niceSOFT/libssh | Gitverse

src/client.c
779 строк23 KB
Jakub Jelen
client: Properly indicate fall through
05 май 2020, 15:33
05 май 2020, 15:33b93c9ae
/*
 * client.c - SSH client 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 <stdio.h>

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

#include "libssh/priv.h"
#include "libssh/ssh2.h"
#include "libssh/buffer.h"
#include "libssh/packet.h"
#include "libssh/options.h"
#include "libssh/socket.h"
#include "libssh/session.h"
#include "libssh/dh.h"
#ifdef WITH_GEX
#include "libssh/dh-gex.h"
#endif /* WITH_GEX */
#include "libssh/ecdh.h"
#include "libssh/threads.h"
#include "libssh/misc.h"
#include "libssh/pki.h"
#include "libssh/kex.h"

#define set_status(session, status) do {\
        if (session->common.callbacks && session->common.callbacks->connect_status_function) \
            session->common.callbacks->connect_status_function(session->common.callbacks->userdata, status); \
    } while (0)

/**
 * @internal
 * @brief Callback to be called when the socket is connected or had a
 * connection error. Changes the state of the session and updates the error
 * message.
 * @param code one of SSH_SOCKET_CONNECTED_OK or SSH_SOCKET_CONNECTED_ERROR
 * @param user is a pointer to session
 */
static void socket_callback_connected(int code, int errno_code, void *user){
	ssh_session session=(ssh_session)user;

	if (session->session_state != SSH_SESSION_STATE_CONNECTING &&
	    session->session_state != SSH_SESSION_STATE_SOCKET_CONNECTED)
	{
		ssh_set_error(session,SSH_FATAL, "Wrong state in socket_callback_connected : %d",
				session->session_state);

		return;
	}

	SSH_LOG(SSH_LOG_RARE,"Socket connection callback: %d (%d)",code, errno_code);
	if(code == SSH_SOCKET_CONNECTED_OK)
		session->session_state=SSH_SESSION_STATE_SOCKET_CONNECTED;
	else {
		session->session_state=SSH_SESSION_STATE_ERROR;
		ssh_set_error(session,SSH_FATAL,"%s",strerror(errno_code));
	}
	session->ssh_connection_callback(session);
}

/**
 * @internal
 *
 * @brief Gets the banner from socket and saves it in session.
 * Updates the session state
 *
 * @param  data pointer to the beginning of header
 * @param  len size of the banner
 * @param  user is a pointer to session
 * @returns Number of bytes processed, or zero if the banner is not complete.
 */
static int callback_receive_banner(const void *data, size_t len, void *user)
{
    char *buffer = (char *)data;
    ssh_session session=(ssh_session) user;
    char *str = NULL;
    size_t i;
    int ret=0;

    if (session->session_state != SSH_SESSION_STATE_SOCKET_CONNECTED) {
        ssh_set_error(session,SSH_FATAL,
                      "Wrong state in callback_receive_banner : %d",
                      session->session_state);

        return SSH_ERROR;
    }
    for (i = 0; i < len; ++i) {
#ifdef WITH_PCAP
        if (session->pcap_ctx && buffer[i] == '\n') {
            ssh_pcap_context_write(session->pcap_ctx,
                                   SSH_PCAP_DIR_IN,
                                   buffer,i+1,
                                   i+1);
        }
#endif
        if (buffer[i] == '\r') {
            buffer[i] = '\0';
        }
        if (buffer[i] == '\n') {
            int cmp;

            buffer[i] = '\0';

            /* The server MAY send other lines of data... */
            cmp = strncmp(buffer, "SSH-", 4);
            if (cmp == 0) {
                str = strdup(buffer);
                if (str == NULL) {
                    return SSH_ERROR;
                }
                /* number of bytes read */
                ret = i + 1;
                session->serverbanner = str;
                session->session_state = SSH_SESSION_STATE_BANNER_RECEIVED;
                SSH_LOG(SSH_LOG_PACKET, "Received banner: %s", str);
                session->ssh_connection_callback(session);

                return ret;
            } else {
                SSH_LOG(SSH_LOG_DEBUG,
                        "ssh_protocol_version_exchange: %s",
                        buffer);
                ret = i + 1;
                break;
            }
        }
        /* According to RFC 4253 the max banner length is 255 */
        if (i > 255) {
            /* Too big banner */
            session->session_state=SSH_SESSION_STATE_ERROR;
            ssh_set_error(session,
                          SSH_FATAL,
                          "Receiving banner: too large banner");

            return 0;
        }
    }

    return ret;
}

/** @internal
 * @brief Sends a SSH banner to the server.
 *
 * @param session      The SSH session to use.
 *
 * @param server       Send client or server banner.
 *
 * @return 0 on success, < 0 on error.
 */
int ssh_send_banner(ssh_session session, int server)
{
    const char *banner = CLIENT_BANNER_SSH2;
    const char *terminator = "\r\n";
    /* The maximum banner length is 255 for SSH2 */
    char buffer[256] = {0};
    size_t len;
    int rc = SSH_ERROR;

    if (server == 1) {
        if (session->opts.custombanner == NULL){
            session->serverbanner = strdup(banner);
            if (session->serverbanner == NULL) {
                goto end;
            }
        } else {
            len = strlen(session->opts.custombanner);
            session->serverbanner = malloc(len + 8 + 1);
            if(session->serverbanner == NULL) {
                goto end;
            }
            snprintf(session->serverbanner,
                     len + 8 + 1,
                     "SSH-2.0-%s",
                     session->opts.custombanner);
        }

        snprintf(buffer,
                 sizeof(buffer),
                 "%s%s",
                 session->serverbanner,
                 terminator);
    } else {
        session->clientbanner = strdup(banner);
        if (session->clientbanner == NULL) {
            goto end;
        }

        snprintf(buffer,
                 sizeof(buffer),
                 "%s%s",
                 session->clientbanner,
                 terminator);
    }

    rc = ssh_socket_write(session->socket, buffer, strlen(buffer));
    if (rc == SSH_ERROR) {
        goto end;
    }
#ifdef WITH_PCAP
    if (session->pcap_ctx != NULL) {
        ssh_pcap_context_write(session->pcap_ctx,
                               SSH_PCAP_DIR_OUT,
                               buffer,
                               strlen(buffer),
                               strlen(buffer));
    }
#endif

    rc = SSH_OK;
end:
    return rc;
}

/** @internal
 * @brief launches the DH handshake state machine
 * @param session session handle
 * @returns SSH_OK or SSH_ERROR
 * @warning this function returning is no proof that DH handshake is
 * completed
 */
static int dh_handshake(ssh_session session) {

  int rc = SSH_AGAIN;

  switch (session->dh_handshake_state) {
    case DH_STATE_INIT:
      switch(session->next_crypto->kex_type){
        case SSH_KEX_DH_GROUP1_SHA1:
        case SSH_KEX_DH_GROUP14_SHA1:
        case SSH_KEX_DH_GROUP14_SHA256:
        case SSH_KEX_DH_GROUP16_SHA512:
        case SSH_KEX_DH_GROUP18_SHA512:
          rc = ssh_client_dh_init(session);
          break;
#ifdef WITH_GEX
        case SSH_KEX_DH_GEX_SHA1:
        case SSH_KEX_DH_GEX_SHA256:
          rc = ssh_client_dhgex_init(session);
          break;
#endif /* WITH_GEX */
#ifdef HAVE_ECDH
        case SSH_KEX_ECDH_SHA2_NISTP256:
        case SSH_KEX_ECDH_SHA2_NISTP384:
        case SSH_KEX_ECDH_SHA2_NISTP521:
          rc = ssh_client_ecdh_init(session);
          break;
#endif
#ifdef HAVE_CURVE25519
        case SSH_KEX_CURVE25519_SHA256:
        case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
          rc = ssh_client_curve25519_init(session);
          break;
#endif
        default:
          rc = SSH_ERROR;
      }

      break;
    case DH_STATE_INIT_SENT:
    	/* wait until ssh_packet_dh_reply is called */
    	break;
    case DH_STATE_NEWKEYS_SENT:
    	/* wait until ssh_packet_newkeys is called */
    	break;
    case DH_STATE_FINISHED:
      return SSH_OK;
    default:
      ssh_set_error(session, SSH_FATAL, "Invalid state in dh_handshake(): %d",
          session->dh_handshake_state);

      return SSH_ERROR;
  }

  return rc;
}

static int ssh_service_request_termination(void *s){
  ssh_session session = (ssh_session)s;
  if(session->session_state == SSH_SESSION_STATE_ERROR ||
      session->auth.service_state != SSH_AUTH_SERVICE_SENT)
    return 1;
  else
    return 0;
}

/**
 * @internal
 *
 * @brief Request a service from the SSH server.
 *
 * Service requests are for example: ssh-userauth, ssh-connection, etc.
 *
 * @param  session      The session to use to ask for a service request.
 * @param  service      The service request.
 *
 * @return SSH_OK on success
 * @return SSH_ERROR on error
 * @return SSH_AGAIN No response received yet
 * @bug actually only works with ssh-userauth
 */
int ssh_service_request(ssh_session session, const char *service) {
  int rc=SSH_ERROR;

  if(session->auth.service_state != SSH_AUTH_SERVICE_NONE)
    goto pending;

  rc = ssh_buffer_pack(session->out_buffer,
                       "bs",
                       SSH2_MSG_SERVICE_REQUEST,
                       service);
  if (rc != SSH_OK){
      ssh_set_error_oom(session);
      return SSH_ERROR;
  }
  session->auth.service_state = SSH_AUTH_SERVICE_SENT;
  if (ssh_packet_send(session) == SSH_ERROR) {
    ssh_set_error(session, SSH_FATAL,
        "Sending SSH2_MSG_SERVICE_REQUEST failed.");
      return SSH_ERROR;
  }

  SSH_LOG(SSH_LOG_PACKET,
      "Sent SSH_MSG_SERVICE_REQUEST (service %s)", service);
pending:
  rc=ssh_handle_packets_termination(session,SSH_TIMEOUT_USER,
      ssh_service_request_termination, session);
  if (rc == SSH_ERROR) {
      return SSH_ERROR;
  }
  switch(session->auth.service_state) {
  case SSH_AUTH_SERVICE_DENIED:
    ssh_set_error(session,SSH_FATAL,"ssh_auth_service request denied");
    break;
  case SSH_AUTH_SERVICE_ACCEPTED:
    rc=SSH_OK;
    break;
  case SSH_AUTH_SERVICE_SENT:
    rc=SSH_AGAIN;
    break;
  case SSH_AUTH_SERVICE_NONE:
    rc=SSH_ERROR;
    break;
  }

  return rc;
}

/**
 * @addtogroup libssh_session
 *
 * @{
 */

/**
 * @internal
 *
 * @brief A function to be called each time a step has been done in the
 * connection.
 */
static void ssh_client_connection_callback(ssh_session session)
{
    int rc;

    switch(session->session_state) {
        case SSH_SESSION_STATE_NONE:
        case SSH_SESSION_STATE_CONNECTING:
            break;
        case SSH_SESSION_STATE_SOCKET_CONNECTED:
            ssh_set_fd_towrite(session);
            ssh_send_banner(session, 0);

            break;
        case SSH_SESSION_STATE_BANNER_RECEIVED:
            if (session->serverbanner == NULL) {
                goto error;
            }
            set_status(session, 0.4f);
            SSH_LOG(SSH_LOG_PROTOCOL,
                    "SSH server banner: %s", session->serverbanner);

            /* Here we analyze the different protocols the server allows. */
            rc = ssh_analyze_banner(session, 0);
            if (rc < 0) {
                ssh_set_error(session, SSH_FATAL,
                        "No version of SSH protocol usable (banner: %s)",
                        session->serverbanner);
                goto error;
            }

            ssh_packet_register_socket_callback(session, session->socket);

            ssh_packet_set_default_callbacks(session);
            session->session_state = SSH_SESSION_STATE_INITIAL_KEX;
            rc = ssh_set_client_kex(session);
            if (rc != SSH_OK) {
                goto error;
            }
            rc = ssh_send_kex(session, 0);
            if (rc < 0) {
                goto error;
            }
            set_status(session, 0.5f);

            break;
        case SSH_SESSION_STATE_INITIAL_KEX:
            /* TODO: This state should disappear in favor of get_key handle */
            break;
        case SSH_SESSION_STATE_KEXINIT_RECEIVED:
            set_status(session,0.6f);
            ssh_list_kex(&session->next_crypto->server_kex);
            if (session->next_crypto->client_kex.methods[0] == NULL) {
                /* in rekeying state if next_crypto client_kex is empty */
                rc = ssh_set_client_kex(session);
                if (rc != SSH_OK) {
                    goto error;
                }
                rc = ssh_send_kex(session, 0);
                if (rc < 0) {
                    goto error;
                }
            }
            if (ssh_kex_select_methods(session) == SSH_ERROR)
                goto error;
            set_status(session,0.8f);
            session->session_state=SSH_SESSION_STATE_DH;
            if (dh_handshake(session) == SSH_ERROR) {
                goto error;
            }
            FALL_THROUGH;
        case SSH_SESSION_STATE_DH:
            if(session->dh_handshake_state==DH_STATE_FINISHED){
                set_status(session,1.0f);
                session->connected = 1;
                if (session->flags & SSH_SESSION_FLAG_AUTHENTICATED)
                    session->session_state = SSH_SESSION_STATE_AUTHENTICATED;
                else
                    session->session_state=SSH_SESSION_STATE_AUTHENTICATING;
            }
            break;
        case SSH_SESSION_STATE_AUTHENTICATING:
            break;
        case SSH_SESSION_STATE_ERROR:
            goto error;
        default:
            ssh_set_error(session,SSH_FATAL,"Invalid state %d",session->session_state);
    }

    return;
error:
    ssh_socket_close(session->socket);
    session->alive = 0;
    session->session_state=SSH_SESSION_STATE_ERROR;

}

/** @internal
 * @brief describe under which conditions the ssh_connect function may stop
 */
static int ssh_connect_termination(void *user){
  ssh_session session = (ssh_session)user;
  switch(session->session_state){
    case SSH_SESSION_STATE_ERROR:
    case SSH_SESSION_STATE_AUTHENTICATING:
    case SSH_SESSION_STATE_DISCONNECTED:
      return 1;
    default:
      return 0;
  }
}

/**
 * @brief Connect to the ssh server.
 *
 * @param[in]  session  The ssh session to connect.
 *
 * @returns             SSH_OK on success, SSH_ERROR on error.
 * @returns             SSH_AGAIN, if the session is in nonblocking mode,
 *                      and call must be done again.
 *
 * @see ssh_new()
 * @see ssh_disconnect()
 */
int ssh_connect(ssh_session session)
{
    int ret;

    if (!is_ssh_initialized()) {
        ssh_set_error(session, SSH_FATAL,
                      "Library not initialized.");

        return SSH_ERROR;
    }

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

    switch(session->pending_call_state) {
    case SSH_PENDING_CALL_NONE:
        break;
    case SSH_PENDING_CALL_CONNECT:
        goto pending;
    default:
        ssh_set_error(session, SSH_FATAL,
                      "Bad call during pending SSH call in ssh_connect");

        return SSH_ERROR;
    }
    session->alive = 0;
    session->client = 1;

    if (session->opts.fd == SSH_INVALID_SOCKET &&
        session->opts.host == NULL &&
        session->opts.ProxyCommand == NULL)
    {
        ssh_set_error(session, SSH_FATAL, "Hostname required");
        return SSH_ERROR;
    }

    /* If the system configuration files were not yet processed, do it now */
    if (!session->opts.config_processed) {
        ret = ssh_options_parse_config(session, NULL);
        if (ret != 0) {
            ssh_set_error(session, SSH_FATAL,
                          "Failed to process system configuration files");
            return SSH_ERROR;
        }
    }

    ret = ssh_options_apply(session);
    if (ret < 0) {
        ssh_set_error(session, SSH_FATAL, "Couldn't apply options");
        return SSH_ERROR;
    }

    SSH_LOG(SSH_LOG_PROTOCOL,
            "libssh %s, using threading %s",
            ssh_copyright(),
            ssh_threads_get_type());

    session->ssh_connection_callback = ssh_client_connection_callback;
    session->session_state = SSH_SESSION_STATE_CONNECTING;
    ssh_socket_set_callbacks(session->socket, &session->socket_callbacks);
    session->socket_callbacks.connected = socket_callback_connected;
    session->socket_callbacks.data = callback_receive_banner;
    session->socket_callbacks.exception = ssh_socket_exception_callback;
    session->socket_callbacks.userdata = session;

    if (session->opts.fd != SSH_INVALID_SOCKET) {
        session->session_state = SSH_SESSION_STATE_SOCKET_CONNECTED;
        ssh_socket_set_fd(session->socket, session->opts.fd);
        ret = SSH_OK;
#ifndef _WIN32
    } else if (session->opts.ProxyCommand != NULL) {
        ret = ssh_socket_connect_proxycommand(session->socket,
                session->opts.ProxyCommand);
#endif
    } else {
        ret = ssh_socket_connect(session->socket,
                                 session->opts.host,
                                 session->opts.port > 0 ? session->opts.port : 22,
                                 session->opts.bindaddr);
    }
    if (ret == SSH_ERROR) {
        return SSH_ERROR;
    }

    set_status(session, 0.2f);

    session->alive = 1;
    SSH_LOG(SSH_LOG_PROTOCOL,
            "Socket connecting, now waiting for the callbacks to work");

pending:
    session->pending_call_state = SSH_PENDING_CALL_CONNECT;
    if(ssh_is_blocking(session)) {
        int timeout = (session->opts.timeout * 1000) +
            (session->opts.timeout_usec / 1000);
        if (timeout == 0) {
            timeout = 10 * 1000;
        }
        SSH_LOG(SSH_LOG_PACKET, "Actual timeout : %d", timeout);
        ret = ssh_handle_packets_termination(session, timeout,
                                             ssh_connect_termination, session);
        if (session->session_state != SSH_SESSION_STATE_ERROR &&
            (ret == SSH_ERROR || !ssh_connect_termination(session)))
        {
            ssh_set_error(session, SSH_FATAL,
                          "Timeout connecting to %s", session->opts.host);
            session->session_state = SSH_SESSION_STATE_ERROR;
        }
    } else {
        ret = ssh_handle_packets_termination(session,
                                             SSH_TIMEOUT_NONBLOCKING,
                                             ssh_connect_termination,
                                             session);
        if (ret == SSH_ERROR) {
            session->session_state = SSH_SESSION_STATE_ERROR;
        }
    }

    SSH_LOG(SSH_LOG_PACKET, "current state : %d", session->session_state);
    if (!ssh_is_blocking(session) && !ssh_connect_termination(session)) {
        return SSH_AGAIN;
    }

    session->pending_call_state = SSH_PENDING_CALL_NONE;
    if (session->session_state == SSH_SESSION_STATE_ERROR ||
        session->session_state == SSH_SESSION_STATE_DISCONNECTED)
    {
        return SSH_ERROR;
    }

    return SSH_OK;
}

/**
 * @brief Get the issue banner from the server.
 *
 * This is the banner showing a disclaimer to users who log in,
 * typically their right or the fact that they will be monitored.
 *
 * @param[in]  session  The SSH session to use.
 *
 * @return A newly allocated string with the banner, NULL on error.
 */
char *ssh_get_issue_banner(ssh_session session) {
  if (session == NULL || session->banner == NULL) {
    return NULL;
  }

  return ssh_string_to_char(session->banner);
}

/**
 * @brief Get the version of the OpenSSH server, if it is not an OpenSSH server
 * then 0 will be returned.
 *
 * You can use the SSH_VERSION_INT macro to compare version numbers.
 *
 * @param[in]  session  The SSH session to use.
 *
 * @return The version number if available, 0 otherwise.
 *
 * @code
 * int openssh = ssh_get_openssh_version();
 *
 * if (openssh == SSH_INT_VERSION(6, 1, 0)) {
 *     printf("Version match!\m");
 * }
 * @endcode
 */
int ssh_get_openssh_version(ssh_session session) {
  if (session == NULL) {
    return 0;
  }

  return session->openssh;
}

/**
 * @brief Disconnect from a session (client or server).
 * The session can then be reused to open a new session.
 *
 * @param[in]  session  The SSH session to use.
 */
void ssh_disconnect(ssh_session session) {
  struct ssh_iterator *it;
  int rc;

  if (session == NULL) {
    return;
  }

  if (session->socket != NULL && ssh_socket_is_open(session->socket)) {
    rc = ssh_buffer_pack(session->out_buffer,
                         "bdss",
                         SSH2_MSG_DISCONNECT,
                         SSH2_DISCONNECT_BY_APPLICATION,
                         "Bye Bye",
                         ""); /* language tag */
    if (rc != SSH_OK){
      ssh_set_error_oom(session);
      goto error;
    }

    ssh_packet_send(session);
    ssh_socket_close(session->socket);
  }
error:
  session->recv_seq = 0;
  session->send_seq = 0;
  session->alive = 0;
  if (session->socket != NULL){
    ssh_socket_reset(session->socket);
  }
  session->opts.fd = SSH_INVALID_SOCKET;
  session->session_state=SSH_SESSION_STATE_DISCONNECTED;

  while ((it=ssh_list_get_iterator(session->channels)) != NULL) {
    ssh_channel_do_free(ssh_iterator_value(ssh_channel,it));
    ssh_list_remove(session->channels, it);
  }
  if(session->current_crypto){
    crypto_free(session->current_crypto);
    session->current_crypto=NULL;
  }
  if (session->next_crypto) {
    crypto_free(session->next_crypto);
    session->next_crypto = crypto_new();
    if (session->next_crypto == NULL) {
      ssh_set_error_oom(session);
    }
  }
  if (session->in_buffer) {
    ssh_buffer_reinit(session->in_buffer);
  }
  if (session->out_buffer) {
    ssh_buffer_reinit(session->out_buffer);
  }
  if (session->in_hashbuf) {
    ssh_buffer_reinit(session->in_hashbuf);
  }
  if (session->out_hashbuf) {
    ssh_buffer_reinit(session->out_hashbuf);
  }
  session->auth.supported_methods = 0;
  SAFE_FREE(session->serverbanner);
  SAFE_FREE(session->clientbanner);

  if(session->ssh_message_list){
    ssh_message msg;
    while((msg=ssh_list_pop_head(ssh_message ,session->ssh_message_list))
        != NULL){
      ssh_message_free(msg);
    }
    ssh_list_free(session->ssh_message_list);
    session->ssh_message_list=NULL;
  }

  if (session->packet_callbacks){
    ssh_list_free(session->packet_callbacks);
    session->packet_callbacks=NULL;
  }
}

const char *ssh_copyright(void) {
    return SSH_STRINGIFY(LIBSSH_VERSION) " (c) 2003-2019 "
           "Aris Adamantiadis, Andreas Schneider "
           "and libssh contributors. "
           "Distributed under the LGPL, please refer to COPYING "
           "file for information about your rights";
}
/** @} */