,                                    // SSH2_MSG_KEX_DH_GEX_REPLY           33
  NULL,                                    // SSH2_MSG_KEX_DH_GEX_REQUEST         34
  NULL, NULL, NULL, NULL, NULL, NULL,	NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL,                                    //                                     35-49
#if WITH_SERVER
  ssh_packet_userauth_request,             // SSH2_MSG_USERAUTH_REQUEST           50
#else
  NULL,
#endif
  ssh_packet_userauth_failure,             // SSH2_MSG_USERAUTH_FAILURE           51
  ssh_packet_userauth_success,             // SSH2_MSG_USERAUTH_SUCCESS           52
  ssh_packet_userauth_banner,              // SSH2_MSG_USERAUTH_BANNER            53
  NULL,NULL,NULL,NULL,NULL,NULL,           //                                     54-59
  ssh_packet_userauth_pk_ok,               // SSH2_MSG_USERAUTH_PK_OK             60
                                           // SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ  60
                                           // SSH2_MSG_USERAUTH_INFO_REQUEST	  60
                                           // SSH2_MSG_USERAUTH_GSSAPI_RESPONSE   60
  ssh_packet_userauth_info_response,       // SSH2_MSG_USERAUTH_INFO_RESPONSE     61
                                           // SSH2_MSG_USERAUTH_GSSAPI_TOKEN      61
  NULL,                                    //                                     62
  NULL,                             // SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE 63
  NULL,                                    // SSH2_MSG_USERAUTH_GSSAPI_ERROR      64
  NULL,                                    // SSH2_MSG_USERAUTH_GSSAPI_ERRTOK     65
#if defined(WITH_GSSAPI) && defined(WITH_SERVER)
  ssh_packet_userauth_gssapi_mic,          // SSH2_MSG_USERAUTH_GSSAPI_MIC        66
#else /* WITH_GSSAPI && WITH_SERVER */
  NULL,
#endif /* WITH_GSSAPI && WITH_SERVER */
  NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL,                  //                                     67-79
#ifdef WITH_SERVER
  ssh_packet_global_request,               // SSH2_MSG_GLOBAL_REQUEST             80
#else /* WITH_SERVER */
  NULL,
#endif /* WITH_SERVER */
  ssh_request_success,                     // SSH2_MSG_REQUEST_SUCCESS            81
  ssh_request_denied,                      // SSH2_MSG_REQUEST_FAILURE            82
  NULL, NULL, NULL, NULL, NULL, NULL, NULL,//                                     83-89
  ssh_packet_channel_open,                 // SSH2_MSG_CHANNEL_OPEN               90
  ssh_packet_channel_open_conf,            // SSH2_MSG_CHANNEL_OPEN_CONFIRMATION  91
  ssh_packet_channel_open_fail,            // SSH2_MSG_CHANNEL_OPEN_FAILURE       92
  channel_rcv_change_window,               // SSH2_MSG_CHANNEL_WINDOW_ADJUST      93
  channel_rcv_data,                        // SSH2_MSG_CHANNEL_DATA               94
  channel_rcv_data,                        // SSH2_MSG_CHANNEL_EXTENDED_DATA      95
  channel_rcv_eof,                         // SSH2_MSG_CHANNEL_EOF	              96
  channel_rcv_close,                       // SSH2_MSG_CHANNEL_CLOSE              97
  channel_rcv_request,                     // SSH2_MSG_CHANNEL_REQUEST            98
  ssh_packet_channel_success,              // SSH2_MSG_CHANNEL_SUCCESS            99
  ssh_packet_channel_failure,              // SSH2_MSG_CHANNEL_FAILURE            100
};

/** @internal
 * @brief check if the received packet is allowed for the current session state
 * @param session current ssh_session
 * @returns SSH_PACKET_ALLOWED if the packet is allowed; SSH_PACKET_DENIED
 * if the packet arrived in wrong state; SSH_PACKET_UNKNOWN if the packet type
 * is unknown
 */
static enum ssh_packet_filter_result_e ssh_packet_incoming_filter(ssh_session session)
{
    enum ssh_packet_filter_result_e rc;

#ifdef DEBUG_PACKET
    SSH_LOG(SSH_LOG_PACKET, "Filtering packet type %d",
            session->in_packet.type);
#endif

    switch(session->in_packet.type) {
    case SSH2_MSG_DISCONNECT:                         // 1
        /*
         * States required:
         * - None
         *
         * Transitions:
         * - session->socket->state = SSH_SOCKET_CLOSED
         * - session->session_state = SSH_SESSION_STATE_ERROR
         * */

        /* Always allowed */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_IGNORE:                             // 2
        /*
         * States required:
         * - None
         *
         * Transitions:
         * - None
         * */

        /* Always allowed */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_UNIMPLEMENTED:                      // 3
        /*
         * States required:
         * - None
         *
         * Transitions:
         * - None
         * */

        /* Always allowed */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_DEBUG:                              // 4
        /*
         * States required:
         * - None
         *
         * Transitions:
         * - None
         * */

        /* Always allowed */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_SERVICE_REQUEST:                    // 5
        /* Server only */

        /*
         * States required:
         * - session->session_state == SSH_SESSION_STATE_AUTHENTICATING
         *   or session->session_state == SSH_SESSION_STATE_AUTHENTICATED
         * - session->dh_handshake_state == DH_STATE_FINISHED
         *
         * Transitions:
         * - None
         * */

        /* If this is a client, reject the message */
        if (session->client) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if ((session->session_state != SSH_SESSION_STATE_AUTHENTICATING) &&
            (session->session_state != SSH_SESSION_STATE_AUTHENTICATED))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_SERVICE_ACCEPT:                     // 6
        /*
         * States required:
         * - session->session_state == SSH_SESSION_STATE_AUTHENTICATING
         *   or session->session_state == SSH_SESSION_STATE_AUTHENTICATED
         * - session->dh_handshake_state == DH_STATE_FINISHED
         * - session->auth.service_state == SSH_AUTH_SERVICE_SENT
         *
         * Transitions:
         * - auth.service_state = SSH_AUTH_SERVICE_ACCEPTED
         * */

        if ((session->session_state != SSH_SESSION_STATE_AUTHENTICATING) &&
            (session->session_state != SSH_SESSION_STATE_AUTHENTICATED))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        /* TODO check if only auth service can be requested */
        if (session->auth.service_state != SSH_AUTH_SERVICE_SENT) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_EXT_INFO:                           // 7
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         *   or session->session_state == SSH_SESSION_STATE_AUTHENTICATED
         *   (re-exchange)
         * - dh_handshake_state == DH_STATE_FINISHED
         *
         * Transitions:
         * - None
         * */

        if ((session->session_state != SSH_SESSION_STATE_AUTHENTICATING) &&
            (session->session_state != SSH_SESSION_STATE_AUTHENTICATED))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEXINIT:                            // 20
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *   or session_state == SSH_SESSION_STATE_INITIAL_KEX
         * - dh_handshake_state == DH_STATE_INIT
         *   or dh_handshake_state == DH_STATE_INIT_SENT (re-exchange)
         *   or dh_handshake_state == DH_STATE_FINISHED (re-exchange)
         *
         * Transitions:
         * - session->dh_handshake_state = DH_STATE_INIT
         * - session->session_state = SSH_SESSION_STATE_KEXINIT_RECEIVED
         *
         * On server:
         * - session->session_state = SSH_SESSION_STATE_DH
         * */

        if ((session->session_state != SSH_SESSION_STATE_AUTHENTICATED) &&
            (session->session_state != SSH_SESSION_STATE_INITIAL_KEX))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if ((session->dh_handshake_state != DH_STATE_INIT) &&
            (session->dh_handshake_state != DH_STATE_INIT_SENT) &&
            (session->dh_handshake_state != DH_STATE_FINISHED))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_NEWKEYS:                            // 21
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_DH
         * - dh_handshake_state == DH_STATE_NEWKEYS_SENT
         *
         * Transitions:
         * - session->dh_handshake_state = DH_STATE_FINISHED
         * - session->session_state = SSH_SESSION_STATE_AUTHENTICATING
         * if session->flags & SSH_SESSION_FLAG_AUTHENTICATED
         * - session->session_state = SSH_SESSION_STATE_AUTHENTICATED
         * */

        /* If DH has not been started, reject message */
        if (session->session_state != SSH_SESSION_STATE_DH) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        /* Only allowed if dh_handshake_state is in NEWKEYS_SENT state */
        if (session->dh_handshake_state != DH_STATE_NEWKEYS_SENT) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEXDH_INIT:                         // 30
      // SSH2_MSG_KEX_ECDH_INIT:                      // 30
      // SSH2_MSG_ECMQV_INIT:                         // 30
      // SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:             // 30

        /* Server only */

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_DH
         * - dh_handshake_state == DH_STATE_INIT
         *
         * Transitions:
         * - session->dh_handshake_state = DH_STATE_INIT_SENT
         * then calls dh_handshake_server which triggers:
         * - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT
         * */

        if (!session->server) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->session_state != SSH_SESSION_STATE_DH) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        /* Only allowed if dh_handshake_state is in initial state */
        if (session->dh_handshake_state != DH_STATE_INIT) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEXDH_REPLY:                        // 31
      // SSH2_MSG_KEX_ECDH_REPLY:                     // 31
      // SSH2_MSG_ECMQV_REPLY:                        // 31
      // SSH2_MSG_KEX_DH_GEX_GROUP:                   // 31

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_DH
         * - dh_handshake_state == DH_STATE_INIT_SENT
         *   or dh_handshake_state == DH_STATE_REQUEST_SENT (dh-gex)
         *
         * Transitions:
         * - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT
         * */

        if (session->session_state != SSH_SESSION_STATE_DH) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_INIT_SENT &&
            session->dh_handshake_state != DH_STATE_REQUEST_SENT) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEX_DH_GEX_INIT:                    // 32
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEX_DH_GEX_REPLY:                   // 33
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_KEX_DH_GEX_REQUEST:                 // 34
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_REQUEST:                   // 50
        /* Server only */

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - dh_handshake_state == DH_STATE_FINISHED
         *
         * Transitions:
         * - if authentication was successful:
         *   - session_state = SSH_SESSION_STATE_AUTHENTICATED
         * */

        /* If this is a client, reject the message */
        if (session->client) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_FAILURE:                   // 51
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - dh_handshake_state == DH_STATE_FINISHED
         * - session->auth.state == SSH_AUTH_STATE_KBDINT_SENT
         *   or session->auth.state == SSH_AUTH_STATE_PUBKEY_OFFER_SENT
         *   or session->auth.state == SSH_AUTH_STATE_PUBKEY_AUTH_SENT
         *   or session->auth.state == SSH_AUTH_STATE_PASSWORD_AUTH_SENT
         *   or session->auth.state == SSH_AUTH_STATE_GSSAPI_MIC_SENT
         *
         * Transitions:
         * - if unpacking failed:
         *   - session->auth.state = SSH_AUTH_ERROR
         * - if failure was partial:
         *   - session->auth.state = SSH_AUTH_PARTIAL
         * - else:
         *   - session->auth.state = SSH_AUTH_STATE_FAILED
         * */

        /* If this is a server, reject the message */
        if (session->server) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_SUCCESS:                   // 52
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - dh_handshake_state == DH_STATE_FINISHED
         * - session->auth.state == SSH_AUTH_STATE_KBDINT_SENT
         *   or session->auth.state == SSH_AUTH_STATE_PUBKEY_AUTH_SENT
         *   or session->auth.state == SSH_AUTH_STATE_PASSWORD_AUTH_SENT
         *   or session->auth.state == SSH_AUTH_STATE_GSSAPI_MIC_SENT
         *   or session->auth.state == SSH_AUTH_STATE_AUTH_NONE_SENT
         *
         * Transitions:
         * - session->auth.state = SSH_AUTH_STATE_SUCCESS
         * - session->session_state = SSH_SESSION_STATE_AUTHENTICATED
         * - session->flags |= SSH_SESSION_FLAG_AUTHENTICATED
         * - sessions->auth.current_method = SSH_AUTH_METHOD_UNKNOWN
         * */

        /* If this is a server, reject the message */
        if (session->server) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if ((session->auth.state != SSH_AUTH_STATE_KBDINT_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_PUBKEY_AUTH_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_PASSWORD_AUTH_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_GSSAPI_MIC_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_AUTH_NONE_SENT))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_BANNER:                    // 53
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_PK_OK:                     // 60
      // SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ:          // 60
      // SSH2_MSG_USERAUTH_INFO_REQUEST:              // 60
      // SSH2_MSG_USERAUTH_GSSAPI_RESPONSE:           // 60

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - session->auth.state == SSH_AUTH_STATE_KBDINT_SENT
         *   or
         *   session->auth.state == SSH_AUTH_STATE_GSSAPI_REQUEST_SENT
         *   or
         *   session->auth.state == SSH_AUTH_STATE_PUBKEY_OFFER_SENT
         *
         * Transitions:
         * Depending on the current state, the message is treated
         * differently:
         * - session->auth.state == SSH_AUTH_STATE_KBDINT_SENT
         *   - session->auth.state = SSH_AUTH_STATE_INFO
         * - session->auth.state == SSH_AUTH_STATE_GSSAPI_REQUEST_SENT
         *   - session->auth.state = SSH_AUTH_STATE_GSSAPI_TOKEN
         * - session->auth.state == SSH_AUTH_STATE_PUBKEY_OFFER_SENT
         *   - session->auth.state = SSH_AUTH_STATE_PK_OK
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if ((session->auth.state != SSH_AUTH_STATE_KBDINT_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_PUBKEY_OFFER_SENT) &&
            (session->auth.state != SSH_AUTH_STATE_GSSAPI_REQUEST_SENT))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_INFO_RESPONSE:             // 61
      // SSH2_MSG_USERAUTH_GSSAPI_TOKEN:              // 61

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - session_state->auth.state == SSH_SESSION_STATE_GSSAPI_TOKEN
         *   or
         *   session_state->auth.state == SSH_SESSION_STATE_INFO
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if ((session->auth.state != SSH_AUTH_STATE_INFO) &&
            (session->auth.state != SSH_AUTH_STATE_GSSAPI_TOKEN))
        {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE:  // 63
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_GSSAPI_ERROR:              // 64
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_GSSAPI_ERRTOK:             // 65
        /* TODO Not filtered */
        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_USERAUTH_GSSAPI_MIC:                // 66
        /* Server only */

        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATING
         * - session->gssapi->state == SSH_GSSAPI_STATE_RCV_MIC
         *
         * Transitions:
         * Depending on the result of the verification, the states are
         * changed:
         * - SSH_AUTH_SUCCESS:
         *   - session->session_state = SSH_SESSION_STATE_AUTHENTICATED
         *   - session->flags != SSH_SESSION_FLAG_AUTHENTICATED
         * - SSH_AUTH_PARTIAL:
         *   - None
         * - any other case:
         *   - None
         * */

        /* If this is a client, reject the message */
        if (session->client) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->dh_handshake_state != DH_STATE_FINISHED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATING) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_GLOBAL_REQUEST:                     // 80
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_REQUEST_SUCCESS:                    // 81
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - From channel->request_state == SSH_CHANNEL_REQ_STATE_PENDING
         * - To   channel->request_state = SSH_CHANNEL_REQ_STATE_ACCEPTED
         *
         * If not in a pending state, message is ignored in the callback handler.
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_REQUEST_FAILURE:                    // 82
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - From channel->request_state == SSH_CHANNEL_REQ_STATE_PENDING
         * - To   channel->request_state = SSH_CHANNEL_REQ_STATE_ACCEPTED
         *
         * If not in a pending state, message is ignored in the callback handler.
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_OPEN:                       // 90
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:          // 91
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - channel->state = SSH_CHANNEL_STATE_OPEN
         * - channel->flags &= ~SSH_CHANNEL_FLAG_NOT_BOUND
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_OPEN_FAILURE:               // 92
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - channel->state = SSH_CHANNEL_STATE_OPEN_DENIED
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_WINDOW_ADJUST:              // 93
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_DATA:                       // 94
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_EXTENDED_DATA:              // 95
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_EOF:                        // 96
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - None
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_CLOSE:                      // 97
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - channel->state = SSH_CHANNEL_STATE_CLOSED
         * - channel->flags |= SSH_CHANNEL_FLAG_CLOSED_REMOTE
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_REQUEST:                    // 98
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - Depends on the request
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_SUCCESS:                    // 99
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - From channel->request_state == SSH_CHANNEL_REQ_STATE_PENDING
         * - To   channel->request_state = SSH_CHANNEL_REQ_STATE_ACCEPTED
         *
         * If not in a pending state, message is ignored in the callback handler.
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    case SSH2_MSG_CHANNEL_FAILURE:                    // 100
        /*
         * States required:
         * - session_state == SSH_SESSION_STATE_AUTHENTICATED
         *
         * Transitions:
         * - From channel->request_state == SSH_CHANNEL_REQ_STATE_PENDING
         * - To   channel->request_state = SSH_CHANNEL_REQ_STATE_ACCEPTED
         *
         * If not in a pending state, message is ignored in the callback handler.
         * */

        if (session->session_state != SSH_SESSION_STATE_AUTHENTICATED) {
            rc = SSH_PACKET_DENIED;
            break;
        }

        rc = SSH_PACKET_ALLOWED;
        break;
    default:
        /* Unknown message, do not filter */
        rc = SSH_PACKET_UNKNOWN;
        goto end;
    }

end:
#ifdef DEBUG_PACKET
    if (rc == SSH_PACKET_DENIED) {
        SSH_LOG(SSH_LOG_PACKET, "REJECTED packet type %d: ",
                session->in_packet.type);
    }

    if (rc == SSH_PACKET_UNKNOWN) {
        SSH_LOG(SSH_LOG_PACKET, "UNKNOWN packet type %d",
                session->in_packet.type);
    }
#endif

    return rc;
}

/* Returns current_crypto structure from the session.
 * During key exchange (or rekey), after one of the sides
 * sending NEWKEYS packet, this might return next_crypto for one
 * of the directions that is ahead to send already queued packets
 */
struct ssh_crypto_struct *
ssh_packet_get_current_crypto(ssh_session session,
                              enum ssh_crypto_direction_e direction)
{
    struct ssh_crypto_struct *crypto = NULL;

    if (session == NULL) {
        return NULL;
    }

    if (session->current_crypto != NULL &&
        session->current_crypto->used & direction) {
        crypto = session->current_crypto;
    } else if (session->next_crypto != NULL &&
               session->next_crypto->used & direction) {
        crypto = session->next_crypto;
    } else {
        return NULL;
    }

    switch (direction) {
    case SSH_DIRECTION_IN:
        if (crypto->in_cipher != NULL) {
            return crypto;
        }
        break;
    case SSH_DIRECTION_OUT:
        if (crypto->out_cipher != NULL) {
            return crypto;
        }
        break;
    case SSH_DIRECTION_BOTH:
        if (crypto->in_cipher != NULL &&
            crypto->out_cipher != NULL) {
            return crypto;
        }
    }

    return NULL;
}

#define MAX_PACKETS    (1UL<<31)

static bool ssh_packet_need_rekey(ssh_session session,
                                  const uint32_t payloadsize)
{
    bool data_rekey_needed = false;
    struct ssh_crypto_struct *crypto = NULL;
    struct ssh_cipher_struct *out_cipher = NULL, *in_cipher = NULL;
    uint32_t next_blocks;

    /* We can safely rekey only in authenticated state */
    if ((session->flags & SSH_SESSION_FLAG_AUTHENTICATED) == 0) {
        return false;
    }

    /* Do not rekey if the rekey/key-exchange is in progress */
    if (session->dh_handshake_state != DH_STATE_FINISHED) {
        return false;
    }

    crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_BOTH);
    if (crypto == NULL) {
        return false;
    }

    out_cipher = crypto->out_cipher;
    in_cipher = crypto->in_cipher;

    /* Make sure we can send at least something for very small limits */
    if ((out_cipher->packets == 0) && (in_cipher->packets == 0)) {
        return false;
    }

    /* Time based rekeying */
    if (session->opts.rekey_time != 0 &&
        ssh_timeout_elapsed(&session->last_rekey_time,
                            session->opts.rekey_time)) {
        return true;
    }

    /* RFC4344, Section 3.1 Recommends rekeying after 2^31 packets in either
     * direction to avoid possible information leakage through the MAC tag
     */
    if (out_cipher->packets > MAX_PACKETS ||
        in_cipher->packets > MAX_PACKETS) {
        return true;
    }

    /* Data-based rekeying:
     *  * For outgoing packets we can still delay them
     *  * Incoming packets need to be processed anyway, but we can
     *    signalize our intention to rekey
     */
    next_blocks = payloadsize / out_cipher->blocksize;
    data_rekey_needed = (out_cipher->max_blocks != 0 &&
                         out_cipher->blocks + next_blocks > out_cipher->max_blocks) ||
                         (in_cipher->max_blocks != 0 &&
                         in_cipher->blocks + next_blocks > in_cipher->max_blocks);

    SSH_LOG(SSH_LOG_PACKET,
            "rekey: [data_rekey_needed=%d, out_blocks=%" PRIu64 ", in_blocks=%" PRIu64 "]",
            data_rekey_needed,
            out_cipher->blocks + next_blocks,
            in_cipher->blocks + next_blocks);

    return data_rekey_needed;
}

/* in nonblocking mode, socket_read will read as much as it can, and return */
/* SSH_OK if it has read at least len bytes, otherwise, SSH_AGAIN. */
/* in blocking mode, it will read at least len bytes and will block until it's ok. */

/** @internal
 * @handles a data received event. It then calls the handlers for the different packet types
 * or and exception handler callback.
 * @param user pointer to current ssh_session
 * @param data pointer to the data received
 * @len length of data received. It might not be enough for a complete packet
 * @returns number of bytes read and processed. Zero means only partial packet
 * received and negative value means error.
 */
size_t
ssh_packet_socket_callback(const void *data, size_t receivedlen, void *user)
{
    ssh_session session = (ssh_session)user;
    uint32_t blocksize = 8;
    uint32_t lenfield_blocksize = 8;
    size_t current_macsize = 0;
    uint8_t *ptr = NULL;
    long to_be_read;
    int rc;
    uint8_t *cleartext_packet = NULL;
    uint8_t *packet_second_block = NULL;
    uint8_t *mac = NULL;
    size_t packet_remaining, packet_offset;
    uint32_t packet_len, compsize, payloadsize;
    uint8_t padding;
    size_t processed = 0; /* number of bytes processed from the callback */
    enum ssh_packet_filter_result_e filter_result;
    struct ssh_crypto_struct *crypto = NULL;
    bool etm = false;
    uint32_t etm_packet_offset = 0;
    bool ok;

    crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_IN);
    if (crypto != NULL) {
        current_macsize = hmac_digest_len(crypto->in_hmac);
        blocksize = crypto->in_cipher->blocksize;
        lenfield_blocksize = crypto->in_cipher->lenfield_blocksize;
        etm = crypto->in_hmac_etm;
    }

    if (etm) {
        /* In EtM mode packet size is unencrypted. This means
         * we need to use this offset and set the block size
         * that is part of the encrypted part to 0.
         */
        etm_packet_offset = sizeof(uint32_t);
        lenfield_blocksize = 0;
    } else if (lenfield_blocksize == 0) {
        lenfield_blocksize = blocksize;
    }
    if (data == NULL) {
        goto error;
    }

    if (session->session_state == SSH_SESSION_STATE_ERROR) {
        goto error;
    }
#ifdef DEBUG_PACKET
    SSH_LOG(SSH_LOG_PACKET,
            "rcv packet cb (len=%zu, state=%s)",
            receivedlen,
            session->packet_state == PACKET_STATE_INIT ?
                "INIT" :
                session->packet_state == PACKET_STATE_SIZEREAD ?
                    "SIZE_READ" :
                    session->packet_state == PACKET_STATE_PROCESSING ?
                    "PROCESSING" : "unknown");
#endif
    switch (session->packet_state) {
        case PACKET_STATE_INIT:
            if (receivedlen < lenfield_blocksize + etm_packet_offset) {
                /*
                 * We didn't receive enough data to read either at least one
                 * block size or the unencrypted length in EtM mode.
                 */
#ifdef DEBUG_PACKET
                SSH_LOG(SSH_LOG_PACKET,
                        "Waiting for more data (%zu < %u)",
                        receivedlen,
                        lenfield_blocksize);
#endif
                return 0;
            }

            session->in_packet = (struct packet_struct) {
                .type = 0,
            };

            if (session->in_buffer) {
                rc = ssh_buffer_reinit(session->in_buffer);
                if (rc < 0) {
                    goto error;
                }
            } else {
                session->in_buffer = ssh_buffer_new();
                if (session->in_buffer == NULL) {
                    goto error;
                }
            }

            if (!etm) {
                ptr = ssh_buffer_allocate(session->in_buffer,
                                          lenfield_blocksize);
                if (ptr == NULL) {
                    goto error;
                }
                packet_len = ssh_packet_decrypt_len(session, ptr,
                                                    (uint8_t *)data);
                to_be_read = packet_len - lenfield_blocksize + sizeof(uint32_t);
            } else {
                /* Length is unencrypted in case of Encrypt-then-MAC */
                packet_len = PULL_BE_U32(data, 0);
                to_be_read = packet_len - etm_packet_offset;
            }

            processed += lenfield_blocksize + etm_packet_offset;
            if (packet_len > MAX_PACKET_LEN) {
                ssh_set_error(session,
                              SSH_FATAL,
                              "read_packet(): Packet len too high(%u %.4x)",
                              packet_len, packet_len);
                goto error;
            }
            if (to_be_read < 0) {
                /* remote sshd sends invalid sizes? */
                ssh_set_error(session,
                              SSH_FATAL,
                              "Given numbers of bytes left to be read < 0 (%ld)!",
                              to_be_read);
                goto error;
            }

            session->in_packet.len = packet_len;
            session->packet_state = PACKET_STATE_SIZEREAD;
            FALL_THROUGH;
        case PACKET_STATE_SIZEREAD:
            packet_len = session->in_packet.len;
            packet_offset = processed = lenfield_blocksize + etm_packet_offset;
            to_be_read = packet_len + sizeof(uint32_t) + current_macsize;
            /* if to_be_read is zero, the whole packet was blocksize bytes. */
            if (to_be_read != 0) {
                if (receivedlen < (unsigned long)to_be_read) {
                    /* give up, not enough data in buffer */
                    SSH_LOG(SSH_LOG_PACKET,
                            "packet: partial packet (read len) "
                            "[len=%d, receivedlen=%d, to_be_read=%ld]",
                            packet_len,
                            (int)receivedlen,
                            to_be_read);
                    return 0;
                }

                packet_second_block = (uint8_t*)data + packet_offset;
                processed = to_be_read - current_macsize;
            }

            /* remaining encrypted bytes from the packet, MAC not included */
            packet_remaining = packet_len - (packet_offset - sizeof(uint32_t));
            cleartext_packet = ssh_buffer_allocate(session->in_buffer,
                                                   packet_remaining);
            if (cleartext_packet == NULL) {
                goto error;
            }

            if (packet_second_block != NULL) {
                if (crypto != NULL) {
                    mac = packet_second_block + packet_remaining;

                    if (crypto->in_hmac != SSH_HMAC_NONE && etm) {
                        rc = ssh_packet_hmac_verify(session,
                                                    data,
                                                    processed,
                                                    mac,
                                                    crypto->in_hmac);
                        if (rc < 0) {
                            ssh_set_error(session, SSH_FATAL, "HMAC error");
                            goto error;
                        }
                    }
                    /*
                     * Decrypt the packet. In case of EtM mode, the length is
                     * already known as it's unencrypted. In the other case,
                     * lenfield_blocksize bytes already have been decrypted.
                     */
                    if (packet_remaining > 0) {
                        rc = ssh_packet_decrypt(session,
                                                cleartext_packet,
                                                (uint8_t *)data,
                                                packet_offset,
                                                processed - packet_offset);
                        if (rc < 0) {
                            ssh_set_error(session,
                                          SSH_FATAL,
                                          "Decryption error");
                            goto error;
                        }
                    }

                    if (crypto->in_hmac != SSH_HMAC_NONE && !etm) {
                        ssh_buffer in = session->in_buffer;
                        rc = ssh_packet_hmac_verify(session,
                                                    ssh_buffer_get(in),
                                                    ssh_buffer_get_len(in),
                                                    mac,
                                                    crypto->in_hmac);
                        if (rc < 0) {
                            ssh_set_error(session, SSH_FATAL, "HMAC error");
                            goto error;
                        }
                    }
                    processed += current_macsize;
                } else {
                    memcpy(cleartext_packet,
                           packet_second_block,
                           packet_remaining);
                }
            }

#ifdef WITH_PCAP
            if (session->pcap_ctx != NULL) {
                ssh_pcap_context_write(session->pcap_ctx,
                                       SSH_PCAP_DIR_IN,
                                       ssh_buffer_get(session->in_buffer),
                                       ssh_buffer_get_len(session->in_buffer),
                                       ssh_buffer_get_len(session->in_buffer));
            }
#endif

            if (!etm) {
                /* skip the size field which has been processed before */
                ssh_buffer_pass_bytes(session->in_buffer, sizeof(uint32_t));
            }

            rc = ssh_buffer_get_u8(session->in_buffer, &padding);
            if (rc == 0) {
                ssh_set_error(session,
                              SSH_FATAL,
                              "Packet too short to read padding");
                goto error;
            }

            if (padding > ssh_buffer_get_len(session->in_buffer)) {
                ssh_set_error(session,
                              SSH_FATAL,
                              "Invalid padding: %d (%d left)",
                              padding,
                              ssh_buffer_get_len(session->in_buffer));
                goto error;
            }
            ssh_buffer_pass_bytes_end(session->in_buffer, padding);
            compsize = ssh_buffer_get_len(session->in_buffer);

#ifdef WITH_ZLIB
            if (crypto && crypto->do_compress_in &&
                ssh_buffer_get_len(session->in_buffer) > 0) {
                rc = decompress_buffer(session, session->in_buffer,
                                       MAX_PACKET_LEN);
                if (rc < 0) {
                    goto error;
                }
            }
#endif /* WITH_ZLIB */
            payloadsize = ssh_buffer_get_len(session->in_buffer);
            session->recv_seq++;
            if (crypto != NULL) {
                struct ssh_cipher_struct *cipher = NULL;

                cipher = crypto->in_cipher;
                cipher->packets++;
                cipher->blocks += payloadsize / cipher->blocksize;
            }
            if (session->raw_counter != NULL) {
                session->raw_counter->in_bytes += payloadsize;
                session->raw_counter->in_packets++;
            }

            /*
             * We don't want to rewrite a new packet while still executing the
             * packet callbacks
             */
            session->packet_state = PACKET_STATE_PROCESSING;
            ssh_packet_parse_type(session);
            SSH_LOG(SSH_LOG_PACKET,
                    "packet: read type %hhd [len=%" PRIu32 ",padding=%hhd,"
                    "comp=%" PRIu32 ",payload=%" PRIu32 "]",
                    session->in_packet.type, packet_len, padding, compsize,
                    payloadsize);

            /* Check if the packet is expected */
            filter_result = ssh_packet_incoming_filter(session);

            switch (filter_result) {
            case SSH_PACKET_ALLOWED:
                /* Execute callbacks */
                ssh_packet_process(session, session->in_packet.type);
                break;
            case SSH_PACKET_DENIED:
                ssh_set_error(session,
                              SSH_FATAL,
                              "Packet filter: rejected packet (type %d)",
                              session->in_packet.type);
                goto error;
            case SSH_PACKET_UNKNOWN:
                ssh_packet_send_unimplemented(session, session->recv_seq - 1);
                break;
            }

            session->packet_state = PACKET_STATE_INIT;
            if (processed < receivedlen) {
                /* Handle a potential packet left in socket buffer */
                SSH_LOG(SSH_LOG_PACKET,
                        "Processing %zu bytes left in socket buffer",
                        receivedlen-processed);

                ptr = ((uint8_t*)data) + processed;

                rc = ssh_packet_socket_callback(ptr, receivedlen - processed,
                                                user);
                processed += rc;
            }

            ok = ssh_packet_need_rekey(session, 0);
            if (ok) {
                SSH_LOG(SSH_LOG_PACKET, "Incoming packet triggered rekey");
                rc = ssh_send_rekex(session);
                if (rc != SSH_OK) {
                    SSH_LOG(SSH_LOG_PACKET, "Rekey failed: rc = %d", rc);
                    return rc;
                }
            }

            return processed;
        case PACKET_STATE_PROCESSING:
            SSH_LOG(SSH_LOG_PACKET, "Nested packet processing. Delaying.");
            return 0;
    }

    ssh_set_error(session,
                  SSH_FATAL,
                  "Invalid state into packet_read2(): %d",
                  session->packet_state);

error:
    session->session_state = SSH_SESSION_STATE_ERROR;
    SSH_LOG(SSH_LOG_PACKET, "Packet: processed %zu bytes", processed);
    return processed;
}

static void ssh_packet_socket_controlflow_callback(int code, void *userdata)
{
    ssh_session session = userdata;
    struct ssh_iterator *it;
    ssh_channel channel;

    if (code == SSH_SOCKET_FLOW_WRITEWONTBLOCK) {
        SSH_LOG(SSH_LOG_TRACE, "sending channel_write_wontblock callback");

        /* the out pipe is empty so we can forward this to channels */
        it = ssh_list_get_iterator(session->channels);
        while (it != NULL) {
            channel = ssh_iterator_value(ssh_channel, it);
            ssh_callbacks_execute_list(channel->callbacks,
                                       ssh_channel_callbacks,
                                       channel_write_wontblock_function,
                                       session,
                                       channel,
                                       channel->remote_window);
            it = it->next;
        }
    }
}

void ssh_packet_register_socket_callback(ssh_session session, ssh_socket s)
{
    struct ssh_socket_callbacks_struct *callbacks = &session->socket_callbacks;

    callbacks->data = ssh_packet_socket_callback;
    callbacks->connected = NULL;
    callbacks->controlflow = ssh_packet_socket_controlflow_callback;
    callbacks->userdata = session;
    ssh_socket_set_callbacks(s, callbacks);
}

/** @internal
 * @brief sets the callbacks for the packet layer
 */
void
ssh_packet_set_callbacks(ssh_session session, ssh_packet_callbacks callbacks)
{
    if (session->packet_callbacks == NULL) {
        session->packet_callbacks = ssh_list_new();
        if (session->packet_callbacks == NULL) {
            ssh_set_error_oom(session);
            return;
        }
    }
    ssh_list_append(session->packet_callbacks, callbacks);
}

/** @internal
 * @brief remove the callbacks from the packet layer
 */
void
ssh_packet_remove_callbacks(ssh_session session, ssh_packet_callbacks callbacks)
{
    struct ssh_iterator *it = NULL;

    it = ssh_list_find(session->packet_callbacks, callbacks);
    if (it != NULL) {
        ssh_list_remove(session->packet_callbacks, it);
    }
}

/** @internal
 * @brief sets the default packet handlers
 */
void ssh_packet_set_default_callbacks(ssh_session session)
{
    struct ssh_packet_callbacks_struct *c = &session->default_packet_callbacks;

    c->start = 1;
    c->n_callbacks = sizeof(default_packet_handlers) / sizeof(ssh_packet_callback);
    c->user = session;
    c->callbacks = default_packet_handlers;
    ssh_packet_set_callbacks(session, c);
}

/** @internal
 * @brief dispatch the call of packet handlers callbacks for a received packet
 * @param type type of packet
 */
void ssh_packet_process(ssh_session session, uint8_t type)
{
    struct ssh_iterator *i = NULL;
    int rc = SSH_PACKET_NOT_USED;
    ssh_packet_callbacks cb;

    SSH_LOG(SSH_LOG_PACKET, "Dispatching handler for packet type %d", type);
    if (session->packet_callbacks == NULL) {
        SSH_LOG(SSH_LOG_RARE, "Packet callback is not initialized !");
        return;
    }

    i = ssh_list_get_iterator(session->packet_callbacks);
    while (i != NULL) {
        cb = ssh_iterator_value(ssh_packet_callbacks, i);
        i = i->next;

        if (!cb) {
            continue;
        }

        if (cb->start > type) {
            continue;
        }

        if (cb->start + cb->n_callbacks <= type) {
            continue;
        }

        if (cb->callbacks[type - cb->start] == NULL) {
            continue;
        }

        rc = cb->callbacks[type - cb->start](session, type, session->in_buffer,
                                             cb->user);
        if (rc == SSH_PACKET_USED) {
            break;
        }
    }

    if (rc == SSH_PACKET_NOT_USED) {
        SSH_LOG(SSH_LOG_RARE, "Couldn't do anything with packet type %d", type);
        rc = ssh_packet_send_unimplemented(session, session->recv_seq - 1);
        if (rc != SSH_OK) {
            SSH_LOG(SSH_LOG_RARE, "Failed to send unimplemented: %s",
                    ssh_get_error(session));
        }
    }
}

/** @internal
 * @brief sends a SSH_MSG_UNIMPLEMENTED answer to an unhandled packet
 * @param session the SSH session
 * @param seqnum the sequence number of the unknown packet
 * @return SSH_ERROR on error, else SSH_OK
 */
int ssh_packet_send_unimplemented(ssh_session session, uint32_t seqnum){
    int rc;

    rc = ssh_buffer_pack(session->out_buffer,
                         "bd",
                         SSH2_MSG_UNIMPLEMENTED,
                         seqnum);
    if (rc != SSH_OK) {
        ssh_set_error_oom(session);
        return SSH_ERROR;
    }
    rc = ssh_packet_send(session);

    return rc;
}

/** @internal
 * @brief handles a SSH_MSG_UNIMPLEMENTED packet
 */
SSH_PACKET_CALLBACK(ssh_packet_unimplemented){
    uint32_t seq;
    int rc;

    (void)session; /* unused */
    (void)type;
    (void)user;

    rc = ssh_buffer_unpack(packet, "d", &seq);
    if (rc != SSH_OK) {
        SSH_LOG(SSH_LOG_WARNING,
                "Could not unpack SSH_MSG_UNIMPLEMENTED packet");
    }

    SSH_LOG(SSH_LOG_RARE,
            "Received SSH_MSG_UNIMPLEMENTED (sequence number %d)",seq);

    return SSH_PACKET_USED;
}

/** @internal
 * @parse the "Type" header field of a packet and updates the session
 */
int ssh_packet_parse_type(struct ssh_session_struct *session)
{
    session->in_packet = (struct packet_struct) {
        .type = 0,
    };

    if (session->in_buffer == NULL) {
        return SSH_ERROR;
    }

    if (ssh_buffer_get_u8(session->in_buffer, &session->in_packet.type) == 0) {
        ssh_set_error(session, SSH_FATAL, "Packet too short to read type");
        return SSH_ERROR;
    }

    session->in_packet.valid = 1;

    return SSH_OK;
}

/*
 * This function places the outgoing packet buffer into an outgoing
 * socket buffer
 */
static int ssh_packet_write(ssh_session session) {
  int rc = SSH_ERROR;

  rc=ssh_socket_write(session->socket,
      ssh_buffer_get(session->out_buffer),
      ssh_buffer_get_len(session->out_buffer));

  return rc;
}

static int packet_send2(ssh_session session)
{
    unsigned int blocksize = 8;
    unsigned int lenfield_blocksize = 0;
    enum ssh_hmac_e hmac_type;
    uint32_t currentlen = ssh_buffer_get_len(session->out_buffer);
    struct ssh_crypto_struct *crypto = NULL;
    unsigned char *hmac = NULL;
    uint8_t padding_data[32] = { 0 };
    uint8_t padding_size;
    uint32_t finallen, payloadsize, compsize;
    uint8_t header[5] = {0};
    uint8_t type, *payload;
    int rc = SSH_ERROR;
    bool etm = false;
    int etm_packet_offset = 0;

    crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_OUT);
    if (crypto) {
        blocksize = crypto->out_cipher->blocksize;
        lenfield_blocksize = crypto->out_cipher->lenfield_blocksize;
        hmac_type = crypto->out_hmac;
        etm = crypto->out_hmac_etm;
    } else {
        hmac_type = session->next_crypto->out_hmac;
    }

    payload = (uint8_t *)ssh_buffer_get(session->out_buffer);
    type = payload[0]; /* type is the first byte of the packet now */

    payloadsize = currentlen;
    if (etm) {
        etm_packet_offset = sizeof(uint32_t);
        lenfield_blocksize = 0;
    }

#ifdef WITH_ZLIB
    if (crypto != NULL && crypto->do_compress_out &&
        ssh_buffer_get_len(session->out_buffer) > 0) {
        rc = compress_buffer(session,session->out_buffer);
        if (rc < 0) {
            goto error;
        }
        currentlen = ssh_buffer_get_len(session->out_buffer);
    }
#endif /* WITH_ZLIB */
    compsize = currentlen;
    /* compressed payload + packet len (4) + padding_size len (1) */
    /* totallen - lenfield_blocksize - etm_packet_offset must be equal to 0 (mod blocksize) */
    padding_size = (blocksize - ((blocksize - lenfield_blocksize - etm_packet_offset + currentlen + 5) % blocksize));
    if (padding_size < 4) {
        padding_size += blocksize;
    }

    if (crypto != NULL) {
        int ok;

        ok = ssh_get_random(padding_data, padding_size, 0);
        if (!ok) {
            ssh_set_error(session, SSH_FATAL, "PRNG error");
            goto error;
        }
    }

    finallen = currentlen - etm_packet_offset + padding_size + 1;

    PUSH_BE_U32(header, 0, finallen);
    PUSH_BE_U8(header, 4, padding_size);

    rc = ssh_buffer_prepend_data(session->out_buffer,
                                 header,
                                 sizeof(header));
    if (rc < 0) {
        goto error;
    }

    rc = ssh_buffer_add_data(session->out_buffer, padding_data, padding_size);
    if (rc < 0) {
        goto error;
    }

#ifdef WITH_PCAP
    if (session->pcap_ctx != NULL) {
        ssh_pcap_context_write(session->pcap_ctx,
                               SSH_PCAP_DIR_OUT,
                               ssh_buffer_get(session->out_buffer),
                               ssh_buffer_get_len(session->out_buffer),
                               ssh_buffer_get_len(session->out_buffer));
    }
#endif

    hmac = ssh_packet_encrypt(session,
                              ssh_buffer_get(session->out_buffer),
                              ssh_buffer_get_len(session->out_buffer));
    /* XXX This returns null before switching on crypto, with none MAC
     * and on various errors.
     * We should distinguish between these cases to avoid hiding errors. */
    if (hmac != NULL) {
        rc = ssh_buffer_add_data(session->out_buffer,
                                 hmac,
                                 hmac_digest_len(hmac_type));
        if (rc < 0) {
            goto error;
        }
    }

    rc = ssh_packet_write(session);
    if (rc == SSH_ERROR) {
        goto error;
    }
    session->send_seq++;
    if (crypto != NULL) {
        struct ssh_cipher_struct *cipher = NULL;

        cipher = crypto->out_cipher;
        cipher->packets++;
        cipher->blocks += payloadsize / cipher->blocksize;
    }
    if (session->raw_counter != NULL) {
        session->raw_counter->out_bytes += payloadsize;
        session->raw_counter->out_packets++;
    }

    SSH_LOG(SSH_LOG_PACKET,
            "packet: wrote [type=%u, len=%u, padding_size=%hhd, comp=%u, "
            "payload=%u]",
            type,
            finallen,
            padding_size,
            compsize,
            payloadsize);

    rc = ssh_buffer_reinit(session->out_buffer);
    if (rc < 0) {
        rc = SSH_ERROR;
        goto error;
    }

    /* We sent the NEWKEYS so any further packet needs to be encrypted
     * with the new keys. We can not switch both directions (need to decrypt
     * peer NEWKEYS) and we do not want to wait for the peer NEWKEYS
     * too, so we will switch only the OUT direction now.
     */
    if (type == SSH2_MSG_NEWKEYS) {
        rc = ssh_packet_set_newkeys(session, SSH_DIRECTION_OUT);
    }
error:
    return rc; /* SSH_OK, AGAIN or ERROR */
}

static bool
ssh_packet_is_kex(unsigned char type)
{
    return type >= SSH2_MSG_DISCONNECT &&
           type <= SSH2_MSG_KEX_DH_GEX_REQUEST &&
           type != SSH2_MSG_SERVICE_REQUEST &&
           type != SSH2_MSG_SERVICE_ACCEPT &&
           type != SSH2_MSG_IGNORE &&
           type != SSH2_MSG_EXT_INFO;
}

static bool
ssh_packet_in_rekey(ssh_session session)
{
    /* We know we are rekeying if we are authenticated and the DH
     * status is not finished, but we only queue packets until we've
     * sent our NEWKEYS.
     */
    return (session->flags & SSH_SESSION_FLAG_AUTHENTICATED) &&
           (session->dh_handshake_state != DH_STATE_FINISHED) &&
           (session->dh_handshake_state != DH_STATE_NEWKEYS_SENT);
}

int ssh_packet_send(ssh_session session)
{
    uint32_t payloadsize;
    uint8_t type, *payload;
    bool need_rekey, in_rekey;
    int rc;

    payloadsize = ssh_buffer_get_len(session->out_buffer);
    if (payloadsize < 1) {
        return SSH_ERROR;
    }

    payload = (uint8_t *)ssh_buffer_get(session->out_buffer);
    type = payload[0]; /* type is the first byte of the packet now */
    need_rekey = ssh_packet_need_rekey(session, payloadsize);
    in_rekey = ssh_packet_in_rekey(session);

    /* The rekey is triggered here. After that, only the key exchange
     * packets can be sent, until we send our NEWKEYS.
     */
    if (need_rekey || (in_rekey && !ssh_packet_is_kex(type))) {
        if (need_rekey) {
            SSH_LOG(SSH_LOG_PACKET, "Outgoing packet triggered rekey");
        }
        /* Queue the current packet -- we will send it after the rekey */
        SSH_LOG(SSH_LOG_PACKET, "Queuing packet type %d", type);
        rc = ssh_list_append(session->out_queue, session->out_buffer);
        if (rc != SSH_OK) {
            return SSH_ERROR;
        }
        session->out_buffer = ssh_buffer_new();
        if (session->out_buffer == NULL) {
            ssh_set_error_oom(session);
            return SSH_ERROR;
        }

        if (need_rekey) {
            /* Send the KEXINIT packet instead.
             * This recursively calls the packet_send(), but it should
             * not get into rekeying again.
             * After that we need to handle the key exchange responses
             * up to the point where we can send the rest of the queue.
             */
            return ssh_send_rekex(session);
        }
        return SSH_OK;
    }

    /* Send the packet normally */
    rc = packet_send2(session);

    /* We finished the key exchange so we can try to send our queue now */
    if (rc == SSH_OK && type == SSH2_MSG_NEWKEYS) {
        struct ssh_iterator *it;

        for (it = ssh_list_get_iterator(session->out_queue);
             it != NULL;
             it = ssh_list_get_iterator(session->out_queue)) {
            struct ssh_buffer_struct *next_buffer = NULL;

            /* Peek only -- do not remove from queue yet */
            next_buffer = (struct ssh_buffer_struct *)it->data;
            payloadsize = ssh_buffer_get_len(next_buffer);
            if (ssh_packet_need_rekey(session, payloadsize)) {
                /* Sigh ... we still can not send this packet. Repeat. */
                SSH_LOG(SSH_LOG_PACKET, "Queued packet triggered rekey");
                return ssh_send_rekex(session);
            }
            SSH_BUFFER_FREE(session->out_buffer);
            session->out_buffer = ssh_list_pop_head(struct ssh_buffer_struct *,
                                                    session->out_queue);
            payload = (uint8_t *)ssh_buffer_get(session->out_buffer);
            type = payload[0];
            SSH_LOG(SSH_LOG_PACKET, "Dequeue packet type %d", type);
            rc = packet_send2(session);
            if (rc != SSH_OK) {
                return rc;
            }
        }
    }

    return rc;
}

static void
ssh_init_rekey_state(struct ssh_session_struct *session,
                     struct ssh_cipher_struct *cipher)
{
    /* Reset the counters: should be NOOP */
    cipher->packets = 0;
    cipher->blocks = 0;

    /* Default rekey limits for ciphers as specified in RFC4344, Section 3.2 */
    if (cipher->blocksize >= 16) {
        /* For larger block size (L bits) use maximum of 2**(L/4) blocks */
        cipher->max_blocks = (uint64_t)1 << (cipher->blocksize*2);
    } else {
        /* For smaller blocks use limit of 1 GB as recommended in RFC4253 */
        cipher->max_blocks = ((uint64_t)1 << 30) / cipher->blocksize;
    }
    /* If we have limit provided by user, use the smaller one */
    if (session->opts.rekey_data != 0) {
        cipher->max_blocks = MIN(cipher->max_blocks,
                                 session->opts.rekey_data / cipher->blocksize);
    }

    SSH_LOG(SSH_LOG_PROTOCOL,
            "Set rekey after %" PRIu64 " blocks",
            cipher->max_blocks);
}

/*
 * Once we got SSH2_MSG_NEWKEYS we can switch next_crypto and
 * current_crypto for our desired direction
 */
int
ssh_packet_set_newkeys(ssh_session session,
                       enum ssh_crypto_direction_e direction)
{
    struct ssh_cipher_struct *in_cipher = NULL, *out_cipher = NULL;
    int rc;

    SSH_LOG(SSH_LOG_TRACE,
            "called, direction =%s%s",
            direction & SSH_DIRECTION_IN ? " IN " : "",
            direction & SSH_DIRECTION_OUT ? " OUT " : "");

    if (session->next_crypto == NULL) {
        return SSH_ERROR;
    }

    session->next_crypto->used |= direction;
    if (session->current_crypto != NULL) {
        if (session->current_crypto->used & direction) {
            SSH_LOG(SSH_LOG_WARNING, "This direction isn't used anymore.");
        }
        /* Mark the current requested direction unused */
        session->current_crypto->used &= ~direction;
    }

    /* Both sides switched: do the actual switch now */
    if (session->next_crypto->used == SSH_DIRECTION_BOTH) {
        size_t session_id_len;

        if (session->current_crypto != NULL) {
            crypto_free(session->current_crypto);
            session->current_crypto = NULL;
        }

        session->current_crypto = session->next_crypto;
        session->current_crypto->used = SSH_DIRECTION_BOTH;

        /* Initialize the next_crypto structure */
        session->next_crypto = crypto_new();
        if (session->next_crypto == NULL) {
            ssh_set_error_oom(session);
            return SSH_ERROR;
        }

        session_id_len = session->current_crypto->session_id_len;
        session->next_crypto->session_id = malloc(session_id_len);
        if (session->next_crypto->session_id == NULL) {
            ssh_set_error_oom(session);
            return SSH_ERROR;
        }

        memcpy(session->next_crypto->session_id,
               session->current_crypto->session_id,
               session_id_len);
        session->next_crypto->session_id_len = session_id_len;

        return SSH_OK;
    }

    /* Initialize common structures so the next context can be used in
     * either direction */
    if (session->client) {
        /* The server has this part already done */
        rc = ssh_make_sessionid(session);
        if (rc != SSH_OK) {
            return SSH_ERROR;
        }

        /*
         * Set the cryptographic functions for the next crypto
         * (it is needed for ssh_generate_session_keys for key lengths)
         */
        rc = crypt_set_algorithms_client(session);
        if (rc < 0) {
            return SSH_ERROR;
        }
    }

    if (ssh_generate_session_keys(session) < 0) {
        return SSH_ERROR;
    }

    in_cipher = session->next_crypto->in_cipher;
    out_cipher = session->next_crypto->out_cipher;
    if (in_cipher == NULL || out_cipher == NULL) {
        return SSH_ERROR;
    }

    /* Initialize rekeying states */
    ssh_init_rekey_state(session, out_cipher);
    ssh_init_rekey_state(session, in_cipher);
    if (session->opts.rekey_time != 0) {
        ssh_timestamp_init(&session->last_rekey_time);
        SSH_LOG(SSH_LOG_PROTOCOL, "Set rekey after %" PRIu32 " seconds",
                session->opts.rekey_time/1000);
    }

    if (in_cipher->set_decrypt_key) {
        /* Initialize the encryption and decryption keys in next_crypto */
        rc = in_cipher->set_decrypt_key(in_cipher,
                                        session->next_crypto->decryptkey,
                                        session->next_crypto->decryptIV);
        if (rc < 0) {
            /* On error, make sure it is not used */
            session->next_crypto->used = 0;
            return SSH_ERROR;
        }
    }

    if (out_cipher->set_encrypt_key) {
        rc = out_cipher->set_encrypt_key(out_cipher,
                                         session->next_crypto->encryptkey,
                                         session->next_crypto->encryptIV);
        if (rc < 0) {
            /* On error, make sure it is not used */
            session->next_crypto->used = 0;
            return SSH_ERROR;
        }
    }

    return SSH_OK;
}