session.c

/* Copyright (C) Sara Golemon <sarag@libssh2.org>
 * Copyright (C) Daniel Stenberg
 * Copyright (C) Simon Josefsson <simon@josefsson.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms,
 * with or without modification, are permitted provided
 * that the following conditions are met:
 *
 *   Redistributions of source code must retain the above
 *   copyright notice, this list of conditions and the
 *   following disclaimer.
 *
 *   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.
 *
 *   Neither the name of the copyright holder nor the names
 *   of any other contributors may be used to endorse or
 *   promote products derived from this software without
 *   specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "libssh2_priv.h"

#ifdef _WIN32
#include <ws2tcpip.h>  /* for socklen_t */
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_ALLOCA_H
#include <alloca.h>
#endif

#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>

#include "transport.h"
#include "session.h"
#include "channel.h"
#include "mac.h"

#if defined(_WIN32)
#define libssh2_usec_t long
#elif defined(__APPLE__)
#define libssh2_usec_t suseconds_t
#else
#undef libssh2_usec_t
#endif

/* libssh2_default_alloc
 */
static
LIBSSH2_ALLOC_FUNC(libssh2_default_alloc)
{
    (void)abstract;
    return malloc(count);
}

/* libssh2_default_free
 */
static
LIBSSH2_FREE_FUNC(libssh2_default_free)
{
    (void)abstract;
    free(ptr);
}

/* libssh2_default_realloc
 */
static
LIBSSH2_REALLOC_FUNC(libssh2_default_realloc)
{
    (void)abstract;
    return realloc(ptr, count);
}

/*
 * banner_receive
 *
 * Wait for a hello from the remote host
 * Allocate a buffer and store the banner in session->remote.banner
 * Returns: 0 on success, LIBSSH2_ERROR_EAGAIN if read would block, negative
 * on failure
 */
static int
banner_receive(LIBSSH2_SESSION * session)
{
    ssize_t ret;
    size_t banner_len;

    if(session->banner_TxRx_state == libssh2_NB_state_idle) {
        banner_len = 0;

        session->banner_TxRx_state = libssh2_NB_state_created;
    }
    else {
        banner_len = session->banner_TxRx_total_send;
    }

    while((banner_len < sizeof(session->banner_TxRx_banner)) &&
          ((banner_len == 0)
           || (session->banner_TxRx_banner[banner_len - 1] != '\n'))) {
        char c = '\0';

        /* no incoming block yet! */
        session->socket_block_directions &= ~LIBSSH2_SESSION_BLOCK_INBOUND;

        ret = LIBSSH2_RECV(session, &c, 1,
                           LIBSSH2_SOCKET_RECV_FLAGS(session));
        if(ret < 0) {
            if(session->api_block_mode || (ret != -EAGAIN))
                /* ignore EAGAIN when non-blocking */
                _libssh2_debug((session, LIBSSH2_TRACE_SOCKET,
                               "Error recving %d bytes: %d", 1, (int)-ret));
        }
        else
            _libssh2_debug((session, LIBSSH2_TRACE_SOCKET,
                           "Recved %d bytes banner", (int)ret));

        if(ret < 0) {
            if(ret == -EAGAIN) {
                session->socket_block_directions =
                    LIBSSH2_SESSION_BLOCK_INBOUND;
                session->banner_TxRx_total_send = banner_len;
                return LIBSSH2_ERROR_EAGAIN;
            }

            /* Some kinda error */
            session->banner_TxRx_state = libssh2_NB_state_idle;
            session->banner_TxRx_total_send = 0;
            return LIBSSH2_ERROR_SOCKET_RECV;
        }

        if(ret == 0) {
            session->socket_state = LIBSSH2_SOCKET_DISCONNECTED;
            return LIBSSH2_ERROR_SOCKET_DISCONNECT;
        }

        if((c == '\r' || c == '\n') && banner_len == 0) {
            continue;
        }

        if(c == '\0') {
            /* NULLs are not allowed in SSH banners */
            session->banner_TxRx_state = libssh2_NB_state_idle;
            session->banner_TxRx_total_send = 0;
            return LIBSSH2_ERROR_BANNER_RECV;
        }

        session->banner_TxRx_banner[banner_len++] = c;
    }

    while(banner_len &&
          ((session->banner_TxRx_banner[banner_len - 1] == '\n') ||
           (session->banner_TxRx_banner[banner_len - 1] == '\r'))) {
        banner_len--;
    }

    /* From this point on, we are done here */
    session->banner_TxRx_state = libssh2_NB_state_idle;
    session->banner_TxRx_total_send = 0;

    if(!banner_len)
        return LIBSSH2_ERROR_BANNER_RECV;

    if(session->remote.banner)
        LIBSSH2_FREE(session, session->remote.banner);

    session->remote.banner = LIBSSH2_ALLOC(session, banner_len + 1);
    if(!session->remote.banner) {
        return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                              "Error allocating space for remote banner");
    }
    memcpy(session->remote.banner, session->banner_TxRx_banner, banner_len);
    session->remote.banner[banner_len] = '\0';
    _libssh2_debug((session, LIBSSH2_TRACE_TRANS, "Received Banner: %s",
                   session->remote.banner));
    return LIBSSH2_ERROR_NONE;
}

/*
 * banner_send
 *
 * Send the default banner, or the one set via libssh2_setopt_string
 *
 * Returns LIBSSH2_ERROR_EAGAIN if it would block - and if it does so, you
 * should call this function again as soon as it is likely that more data can
 * be sent, and this function should then be called with the same argument set
 * (same data pointer and same data_len) until zero or failure is returned.
 */
static int
banner_send(LIBSSH2_SESSION * session)
{
    char *banner = (char *) LIBSSH2_SSH_DEFAULT_BANNER_WITH_CRLF;
    size_t banner_len = sizeof(LIBSSH2_SSH_DEFAULT_BANNER_WITH_CRLF) - 1;
    ssize_t ret;

    if(session->banner_TxRx_state == libssh2_NB_state_idle) {
        if(session->local.banner) {
            /* setopt_string will have given us our \r\n characters */
            banner_len = strlen((char *) session->local.banner);
            banner = (char *) session->local.banner;
        }
#ifdef LIBSSH2DEBUG
        {
            char banner_dup[256];

            /* Hack and slash to avoid sending CRLF in debug output */
            if(banner_len < 256) {
                memcpy(banner_dup, banner, banner_len - 2);
                banner_dup[banner_len - 2] = '\0';
            }
            else {
                memcpy(banner_dup, banner, 255);
                banner_dup[255] = '\0';
            }

            _libssh2_debug((session, LIBSSH2_TRACE_TRANS,
                           "Sending Banner: %s", banner_dup));
        }
#endif

        session->banner_TxRx_state = libssh2_NB_state_created;
    }

    /* no outgoing block yet! */
    session->socket_block_directions &= ~LIBSSH2_SESSION_BLOCK_OUTBOUND;

    ret = LIBSSH2_SEND(session,
                       banner + session->banner_TxRx_total_send,
                       banner_len - session->banner_TxRx_total_send,
                       LIBSSH2_SOCKET_SEND_FLAGS(session));
    if(ret < 0)
        _libssh2_debug((session, LIBSSH2_TRACE_SOCKET,
                       "Error sending %d bytes: %d",
                       banner_len - session->banner_TxRx_total_send, -ret));
    else
        _libssh2_debug((session, LIBSSH2_TRACE_SOCKET,
                       "Sent %d/%d bytes at %p+%d", ret,
                       banner_len - session->banner_TxRx_total_send,
                       banner, session->banner_TxRx_total_send));

    if(ret != (ssize_t)(banner_len - session->banner_TxRx_total_send)) {
        if(ret >= 0 || ret == -EAGAIN) {
            /* the whole packet could not be sent, save the what was */
            session->socket_block_directions =
                LIBSSH2_SESSION_BLOCK_OUTBOUND;
            if(ret > 0)
                session->banner_TxRx_total_send += ret;
            return LIBSSH2_ERROR_EAGAIN;
        }
        session->banner_TxRx_state = libssh2_NB_state_idle;
        session->banner_TxRx_total_send = 0;
        return LIBSSH2_ERROR_SOCKET_RECV;
    }

    /* Set the state back to idle */
    session->banner_TxRx_state = libssh2_NB_state_idle;
    session->banner_TxRx_total_send = 0;

    return 0;
}

/*
 * session_nonblock() sets the given socket to either blocking or
 * non-blocking mode based on the 'nonblock' boolean argument. This function
 * is copied from the libcurl sources with permission.
 */
static int
session_nonblock(libssh2_socket_t sockfd,   /* operate on this */
                 int nonblock /* TRUE or FALSE */ )
{
#ifdef HAVE_O_NONBLOCK
    /* most recent unix versions */
    int flags;

    flags = fcntl(sockfd, F_GETFL, 0);
    if(nonblock)
        return fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
    else
        return fcntl(sockfd, F_SETFL, flags & (~O_NONBLOCK));
#elif defined(HAVE_FIONBIO)
    /* older unix versions and VMS */
    int flags;

    flags = nonblock;
    return ioctl(sockfd, FIONBIO, &flags);
#elif defined(HAVE_IOCTLSOCKET_CASE)
    /* presumably for Amiga */
    return IoctlSocket(sockfd, FIONBIO, (long) nonblock);
#elif defined(HAVE_SO_NONBLOCK)
    /* BeOS */
    long b = nonblock ? 1 : 0;
    return setsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b));
#elif defined(_WIN32)
    unsigned long flags;

    flags = nonblock;
    return ioctlsocket(sockfd, FIONBIO, &flags);
#else
    (void)sockfd;
    (void)nonblock;
    return 0;                   /* returns success */
#endif
}

/*
 * get_socket_nonblocking
 *
 * gets the given blocking or non-blocking state of the socket.
 */
static int
get_socket_nonblocking(libssh2_socket_t sockfd)
{                               /* operate on this */
#ifdef HAVE_O_NONBLOCK
    /* most recent unix versions */
    int flags = fcntl(sockfd, F_GETFL, 0);

    if(flags == -1) {
        /* Assume blocking on error */
        return 1;
    }
    return (flags & O_NONBLOCK);
#elif defined(HAVE_SO_NONBLOCK)
    /* BeOS */
    long b;
    if(getsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b))) {
        /* Assume blocking on error */
        return 1;
    }
    return (int) b;
#elif defined(SO_STATE) && defined(__VMS)
    /* VMS TCP/IP Services */

    size_t sockstat = 0;
    int    callstat = 0;
    size_t size = sizeof(int);

    callstat = getsockopt(sockfd, SOL_SOCKET, SO_STATE,
                          (char *)&sockstat, &size);
    if(callstat == -1) {
        return 0;
    }
    if((sockstat&SS_NBIO) != 0) {
        return 1;
    }
    return 0;
#elif defined(_WIN32)
    unsigned int option_value;
    socklen_t option_len = sizeof(option_value);

    if(getsockopt(sockfd, SOL_SOCKET, SO_ERROR,
                  (void *) &option_value, &option_len)) {
        /* Assume blocking on error */
        return 1;
    }
    return (int) option_value;
#else
    (void)sockfd;
    return 1;                   /* returns blocking */
#endif
}

/* libssh2_session_banner_set
 * Set the local banner to use in the server handshake.
 */
LIBSSH2_API int
libssh2_session_banner_set(LIBSSH2_SESSION * session, const char *banner)
{
    size_t banner_len = banner ? strlen(banner) : 0;

    if(session->local.banner) {
        LIBSSH2_FREE(session, session->local.banner);
        session->local.banner = NULL;
    }

    if(!banner_len)
        return 0;

    session->local.banner = LIBSSH2_ALLOC(session, banner_len + 3);
    if(!session->local.banner) {
        return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                              "Unable to allocate memory for local banner");
    }

    memcpy(session->local.banner, banner, banner_len);

    /* first zero terminate like this so that the debug output is nice */
    session->local.banner[banner_len] = '\0';
    _libssh2_debug((session, LIBSSH2_TRACE_TRANS, "Setting local Banner: %s",
                   session->local.banner));
    session->local.banner[banner_len++] = '\r';
    session->local.banner[banner_len++] = '\n';
    session->local.banner[banner_len] = '\0';

    return 0;
}

/* libssh2_banner_set
 * Set the local banner. DEPRECATED VERSION
 */
LIBSSH2_API int
libssh2_banner_set(LIBSSH2_SESSION * session, const char *banner)
{
    return libssh2_session_banner_set(session, banner);
}

/*
 * libssh2_session_init_ex
 *
 * Allocate and initialize a libssh2 session structure. Allows for malloc
 * callbacks in case the calling program has its own memory manager It's
 * allowable (but unadvisable) to define some but not all of the malloc
 * callbacks An additional pointer value may be optionally passed to be sent
 * to the callbacks (so they know who's asking)
 */
LIBSSH2_API LIBSSH2_SESSION *
libssh2_session_init_ex(LIBSSH2_ALLOC_FUNC((*my_alloc)),
                        LIBSSH2_FREE_FUNC((*my_free)),
                        LIBSSH2_REALLOC_FUNC((*my_realloc)), void *abstract)
{
    LIBSSH2_ALLOC_FUNC((*local_alloc)) = libssh2_default_alloc;
    LIBSSH2_FREE_FUNC((*local_free)) = libssh2_default_free;
    LIBSSH2_REALLOC_FUNC((*local_realloc)) = libssh2_default_realloc;
    LIBSSH2_SESSION *session;

    if(my_alloc) {
        local_alloc = my_alloc;
    }
    if(my_free) {
        local_free = my_free;
    }
    if(my_realloc) {
        local_realloc = my_realloc;
    }

    session = local_alloc(sizeof(LIBSSH2_SESSION), &abstract);
    if(session) {
        memset(session, 0, sizeof(LIBSSH2_SESSION));
        session->alloc = local_alloc;
        session->free = local_free;
        session->realloc = local_realloc;
        session->send = _libssh2_send;
        session->recv = _libssh2_recv;
        session->abstract = abstract;
        session->api_timeout = 0; /* timeout-free API by default */
        session->api_block_mode = 1; /* blocking API by default */
        session->packet_read_timeout = LIBSSH2_DEFAULT_READ_TIMEOUT;
        session->flag.quote_paths = 1; /* default behavior is to quote paths
                                          for the scp subsystem */
        _libssh2_debug((session, LIBSSH2_TRACE_TRANS,
                       "New session resource allocated"));
        _libssh2_init_if_needed();
    }
    return session;
}

/*
 * libssh2_session_callback_set
 *
 * Set (or reset) a callback function
 * Returns the prior address
 *
 * ALERT: this function relies on that we can typecast function pointers
 * to void pointers, which isn't allowed in ISO C!
 */
#ifdef _MSC_VER
#pragma warning(push)
/* nonstandard extension, function/data pointer conversion in expression */
#pragma warning(disable:4152)
#else
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"
#endif
LIBSSH2_API void *
libssh2_session_callback_set(LIBSSH2_SESSION * session,
                             int cbtype, void *callback)
{
    void *oldcb;

    switch(cbtype) {
    case LIBSSH2_CALLBACK_IGNORE:
        oldcb = session->ssh_msg_ignore;
        session->ssh_msg_ignore = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_DEBUG:
        oldcb = session->ssh_msg_debug;
        session->ssh_msg_debug = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_DISCONNECT:
        oldcb = session->ssh_msg_disconnect;
        session->ssh_msg_disconnect = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_MACERROR:
        oldcb = session->macerror;
        session->macerror = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_X11:
        oldcb = session->x11;
        session->x11 = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_SEND:
        oldcb = session->send;
        session->send = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_RECV:
        oldcb = session->recv;
        session->recv = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_AUTHAGENT:
        oldcb = session->authagent;
        session->authagent = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_AUTHAGENT_IDENTITIES:
        oldcb = session->addLocalIdentities;
        session->addLocalIdentities = callback;
        return oldcb;

    case LIBSSH2_CALLBACK_AUTHAGENT_SIGN:
        oldcb = session->agentSignCallback;
        session->agentSignCallback = callback;
        return oldcb;
    }
    _libssh2_debug((session, LIBSSH2_TRACE_TRANS, "Setting Callback %d",
                   cbtype));

    return NULL;
}
#ifdef _MSC_VER
#pragma warning(pop)
#else
#pragma GCC diagnostic pop
#endif

/*
 * _libssh2_wait_socket
 *
 * Utility function that waits for action on the socket. Returns 0 when ready
 * to run again or error on timeout.
 */
int _libssh2_wait_socket(LIBSSH2_SESSION *session, time_t start_time)
{
    int rc;
    int seconds_to_next;
    int dir;
    int has_timeout;
    long ms_to_next = 0;
    long elapsed_ms;

    /* since libssh2 often sets EAGAIN internally before this function is
       called, we can decrease some amount of confusion in user programs by
       resetting the error code in this function to reduce the risk of EAGAIN
       being stored as error when a blocking function has returned */
    session->err_code = LIBSSH2_ERROR_NONE;

    rc = libssh2_keepalive_send(session, &seconds_to_next);
    if(rc)
        return rc;

    ms_to_next = seconds_to_next * 1000;

    /* figure out what to wait for */
    dir = libssh2_session_block_directions(session);

    if(!dir) {
        _libssh2_debug((session, LIBSSH2_TRACE_SOCKET,
                       "Nothing to wait for in wait_socket"));
        /* To avoid that we hang below just because there's nothing set to
           wait for, we timeout on 1 second to also avoid busy-looping
           during this condition */
        ms_to_next = 1000;
    }

    if(session->api_timeout > 0 &&
        (seconds_to_next == 0 ||
         ms_to_next > session->api_timeout)) {
        time_t now = time(NULL);
        elapsed_ms = (long)(1000*difftime(now, start_time));
        if(elapsed_ms > session->api_timeout) {
            return _libssh2_error(session, LIBSSH2_ERROR_TIMEOUT,
                                  "API timeout expired");
        }
        ms_to_next = (session->api_timeout - elapsed_ms);
        has_timeout = 1;
    }
    else if(ms_to_next > 0) {
        has_timeout = 1;
    }
    else
        has_timeout = 0;

#ifdef HAVE_POLL
    {
        struct pollfd sockets[1];

        sockets[0].fd = session->socket_fd;
        sockets[0].events = 0;
        sockets[0].revents = 0;

        if(dir & LIBSSH2_SESSION_BLOCK_INBOUND)
            sockets[0].events |= POLLIN;

        if(dir & LIBSSH2_SESSION_BLOCK_OUTBOUND)
            sockets[0].events |= POLLOUT;

        rc = poll(sockets, 1, has_timeout ? (int)ms_to_next : -1);
    }
#else
    {
        fd_set rfd;
        fd_set wfd;
        fd_set *writefd = NULL;
        fd_set *readfd = NULL;
        struct timeval tv;

        tv.tv_sec = ms_to_next / 1000;
#ifdef libssh2_usec_t
        tv.tv_usec = (libssh2_usec_t)((ms_to_next - tv.tv_sec*1000) * 1000);
#else
        tv.tv_usec = (ms_to_next - tv.tv_sec*1000) * 1000;
#endif

        if(dir & LIBSSH2_SESSION_BLOCK_INBOUND) {
            FD_ZERO(&rfd);
            FD_SET(session->socket_fd, &rfd);
            readfd = &rfd;
        }

        if(dir & LIBSSH2_SESSION_BLOCK_OUTBOUND) {
            FD_ZERO(&wfd);
            FD_SET(session->socket_fd, &wfd);
            writefd = &wfd;
        }

        rc = select((int)(session->socket_fd + 1), readfd, writefd, NULL,
                    has_timeout ? &tv : NULL);
    }
#endif
    if(rc == 0) {
        return _libssh2_error(session, LIBSSH2_ERROR_TIMEOUT,
                              "Timed out waiting on socket");
    }
    if(rc < 0) {
        return _libssh2_error(session, LIBSSH2_ERROR_TIMEOUT,
                              "Error waiting on socket");
    }

    return 0; /* ready to try again */
}

static int
session_startup(LIBSSH2_SESSION *session, libssh2_socket_t sock)
{
    int rc;

    if(session->startup_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_TRANS,
                       "session_startup for socket %d", sock));
        if(LIBSSH2_INVALID_SOCKET == sock) {
            /* Did we forget something? */
            return _libssh2_error(session, LIBSSH2_ERROR_BAD_SOCKET,
                                  "Bad socket provided");
        }
        session->socket_fd = sock;

        session->socket_prev_blockstate =
            !get_socket_nonblocking(session->socket_fd);

        if(session->socket_prev_blockstate) {
            /* If in blocking state change to non-blocking */
            rc = session_nonblock(session->socket_fd, 1);
            if(rc) {
                return _libssh2_error(session, rc,
                                      "Failed changing socket's "
                                      "blocking state to non-blocking");
            }
        }

        session->startup_state = libssh2_NB_state_created;
    }

    if(session->startup_state == libssh2_NB_state_created) {
        rc = banner_send(session);
        if(rc == LIBSSH2_ERROR_EAGAIN)
            return rc;
        else if(rc) {
            return _libssh2_error(session, rc,
                                  "Failed sending banner");
        }
        session->startup_state = libssh2_NB_state_sent;
        session->banner_TxRx_state = libssh2_NB_state_idle;
    }

    if(session->startup_state == libssh2_NB_state_sent) {
        do {
            rc = banner_receive(session);
            if(rc == LIBSSH2_ERROR_EAGAIN)
                return rc;
            else if(rc)
                return _libssh2_error(session, rc,
                                      "Failed getting banner");
        } while(strncmp("SSH-", (const char *)session->remote.banner, 4));

        session->startup_state = libssh2_NB_state_sent1;
    }

    if(session->startup_state == libssh2_NB_state_sent1) {
        rc = _libssh2_kex_exchange(session, 0, &session->startup_key_state);
        if(rc == LIBSSH2_ERROR_EAGAIN)
            return rc;
        else if(rc)
            return _libssh2_error(session, rc,
                                  "Unable to exchange encryption keys");

        session->startup_state = libssh2_NB_state_sent2;
    }

    if(session->startup_state == libssh2_NB_state_sent2) {
        _libssh2_debug((session, LIBSSH2_TRACE_TRANS,
                       "Requesting userauth service"));

        /* Request the userauth service */
        session->startup_service[0] = SSH_MSG_SERVICE_REQUEST;
        _libssh2_htonu32(session->startup_service + 1,
                         sizeof("ssh-userauth") - 1);
        memcpy(session->startup_service + 5, "ssh-userauth",
               sizeof("ssh-userauth") - 1);

        session->startup_state = libssh2_NB_state_sent3;
    }

    if(session->startup_state == libssh2_NB_state_sent3) {
        rc = _libssh2_transport_send(session, session->startup_service,
                                     sizeof("ssh-userauth") + 5 - 1,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN)
            return rc;
        else if(rc) {
            return _libssh2_error(session, rc,
                                  "Unable to ask for ssh-userauth service");
        }

        session->startup_state = libssh2_NB_state_sent4;
    }

    if(session->startup_state == libssh2_NB_state_sent4) {
        rc = _libssh2_packet_require(session, SSH_MSG_SERVICE_ACCEPT,
                                     &session->startup_data,
                                     &session->startup_data_len, 0, NULL, 0,
                                     &session->startup_req_state);
        if(rc)
            return _libssh2_error(session, rc,
                                  "Failed to get response to "
                                  "ssh-userauth request");

        if(session->startup_data_len < 5) {
            return _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                                  "Unexpected packet length");
        }

        session->startup_service_length =
            _libssh2_ntohu32(session->startup_data + 1);


        if((session->startup_service_length != (sizeof("ssh-userauth") - 1))
            || strncmp("ssh-userauth",
                       (const char *) session->startup_data + 5,
                       session->startup_service_length)) {
            LIBSSH2_FREE(session, session->startup_data);
            session->startup_data = NULL;
            return _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                                  "Invalid response received from server");
        }
        LIBSSH2_FREE(session, session->startup_data);
        session->startup_data = NULL;

        session->startup_state = libssh2_NB_state_idle;

        return 0;
    }

    /* just for safety return some error */
    return LIBSSH2_ERROR_INVAL;
}

/*
 * libssh2_session_handshake
 *
 * session: LIBSSH2_SESSION struct allocated and owned by the calling program
 * sock:    *must* be populated with an opened and connected socket.
 *
 * Returns: 0 on success, or non-zero on failure
 */
LIBSSH2_API int
libssh2_session_handshake(LIBSSH2_SESSION *session, libssh2_socket_t sock)
{
    int rc;

    BLOCK_ADJUST(rc, session, session_startup(session, sock));

    return rc;
}

/*
 * libssh2_session_startup
 *
 * DEPRECATED. Use libssh2_session_handshake() instead! This function is not
 * portable enough.
 *
 * session: LIBSSH2_SESSION struct allocated and owned by the calling program
 * sock:    *must* be populated with an opened and connected socket.
 *
 * Returns: 0 on success, or non-zero on failure
 */
LIBSSH2_API int
libssh2_session_startup(LIBSSH2_SESSION *session, int sock)
{
    return libssh2_session_handshake(session, (libssh2_socket_t) sock);
}

/*
 * session_free
 *
 * Frees the memory allocated to the session
 * Also closes and frees any channels attached to this session
 */
static int
session_free(LIBSSH2_SESSION *session)
{
    int rc;
    LIBSSH2_PACKET *pkg;
    LIBSSH2_CHANNEL *ch;
    LIBSSH2_LISTENER *l;
    int packets_left = 0;

    if(session->free_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_TRANS,
                       "Freeing session resource",
                       session->remote.banner));

        session->free_state = libssh2_NB_state_created;
    }

    if(session->free_state == libssh2_NB_state_created) {
        /* !checksrc! disable EQUALSNULL 1 */
        while((ch = _libssh2_list_first(&session->channels)) != NULL) {
            rc = _libssh2_channel_free(ch);
            if(rc == LIBSSH2_ERROR_EAGAIN)
                return rc;
        }

        session->free_state = libssh2_NB_state_sent;
    }

    if(session->free_state == libssh2_NB_state_sent) {
        /* !checksrc! disable EQUALSNULL 1 */
        while((l = _libssh2_list_first(&session->listeners)) != NULL) {
            rc = _libssh2_channel_forward_cancel(l);
            if(rc == LIBSSH2_ERROR_EAGAIN)
                return rc;
        }

        session->free_state = libssh2_NB_state_sent1;
    }

    if(session->state & LIBSSH2_STATE_NEWKEYS) {
        /* hostkey */
        if(session->hostkey && session->hostkey->dtor) {
            session->hostkey->dtor(session, &session->server_hostkey_abstract);
        }

        /* Client to Server */
        /* crypt */
        if(session->local.crypt && session->local.crypt->dtor) {
            session->local.crypt->dtor(session,
                                       &session->local.crypt_abstract);
        }
        /* comp */
        if(session->local.comp && session->local.comp->dtor) {
            session->local.comp->dtor(session, 1,
                                      &session->local.comp_abstract);
        }
        /* mac */
        if(session->local.mac && session->local.mac->dtor) {
            session->local.mac->dtor(session, &session->local.mac_abstract);
        }

        /* Server to Client */
        /* crypt */
        if(session->remote.crypt && session->remote.crypt->dtor) {
            session->remote.crypt->dtor(session,
                                        &session->remote.crypt_abstract);
        }
        /* comp */
        if(session->remote.comp && session->remote.comp->dtor) {
            session->remote.comp->dtor(session, 0,
                                       &session->remote.comp_abstract);
        }
        /* mac */
        if(session->remote.mac && session->remote.mac->dtor) {
            session->remote.mac->dtor(session, &session->remote.mac_abstract);
        }

        /* session_id */
        if(session->session_id) {
            LIBSSH2_FREE(session, session->session_id);
        }
    }

    /* Free banner(s) */
    if(session->remote.banner) {
        LIBSSH2_FREE(session, session->remote.banner);
    }
    if(session->local.banner) {
        LIBSSH2_FREE(session, session->local.banner);
    }

    /* Free preference(s) */
    if(session->kex_prefs) {
        LIBSSH2_FREE(session, session->kex_prefs);
    }
    if(session->hostkey_prefs) {
        LIBSSH2_FREE(session, session->hostkey_prefs);
    }

    if(session->local.kexinit) {
        LIBSSH2_FREE(session, session->local.kexinit);
    }
    if(session->local.crypt_prefs) {
        LIBSSH2_FREE(session, session->local.crypt_prefs);
    }
    if(session->local.mac_prefs) {
        LIBSSH2_FREE(session, session->local.mac_prefs);
    }
    if(session->local.comp_prefs) {
        LIBSSH2_FREE(session, session->local.comp_prefs);
    }
    if(session->local.lang_prefs) {
        LIBSSH2_FREE(session, session->local.lang_prefs);
    }

    if(session->remote.kexinit) {
        LIBSSH2_FREE(session, session->remote.kexinit);
    }
    if(session->remote.crypt_prefs) {
        LIBSSH2_FREE(session, session->remote.crypt_prefs);
    }
    if(session->remote.mac_prefs) {
        LIBSSH2_FREE(session, session->remote.mac_prefs);
    }
    if(session->remote.comp_prefs) {
        LIBSSH2_FREE(session, session->remote.comp_prefs);
    }
    if(session->remote.lang_prefs) {
        LIBSSH2_FREE(session, session->remote.lang_prefs);
    }
    if(session->server_sign_algorithms) {
        LIBSSH2_FREE(session, session->server_sign_algorithms);
    }
    if(session->sign_algo_prefs) {
        LIBSSH2_FREE(session, session->sign_algo_prefs);
    }

    /*
     * Make sure all memory used in the state variables are free
     */
    if(session->kexinit_data) {
        LIBSSH2_FREE(session, session->kexinit_data);
    }
    if(session->startup_data) {
        LIBSSH2_FREE(session, session->startup_data);