GUACAMOLE-312: Implement VNC protocol support for SSH tunneling.

src/protocols/vnc/client.c

@@ -26,6 +26,7 @@
 #ifdef ENABLE_COMMON_SSH
 #include "common-ssh/sftp.h"
 #include "common-ssh/ssh.h"
+#include "common-ssh/tunnel.h"
 #include "common-ssh/user.h"
 #endif
 
@@ -120,6 +121,10 @@ int guac_client_init(guac_client* client) {
     client->leave_handler = guac_vnc_user_leave_handler;
     client->free_handler = guac_vnc_client_free_handler;
 
+#ifdef ENABLE_COMMON_SSH
+    guac_common_ssh_init(client);
+#endif
+
     return 0;
 }
 
@@ -179,6 +184,9 @@ int guac_vnc_client_free_handler(guac_client* client) {
     if (vnc_client->sftp_user)
         guac_common_ssh_destroy_user(vnc_client->sftp_user);
 
+    if (vnc_client->ssh_tunnel)
+        guac_common_ssh_tunnel_cleanup(vnc_client->ssh_tunnel);
+
     guac_common_ssh_uninit();
 #endif
 

src/protocols/vnc/settings.c

@@ -22,6 +22,7 @@
 #include "argv.h"
 #include "client.h"
 #include "common/defaults.h"
+#include "common-ssh/ssh-constants.h"
 #include "settings.h"
 
 #include <guacamole/mem.h>
@@ -76,6 +77,15 @@ const char* GUAC_VNC_CLIENT_ARGS[] = {
     "sftp-server-alive-interval",
     "sftp-disable-download",
     "sftp-disable-upload",
+    "ssh-tunnel",
+    "ssh-tunnel-host",
+    "ssh-tunnel-port",
+    "ssh-tunnel-host-key",
+    "ssh-tunnel-username",
+    "ssh-tunnel-password",
+    "ssh-tunnel-private-key",
+    "ssh-tunnel-passphrase",
+    "ssh-tunnel-alive-interval",
 #endif
 
     "recording-path",
@@ -289,6 +299,55 @@ enum VNC_ARGS_IDX {
      * "false" or not set, file uploads will be allowed.
      */
     IDX_SFTP_DISABLE_UPLOAD,
+
+    /**
+     * True if SSH tunneling should be enabled. If false or not set, SSH
+     * tunneling will not be used.
+     */
+    IDX_SSH_TUNNEL,
+
+    /**
+     * The hostname or IP address of the SSH server to use for tunneling.
+     */
+    IDX_SSH_TUNNEL_HOST,
+
+    /**
+     * The TCP port of the SSH server to use for tunneling.
+     */
+    IDX_SSH_TUNNEL_PORT,
+
+    /**
+     * If host key checking should be done, the public key of the SSH host
+     * to be used for tunneling.
+     */
+    IDX_SSH_TUNNEL_HOST_KEY,
+
+    /**
+     * The username for authenticating to the SSH hsot for tunneling.
+     */
+    IDX_SSH_TUNNEL_USERNAME,
+
+    /**
+     * The password to use to authenticate to the SSH host for tunneling.
+     */
+    IDX_SSH_TUNNEL_PASSWORD,
+
+    /**
+     * The private key to use to authenticate to the SSH host for tunneling,
+     * as an alternative to password-based authentication.
+     */
+    IDX_SSH_TUNNEL_PRIVATE_KEY,
+
+    /**
+     * The passphrase to use to decrypt the private key.
+     */
+    IDX_SSH_TUNNEL_PASSPHRASE,
+
+    /**
+     * The interval at which keepalive packets should be sent to the SSH
+     * tunneling server, or zero if keepalive should be disabled.
+     */
+    IDX_SSH_TUNNEL_ALIVE_INTERVAL,
 #endif
 
     /**
@@ -591,12 +650,13 @@ guac_vnc_settings* guac_vnc_parse_args(guac_user* user,
     /* SFTP root directory */
     settings->sftp_root_directory =
         guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
-                IDX_SFTP_ROOT_DIRECTORY, "/");
+                IDX_SFTP_ROOT_DIRECTORY, GUAC_COMMON_SSH_SFTP_DEFAULT_ROOT);
 
     /* Default keepalive value */
     settings->sftp_server_alive_interval =
         guac_user_parse_args_int(user, GUAC_VNC_CLIENT_ARGS, argv,
-                IDX_SFTP_SERVER_ALIVE_INTERVAL, 0);
+                IDX_SFTP_SERVER_ALIVE_INTERVAL,
+                GUAC_COMMON_SSH_DEFAULT_ALIVE_INTERVAL);
 
     settings->sftp_disable_download =
         guac_user_parse_args_boolean(user, GUAC_VNC_CLIENT_ARGS, argv,
@@ -605,6 +665,49 @@ guac_vnc_settings* guac_vnc_parse_args(guac_user* user,
     settings->sftp_disable_upload =
         guac_user_parse_args_boolean(user, GUAC_VNC_CLIENT_ARGS, argv,
                 IDX_SFTP_DISABLE_UPLOAD, false);
+
+    /* Parse SSH tunneling settings. */
+    settings->ssh_tunnel =
+        guac_user_parse_args_boolean(user, GUAC_VNC_CLIENT_ARGS, argv,
+                IDX_SSH_TUNNEL, false);
+
+    /* Only parse remaining tunneling settings if it has been enabled. */
+    if (settings->ssh_tunnel) {
+
+        settings->ssh_tunnel_host =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_HOST, NULL);
+
+        settings->ssh_tunnel_port =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_PORT, GUAC_COMMON_SSH_DEFAULT_PORT);
+
+        settings->ssh_tunnel_host_key =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_HOST_KEY, NULL);
+
+        settings->ssh_tunnel_username =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_USERNAME, NULL);
+
+        settings->ssh_tunnel_password =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_PASSWORD, NULL);
+
+        settings->ssh_tunnel_private_key =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_PRIVATE_KEY, NULL);
+
+        settings->ssh_tunnel_passphrase =
+            guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_PASSPHRASE, NULL);
+
+        settings->ssh_tunnel_alive_interval =
+            guac_user_parse_args_int(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SSH_TUNNEL_ALIVE_INTERVAL,
+                    GUAC_COMMON_SSH_DEFAULT_ALIVE_INTERVAL);
+
+    }
 #endif
 
     /* Read recording path */
@@ -719,6 +822,13 @@ void guac_vnc_settings_free(guac_vnc_settings* settings) {
     guac_mem_free(settings->sftp_port);
     guac_mem_free(settings->sftp_private_key);
     guac_mem_free(settings->sftp_username);
+    guac_mem_free(settings->ssh_tunnel_host);
+    guac_mem_free(settings->ssh_tunnel_host_key);
+    guac_mem_free(settings->ssh_tunnel_port);
+    guac_mem_free(settings->ssh_tunnel_username);
+    guac_mem_free(settings->ssh_tunnel_password);
+    guac_mem_free(settings->ssh_tunnel_private_key);
+    guac_mem_free(settings->ssh_tunnel_passphrase);
 #endif
 
 #ifdef ENABLE_PULSE

src/protocols/vnc/settings.h

@@ -240,6 +240,69 @@ typedef struct guac_vnc_settings {
      * to "false" or not set, file uploads will be allowed.
      */
     bool sftp_disable_upload;
+
+    /**
+     * Whether to enable tunneling of this connection through the specified
+     * SSH server. If set to "true", guacd will attempt to connect to the SSH
+     * server and tunnel all of the traffic through the SSH connection. If
+     * set to "false" or not set, SSH tunneling will not be used.
+     */
+    bool ssh_tunnel;
+
+    /**
+     * The hostname or address of the host through which traffic should be
+     * tunneled over SSH. If tunneling is enabled, this is required, or the
+     * connection will be aborted.
+     */
+    char* ssh_tunnel_host;
+
+    /**
+     * The port on which to connect to the SSH server to tunnel traffic, if
+     * SSH tunneling is enabled. If not specified, this will default to 22, the
+     * normal SSH port.
+     */
+    char* ssh_tunnel_port;
+
+    /**
+     * The public key of the SSH host through which this connection will be
+     * tunneled. If unset, no host key checking will be done and the connection
+     * will be attempted regardless of the identity of the remote host.
+     */
+    char* ssh_tunnel_host_key;
+
+    /**
+     * The username to use when connecting to the SSH host to tunnel traffic.
+     * This is required if SSH tunneling is enabled.
+     */
+    char* ssh_tunnel_username;
+
+    /**
+     * The password to use when connecting to the SSH host to tunnel traffic,
+     * if password authentication is used.
+     */
+    char* ssh_tunnel_password;
+
+    /**
+     * The private key to use to authenticate to the SSH server to tunnel traffic,
+     * if key-based authentication is used.
+     */
+    char* ssh_tunnel_private_key;
+
+    /**
+     * The passphrase of the private key to use to decrypt the private key when
+     * using key-based authentication, if the key is encrypted.
+     */
+    char* ssh_tunnel_passphrase;
+
+    /**
+     * The interval at which keepalive messages will be sent to the SSH server
+     * over which the connection is being tunneled. The default is 0, meaning
+     * that keepalive messages will be disabled. The minimum value is 2 to avoid
+     * busy loop scenarios, and a value of 1 is automatically increased to 2 by
+     * the underlying libssh2 implementation.
+     */
+    int ssh_tunnel_alive_interval;
+
 #endif
 
     /**

src/protocols/vnc/vnc.c

@@ -38,6 +38,7 @@
 #ifdef ENABLE_COMMON_SSH
 #include "common-ssh/sftp.h"
 #include "common-ssh/ssh.h"
+#include "common-ssh/tunnel.h"
 #include "sftp.h"
 #endif
 
@@ -330,6 +331,98 @@ void* guac_vnc_client_thread(void* data) {
     rfbClientLog = guac_vnc_client_log_info;
     rfbClientErr = guac_vnc_client_log_error;
 
+#ifdef ENABLE_COMMON_SSH
+    /* If SSH tunneling is enabled, we set up the tunnel and redirect the connection. */
+    if (settings->ssh_tunnel) {
+
+        /* Allocate memory for the SSH tunnel data. */
+        vnc_client->ssh_tunnel = malloc(sizeof(guac_ssh_tunnel));
+
+        guac_client_log(client, GUAC_LOG_DEBUG,
+                "SSH tunneling is enabled, connecting via SSH.");
+
+        /* Associate the guac_client object with the tunnel. */
+        vnc_client->ssh_tunnel->client = client;
+
+        /* Abort if tunnel username is missing */
+        if (settings->ssh_tunnel_username == NULL) {
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "An SSH tunnel-specific username is required if "
+                    "SSH tunneling is enabled.");
+            return NULL;
+        }
+
+        vnc_client->ssh_tunnel->user =
+            guac_common_ssh_create_user(settings->ssh_tunnel_username);
+
+        /* Import SSH tunnel private key, if given */
+        if (settings->ssh_tunnel_private_key != NULL) {
+
+            guac_client_log(client, GUAC_LOG_DEBUG,
+                    "Authenticating SSH tunnel with private key.");
+
+            /* Abort if SSH tunnel private key cannot be read */
+            if (guac_common_ssh_user_import_key(vnc_client->ssh_tunnel->user,
+                        settings->ssh_tunnel_private_key,
+                        settings->ssh_tunnel_passphrase)) {
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                        "SSH tunnel private key unreadable.");
+                return NULL;
+            }
+
+        }
+
+        /* Otherwise, use specified SSH tunnel password */
+        else {
+
+            guac_client_log(client, GUAC_LOG_DEBUG,
+                    "Authenticating SSH tunnel with password.");
+
+            guac_common_ssh_user_set_password(vnc_client->ssh_tunnel->user,
+                    settings->ssh_tunnel_password);
+
+        }
+
+        /* Attempt SSH tunnel connection */
+        vnc_client->ssh_tunnel->session =
+            guac_common_ssh_create_session(client, settings->ssh_tunnel_host,
+                    settings->ssh_tunnel_port, vnc_client->ssh_tunnel->user,
+                    settings->ssh_tunnel_alive_interval,
+                    settings->ssh_tunnel_host_key, NULL);
+
+        /* Fail if SSH tunnel connection does not succeed */
+        if (vnc_client->ssh_tunnel->session == NULL) {
+            /* Already aborted within guac_common_ssh_create_session() */
+            return NULL;
+        }
+
+        guac_client_log(client, GUAC_LOG_DEBUG,
+                "SSH session created for tunneling, initializing the tunnel.");
+
+        /* Initialize the tunnel or fail. */
+        if (guac_common_ssh_tunnel_init(vnc_client->ssh_tunnel,
+                settings->hostname, settings->port)) {
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Unable to initialize SSH tunnel, aborting connection.");
+            return NULL;
+        }
+
+        /* If tunnel socket is not returned, bail out. */
+        if (vnc_client->ssh_tunnel->socket_path == NULL) {
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Unable to obtain socket for SSH tunnel, aborting.");
+            return NULL;
+        }
+
+        /* Overwrite the hostname with the path to the socket and zero out port. */
+        settings->hostname = guac_strdup(vnc_client->ssh_tunnel->socket_path);
+        settings->port = 0;
+
+        guac_client_log(client, GUAC_LOG_DEBUG,
+                "SSH tunnel connection succeeded.");
+    }
+#endif
+
     /* Attempt connection */
     rfbClient* rfb_client = guac_vnc_get_client(client);
     int retries_remaining = settings->retries;
@@ -363,7 +456,6 @@ void* guac_vnc_client_thread(void* data) {
 #endif
 
 #ifdef ENABLE_COMMON_SSH
-    guac_common_ssh_init(client);
 
     /* Connect via SSH if SFTP is enabled */
     if (settings->enable_sftp) {

src/protocols/vnc/vnc.h

@@ -39,6 +39,7 @@
 #ifdef ENABLE_COMMON_SSH
 #include "common-ssh/sftp.h"
 #include "common-ssh/ssh.h"
+#include "common-ssh/tunnel.h"
 #include "common-ssh/user.h"
 #endif
 
@@ -117,6 +118,11 @@ typedef struct guac_vnc_client {
      * An SFTP-based filesystem.
      */
     guac_common_ssh_sftp_filesystem* sftp_filesystem;
+
+    /**
+     * The data structure containing SSH tunnel-related information.
+     */
+    guac_ssh_tunnel* ssh_tunnel;
 #endif
 
     /**