[WIP] Start of common settings for SSH tunneling.

This commit is contained in:
Virtually Nick 2023-02-18 08:45:27 -05:00
parent 47b9360d46
commit 3693601240
7 changed files with 622 additions and 62 deletions

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@ -25,6 +25,7 @@
AUTOMAKE_OPTIONS = foreign
ACLOCAL_AMFLAGS = -I m4
AM_CPPFLAGS = -DGUACD_STATE_DIR='"$(localstatedir)/run/guacd"'
noinst_LTLIBRARIES = libguac_common_ssh.la
SUBDIRS = . tests
@ -34,6 +35,7 @@ libguac_common_ssh_la_SOURCES = \
sftp.c \
ssh.c \
key.c \
tunnel.c \
user.c
noinst_HEADERS = \
@ -41,6 +43,7 @@ noinst_HEADERS = \
common-ssh/key.h \
common-ssh/sftp.h \
common-ssh/ssh.h \
common-ssh/tunnel.h \
common-ssh/user.h
libguac_common_ssh_la_CFLAGS = \

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@ -25,6 +25,8 @@
#include <guacamole/client.h>
#include <libssh2.h>
#define GUAC_COMMON_SSH_KEY_DEFAULT_KNOWN_HOSTS "/etc/guacamole/ssh_known_hosts"
/**
* OpenSSH v1 private keys are PEM-wrapped base64-encoded blobs. The encoded data begins with:
* "openssh-key-v1\0"

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@ -0,0 +1,40 @@
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
#ifndef GUAC_COMMON_SSH_CONSTANTS_H
#define GUAC_COMMON_SSH_CONSTANTS_H
/**
* The default port to use for SSH and SFTP connections.
*/
#define GUAC_COMMON_SSH_DEFAULT_PORT "22"
/**
* The default interval at which to send keepalives, which is zero, where
* keepalives will not be sent.
*/
#define GUAC_COMMON_SSH_DEFAULT_ALIVE_INTERVAL 0
/**
* For SFTP connections, the default root directory at which to start
* the session.
*/
#define GUAC_COMMON_SSH_SFTP_DEFAULT_ROOT "/"
#endif

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@ -0,0 +1,117 @@
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
#ifndef GUAC_COMMON_SSH_TUNNEL_H
#define GUAC_COMMON_SSH_TUNNEL_H
#include "common-ssh/ssh.h"
#include <libssh2.h>
#include <pthread.h>
/**
* Default backlog size for the socket used for the SSH tunnel.
*/
#define GUAC_COMMON_SSH_TUNNEL_BACKLOG_SIZE 8
/**
* The default directory mode that will be used to create the directory that
* will store the sockets.
*/
#define GUAC_COMMON_SSH_TUNNEL_DIRECTORY_MODE 0700
/**
* The default mode of the file that will be used to access the UNIX domain
* socket.
*/
#define GUAC_COMMON_SSH_TUNNEL_SOCKET_MODE 0600
/**
* A data structure that contains the elements needed to be passed between
* the various Guacamole Client protocol implementations and the common SSH
* tunnel code.
*/
typedef struct guac_ssh_tunnel {
/**
* The Guacamole Client that is using this SSH tunnel.
*/
guac_client* client;
/**
* The user and credentials for authenticating the SSH tunnel.
*/
guac_common_ssh_user* user;
/**
* The SSH session to use to tunnel the data.
*/
guac_common_ssh_session* session;
/**
* The libssh2 channel that will carry the tunnel data over the SSH connection.
*/
LIBSSH2_CHANNEL *channel;
/**
* The path to the local socket that will be used by guacd to communicate
* with the SSH tunnel.
*/
char* socket_path;
} guac_ssh_tunnel;
/**
* Initialize the SSH tunnel to the given host and port combination through
* the provided SSH session, and open a socket at the specified path for the
* communication. This function will place the absolute path of the domain
* socket in the socket_path variable and return zero on success or non-zero
* on failure.
*
* @param ssh_tunnel
* The data structure containing relevant SSH tunnel information, including
* the guac_client that initialized the tunnel and the various libssh2
* session and channel objects.
*
* @param host
* The hostname or IP address to connect to over the tunnel.
*
* @param port
* The TCP port to connect to over the tunnel.
*
* @return
* Zero on success, non-zero on failure.
*/
int guac_common_ssh_tunnel_init(guac_ssh_tunnel* ssh_tunnel,
char* remote_host,
int remote_port);
/**
* Clean up the SSH tunnel, shutting down the channel and freeing the
* various data items created for the tunnel.
*
* @param ssh_tunnel
* The guac_common_ssh_session used to establish the tunnel.
*
* @return
* Zero on success, non-zero on failure.
*/
int guac_common_ssh_tunnel_cleanup(guac_ssh_tunnel* ssh_tunnel);
#endif

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@ -185,7 +185,7 @@ int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* clien
/* Otherwise, we look for a ssh_known_hosts file within GUACAMOLE_HOME and read that in. */
else {
const char *guac_known_hosts = "/etc/guacamole/ssh_known_hosts";
const char *guac_known_hosts = GUAC_COMMON_SSH_KEY_DEFAULT_KNOWN_HOSTS;
if (access(guac_known_hosts, F_OK) != -1)
known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, guac_known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);

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@ -41,6 +41,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#ifdef LIBSSH2_USES_GCRYPT
@ -409,8 +410,37 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
guac_ssh_credential_handler* credential_handler) {
int retval;
int fd;
struct stat sb;
/* Hostname is a UNIX socket */
if (stat(hostname, &sb) == 0 && (sb.st_mode & S_IFMT) == S_IFSOCK) {
fd = socket(AF_UNIX, SOCK_STREAM, 0);
if (fd < 0) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Error opening UNIX socket: %s", strerror(errno));
return NULL;
}
struct sockaddr_un socket_addr = {
.sun_family = AF_UNIX
};
strncpy(socket_addr.sun_path, hostname, sizeof(socket_addr.sun_path) - 1);
if (connect(fd, (const struct sockaddr *) &socket_addr, sizeof(struct sockaddr_un))) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Error connecting to UNIX socket for SSH tunnel: %s",
hostname);
return NULL;
}
guac_client_log(client, GUAC_LOG_DEBUG,
"Connected SSH to UNIX socket at \"%s\"", hostname);
}
/* Normal hostname or IP. */
else {
struct addrinfo* addresses;
struct addrinfo* current_address;
@ -485,6 +515,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
"Unable to connect to any addresses.");
return NULL;
}
}
/* Allocate new session */
guac_common_ssh_session* common_session =

367
src/common-ssh/tunnel.c Normal file
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@ -0,0 +1,367 @@
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
#include "common-ssh/ssh.h"
#include "common-ssh/tunnel.h"
#include <guacamole/string.h>
#include <errno.h>
#include <libgen.h>
#include <libssh2.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <unistd.h>
/**
* A collection of the data required to establish the tunnel connection to the
* remote host over SSH and pass data between threads.
*/
typedef struct ssh_tunnel_data {
/**
* The SSH tunnel.
*/
guac_ssh_tunnel* ssh_tunnel;
/**
* The POSIX thread used to run the main tunnel worker.
*/
pthread_t tunnel_thread;
/**
* The POSIX thread used to run the tunnel input worker.
*/
pthread_t tunnel_input_thread;
/**
* A POSIX mutex lock used to manage concurrent access to the SSH2 channel.
*/
pthread_mutex_t tunnel_channel_lock;
/**
* The file descriptor of the socket that guacd will listen on to start
* the tunnel to the remote system.
*/
int listen_socket;
/**
* The file descriptor of the socket that will be used to read and write
* data to the remote tunnel.
*/
int tunnel_socket;
/**
* The UNIX address family data structure.
*/
struct sockaddr_un tunnel_addr;
/**
* The hostname or IP address of the remote host.
*/
char* remote_host;
/**
* The TCP port to connect to on the remote host.
*/
int remote_port;
} ssh_tunnel_data;
/**
* A function called by pthread_create that will be the worker function for
* incoming data on the SSH tunnel.
*
* @param data
* A pointer to the ssh_tunnel_parameters structure that contains the data
* required to pass data from the local system over the tunnel to the remote
* SSH server.
*/
static void* guac_common_ssh_tunnel_input_worker(void* data) {
ssh_tunnel_data* tunnel_data = (ssh_tunnel_data*) data;
char buffer[8192];
int bytes_read;
int retval = 0;
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Waiting for data on socket.");
/* Read data from the socket and write it to the channel. */
while (true) {
bytes_read = read(tunnel_data->tunnel_socket, buffer, sizeof(buffer));
if (bytes_read <= 0)
break;
pthread_mutex_lock(&(tunnel_data->tunnel_channel_lock));
libssh2_channel_write(tunnel_data->ssh_tunnel->channel, buffer, bytes_read);
pthread_mutex_unlock(&(tunnel_data->tunnel_channel_lock));
}
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Finished reading from socket, exiting.");
pthread_exit(&retval);
return NULL;
}
/**
* A function passed to phtread_create that will be the worker function for
* the SSH tunnel. The data passed should be a ssh_tunnel_parameters structure
* that contains all of the information this function will need to start
* the remote connection and process the data. Note that the socket passed
* via this data structure should already be in the LISTENING state by the
* time this function is called, and this function will wait for and accept
* a connection on the socket in order to start the process of connecting to
* the remote host over the tunnel and pass data.
*
* @param data
* A pointer to a ssh_tunnel_parameters structure that contains the data
* required to establish the connection over the SSH tunnel.
*/
static void* guac_common_ssh_tunnel_worker(void* data) {
ssh_tunnel_data* tunnel_data = (ssh_tunnel_data*) data;
int bytes_read, bytes_written, bytes_current;
int retval = 0;
char buffer[8192];
fd_set fds;
struct timeval tv;
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Starting tunnel worker - waiting for connection.");
// Wait for connections on the socket and accept one if it comes along.
socklen_t addr_len = sizeof(tunnel_data->tunnel_addr);
tunnel_data->tunnel_socket = accept(tunnel_data->listen_socket, (struct sockaddr*)(&(tunnel_data->tunnel_addr)), &addr_len);
if (tunnel_data->tunnel_socket < 0) {
pthread_exit(&retval);
return NULL;
}
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Connection received, starting libssh2 channel.");
// Start the libssh2 direct tcpip channel
tunnel_data->ssh_tunnel->channel = libssh2_channel_direct_tcpip(
tunnel_data->ssh_tunnel->session->session,
tunnel_data->remote_host,
tunnel_data->remote_port);
if (!tunnel_data->ssh_tunnel->channel) {
pthread_exit(&retval);
return NULL;
}
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG, "Channel started, starting output thread.");
libssh2_session_set_blocking(tunnel_data->ssh_tunnel->session->session, 0);
pthread_create(&(tunnel_data->tunnel_input_thread), NULL,
guac_common_ssh_tunnel_input_worker, (void *) tunnel_data);
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Processing tunnel data.");
// Process data
while (true) {
FD_ZERO(&fds);
FD_SET(tunnel_data->tunnel_socket, &fds);
tv.tv_sec = 0;
tv.tv_usec = 100000;
retval = select(tunnel_data->tunnel_socket, &fds, NULL, NULL, &tv);
if (retval < 0) {
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_ERROR,
"Error receiving data from socket.");
pthread_exit(&retval);
return NULL;
}
pthread_mutex_lock(&(tunnel_data->tunnel_channel_lock));
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_TRACE,
"Lock acquired, reading data from channel.");
bytes_read = libssh2_channel_read(tunnel_data->ssh_tunnel->channel,
buffer, sizeof(buffer));
pthread_mutex_unlock(&(tunnel_data->tunnel_channel_lock));
/* No data read from the channel, skip the rest of the loop. */
if (bytes_read == LIBSSH2_ERROR_EAGAIN)
continue;
if (bytes_read < 0) {
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_ERROR,
"Error reading from libssh2 channel, giving up.");
pthread_exit(&retval);
return NULL;
}
bytes_written = 0;
while (bytes_written < bytes_read) {
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_TRACE,
"Writing channel data to socket.");
bytes_current = send(tunnel_data->tunnel_socket,
buffer + bytes_written, bytes_read - bytes_written, 0);
if (bytes_current <= 0) {
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_ERROR,
"Error writing to socket, ending thread.");
pthread_exit(&retval);
return NULL;
}
bytes_written += bytes_current;
}
if (libssh2_channel_eof(tunnel_data->ssh_tunnel->channel)) {
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_ERROR,
"Received eof on libssh2 channel, giving up.");
pthread_exit(&retval);
return NULL;
}
}
guac_client_log(tunnel_data->ssh_tunnel->client, GUAC_LOG_DEBUG,
"Waiting for input thread to exit.");
// On error or when socket is closed, wait for input thread and exit
pthread_join(tunnel_data->tunnel_input_thread, NULL);
/* Close file descriptors and free data. */
close(tunnel_data->tunnel_socket);
close(tunnel_data->listen_socket);
free(tunnel_data->remote_host);
return NULL;
}
int guac_common_ssh_tunnel_init(guac_ssh_tunnel* ssh_tunnel, char* remote_host,
int remote_port) {
struct stat socket_stat;
ssh_tunnel_data* tunnel_data = calloc(1, sizeof(ssh_tunnel_data));
tunnel_data->ssh_tunnel = ssh_tunnel;
tunnel_data->remote_host = guac_strdup(remote_host);
tunnel_data->remote_port = remote_port;
// Create expected path to socket
ssh_tunnel->socket_path = malloc(4096);
snprintf(ssh_tunnel->socket_path, 4096, "%s/%s/tunnel",
GUACD_STATE_DIR, ssh_tunnel->client->connection_id);
guac_client_log(ssh_tunnel->client, GUAC_LOG_DEBUG,
"Socket: %s", ssh_tunnel->socket_path);
const char* socket_dir = dirname(guac_strdup(ssh_tunnel->socket_path));
// Check if socket already exists, and abort if it does
if (stat((const char *)ssh_tunnel->socket_path, &socket_stat) == 0) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_RESOURCE_CONFLICT,
"Socket already exists: %s", ssh_tunnel->socket_path);
return -1;
}
// Create directory and socket
if (mkdir(socket_dir, GUAC_COMMON_SSH_TUNNEL_DIRECTORY_MODE)) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Failed to make socket directory \"%s\": %s", socket_dir,
strerror(errno));
return -1;
}
// Set up socket and listen
int fd = socket(AF_UNIX, SOCK_STREAM, 0);
if (fd < 0) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Failed to create UNIX domain socket.");
return -1;
}
guac_client_log(ssh_tunnel->client, GUAC_LOG_DEBUG, "Socket created, binding.");
/* Bind to the UNIX domain socket. */
tunnel_data->tunnel_addr.sun_family = AF_UNIX;
strncpy(tunnel_data->tunnel_addr.sun_path, ssh_tunnel->socket_path,
sizeof(tunnel_data->tunnel_addr.sun_path) - 1);
if (bind(fd, (const struct sockaddr *) &tunnel_data->tunnel_addr, sizeof(struct sockaddr_un)) < 0) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Failed to bind to UNIX domain socket at \"%s\": %s",
ssh_tunnel->socket_path, strerror(errno));
return -1;
}
/* Listen on the UNIX domain socket for an incoming connection */
if (listen(fd, GUAC_COMMON_SSH_TUNNEL_BACKLOG_SIZE) < 0) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Failed to listen on UNIX domain socket at \"%s\": %s",
ssh_tunnel->socket_path, strerror(errno));
return -1;
}
tunnel_data->listen_socket = fd;
guac_client_log(ssh_tunnel->client, GUAC_LOG_DEBUG,
"Listening on socket, creating worker thread.");
/* Create a thread to wait for the incoming connection and do the work. */
int retval = pthread_create(&(tunnel_data->tunnel_thread), NULL, guac_common_ssh_tunnel_worker, (void *) tunnel_data);
if (retval) {
guac_client_abort(ssh_tunnel->client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Failed to start worker thread: %d", retval);
return -1;
}
guac_client_log(ssh_tunnel->client, GUAC_LOG_DEBUG,
"Worker created, return socket path to client.");
// Return success
return 0;
}
int guac_common_ssh_tunnel_cleanup(guac_ssh_tunnel* ssh_tunnel) {
/* Stop libssh2 channel and free it */
if (ssh_tunnel->channel) {
libssh2_channel_close(ssh_tunnel->channel);
libssh2_channel_free(ssh_tunnel->channel);
}
/* Clean up the SSH session */
if (ssh_tunnel->session)
guac_common_ssh_destroy_session(ssh_tunnel->session);
/* Remove socket and directory, and free string */
unlink(ssh_tunnel->socket_path);
rmdir(dirname(ssh_tunnel->socket_path));
free(ssh_tunnel->socket_path);
return 0;
}