guacamole-spice-protocol/src/protocols/ssh/ssh.c

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/*
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* 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
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* 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.
*/
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#include "config.h"
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#include "common/recording.h"
#include "common-ssh/sftp.h"
#include "common-ssh/ssh.h"
#include "settings.h"
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#include "sftp.h"
#include "ssh.h"
#include "terminal/terminal.h"
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#ifdef ENABLE_SSH_AGENT
#include "ssh_agent.h"
#endif
#include <libssh2.h>
#include <libssh2_sftp.h>
#include <guacamole/client.h>
#include <openssl/err.h>
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#include <openssl/ssl.h>
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#ifdef LIBSSH2_USES_GCRYPT
#include <gcrypt.h>
#endif
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#include <errno.h>
#include <netdb.h>
#include <netinet/in.h>
#include <poll.h>
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#include <pthread.h>
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#include <stdbool.h>
#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
#include <sys/socket.h>
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#include <sys/time.h>
/**
* Produces a new user object containing a username and password or private
* key, prompting the user as necessary to obtain that information.
*
* @param client
* The Guacamole client containing any existing user data, as well as the
* terminal to use when prompting the user.
*
* @return
* A new user object containing the user's username and other credentials,
* or NULL if fails to import key.
*/
static guac_common_ssh_user* guac_ssh_get_user(guac_client* client) {
guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
guac_ssh_settings* settings = ssh_client->settings;
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guac_common_ssh_user* user;
/* Get username */
if (settings->username == NULL)
settings->username = guac_terminal_prompt(ssh_client->term,
"Login as: ", true);
/* Create user object from username */
user = guac_common_ssh_create_user(settings->username);
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/* If key specified, import */
if (settings->key_base64 != NULL) {
guac_client_log(client, GUAC_LOG_DEBUG,
"Attempting private key import (WITHOUT passphrase)");
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/* Attempt to read key without passphrase */
if (guac_common_ssh_user_import_key(user,
settings->key_base64, NULL)) {
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/* Log failure of initial attempt */
guac_client_log(client, GUAC_LOG_DEBUG,
"Initial import failed: %s",
guac_common_ssh_key_error());
guac_client_log(client, GUAC_LOG_DEBUG,
"Re-attempting private key import (WITH passphrase)");
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/* Prompt for passphrase if missing */
if (settings->key_passphrase == NULL)
settings->key_passphrase =
guac_terminal_prompt(ssh_client->term,
"Key passphrase: ", false);
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/* Reattempt import with passphrase */
if (guac_common_ssh_user_import_key(user,
settings->key_base64,
settings->key_passphrase)) {
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/* If still failing, give up */
guac_client_abort(client,
GUAC_PROTOCOL_STATUS_CLIENT_UNAUTHORIZED,
"Auth key import failed: %s",
guac_common_ssh_key_error());
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guac_common_ssh_destroy_user(user);
return NULL;
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}
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} /* end decrypt key with passphrase */
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/* Success */
guac_client_log(client, GUAC_LOG_INFO,
"Auth key successfully imported.");
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} /* end if key given */
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/* Otherwise, use password */
else {
/* Get password if not provided */
if (settings->password == NULL)
settings->password = guac_terminal_prompt(ssh_client->term,
"Password: ", false);
/* Set provided password */
guac_common_ssh_user_set_password(user, settings->password);
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}
/* Clear screen of any prompts */
guac_terminal_printf(ssh_client->term, "\x1B[H\x1B[J");
return user;
}
void* ssh_input_thread(void* data) {
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guac_client* client = (guac_client*) data;
guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
char buffer[8192];
int bytes_read;
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/* Write all data read */
while ((bytes_read = guac_terminal_read_stdin(ssh_client->term, buffer, sizeof(buffer))) > 0) {
pthread_mutex_lock(&(ssh_client->term_channel_lock));
libssh2_channel_write(ssh_client->term_channel, buffer, bytes_read);
pthread_mutex_unlock(&(ssh_client->term_channel_lock));
GUACAMOLE-384: fixing segfault during ssh disconnect Root Cause: See the core dump and Valgrind report posted on Jira. guacd was reading a ssh terminal which had been freed. When a ssh connection is terminated, guac_ssh_client_free_handler() will be called from guacd_exec_proc() -> guac_client_free() with pointer client->free_handler. In guac_ssh_client_free_handler(), when ssh_client->term is freed, ssh_client->client_thread may still be using the ssh_client->term. It causes the crash reported in this bug. The stack trace exposing the problem can be found by running guacd under Valgrind with a ssh test script. The test script repeats doing ssh login and logout for 5000 times. Solution: In guac_ssh_client_free_handler(), before calling guac_terminal_free(ssh_client->term), close the stdin pipe of the terminal to stop reading the pipe with guac_terminal_read_stdin() in ssh_input_thread(). So that ssh_input_thread() can be terminated in this case. Call pthread_join() to wait for ssh_client_thread() terminating before freeing the terminal. Add a new function guac_terminal_stop() to close the pipe and set the fds to invalid (-1). Call it in guac_ssh_client_free_handler() and guac_terminal_free(). Checking the client running state in ssh_input_thread() and ssh_client_thread() to make sure they can be terminated when the client is stopped in guacd_exec_proc() by another thread. Test: - Confirmed ssh connection works normally. - Observed the child process of guacd exits when ssh connection is terminated. - Reran the ssh test script. Observed no crash.
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/* Make sure ssh_input_thread can be terminated anyway */
if (client->state == GUAC_CLIENT_STOPPING)
break;
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}
GUACAMOLE-384: fixing segfault during ssh disconnect Root Cause: See the core dump and Valgrind report posted on Jira. guacd was reading a ssh terminal which had been freed. When a ssh connection is terminated, guac_ssh_client_free_handler() will be called from guacd_exec_proc() -> guac_client_free() with pointer client->free_handler. In guac_ssh_client_free_handler(), when ssh_client->term is freed, ssh_client->client_thread may still be using the ssh_client->term. It causes the crash reported in this bug. The stack trace exposing the problem can be found by running guacd under Valgrind with a ssh test script. The test script repeats doing ssh login and logout for 5000 times. Solution: In guac_ssh_client_free_handler(), before calling guac_terminal_free(ssh_client->term), close the stdin pipe of the terminal to stop reading the pipe with guac_terminal_read_stdin() in ssh_input_thread(). So that ssh_input_thread() can be terminated in this case. Call pthread_join() to wait for ssh_client_thread() terminating before freeing the terminal. Add a new function guac_terminal_stop() to close the pipe and set the fds to invalid (-1). Call it in guac_ssh_client_free_handler() and guac_terminal_free(). Checking the client running state in ssh_input_thread() and ssh_client_thread() to make sure they can be terminated when the client is stopped in guacd_exec_proc() by another thread. Test: - Confirmed ssh connection works normally. - Observed the child process of guacd exits when ssh connection is terminated. - Reran the ssh test script. Observed no crash.
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/* Stop the client so that ssh_client_thread can be terminated */
guac_client_stop(client);
return NULL;
}
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void* ssh_client_thread(void* data) {
guac_client* client = (guac_client*) data;
guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
guac_ssh_settings* settings = ssh_client->settings;
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char buffer[8192];
pthread_t input_thread;
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/* Init SSH base libraries */
if (guac_common_ssh_init(client)) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"SSH library initialization failed");
return NULL;
}
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/* Set up screen recording, if requested */
if (settings->recording_path != NULL) {
ssh_client->recording = guac_common_recording_create(client,
settings->recording_path,
settings->recording_name,
settings->create_recording_path);
}
/* Create terminal */
ssh_client->term = guac_terminal_create(client,
settings->font_name, settings->font_size,
settings->resolution, settings->width, settings->height,
settings->color_scheme);
/* Fail if terminal init failed */
if (ssh_client->term == NULL) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
"Terminal initialization failed");
return NULL;
}
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/* Set up typescript, if requested */
if (settings->typescript_path != NULL) {
guac_terminal_create_typescript(ssh_client->term,
settings->typescript_path,
settings->typescript_name,
settings->create_typescript_path);
}
/* Get user and credentials */
ssh_client->user = guac_ssh_get_user(client);
if (ssh_client->user == NULL) {
/* Already aborted within guac_ssh_get_user() */
return NULL;
}
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/* Open SSH session */
ssh_client->session = guac_common_ssh_create_session(client,
settings->hostname, settings->port, ssh_client->user, settings->server_alive_interval);
if (ssh_client->session == NULL) {
/* Already aborted within guac_common_ssh_create_session() */
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return NULL;
}
pthread_mutex_init(&ssh_client->term_channel_lock, NULL);
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/* Open channel for terminal */
ssh_client->term_channel =
libssh2_channel_open_session(ssh_client->session->session);
if (ssh_client->term_channel == NULL) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
"Unable to open terminal channel.");
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return NULL;
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}
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#ifdef ENABLE_SSH_AGENT
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/* Start SSH agent forwarding, if enabled */
if (ssh_client->enable_agent) {
libssh2_session_callback_set(ssh_client->session,
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LIBSSH2_CALLBACK_AUTH_AGENT, (void*) ssh_auth_agent_callback);
/* Request agent forwarding */
if (libssh2_channel_request_auth_agent(ssh_client->term_channel))
guac_client_log(client, GUAC_LOG_ERROR, "Agent forwarding request failed");
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else
guac_client_log(client, GUAC_LOG_INFO, "Agent forwarding enabled.");
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}
ssh_client->auth_agent = NULL;
#endif
/* Start SFTP session as well, if enabled */
if (settings->enable_sftp) {
/* Create SSH session specific for SFTP */
guac_client_log(client, GUAC_LOG_DEBUG, "Reconnecting for SFTP...");
ssh_client->sftp_session =
guac_common_ssh_create_session(client, settings->hostname,
settings->port, ssh_client->user, settings->server_alive_interval);
if (ssh_client->sftp_session == NULL) {
/* Already aborted within guac_common_ssh_create_session() */
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return NULL;
}
/* Request SFTP */
ssh_client->sftp_filesystem = guac_common_ssh_create_sftp_filesystem(
ssh_client->sftp_session, settings->sftp_root_directory,
NULL);
/* Expose filesystem to connection owner */
guac_client_for_owner(client,
guac_common_ssh_expose_sftp_filesystem,
ssh_client->sftp_filesystem);
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/* Init handlers for Guacamole-specific console codes */
ssh_client->term->upload_path_handler = guac_sftp_set_upload_path;
ssh_client->term->file_download_handler = guac_sftp_download_file;
guac_client_log(client, GUAC_LOG_DEBUG, "SFTP session initialized");
}
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/* Request PTY */
if (libssh2_channel_request_pty_ex(ssh_client->term_channel, "linux", sizeof("linux")-1, NULL, 0,
ssh_client->term->term_width, ssh_client->term->term_height, 0, 0)) {
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guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR, "Unable to allocate PTY.");
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return NULL;
}
/* If a command is specified, run that instead of a shell */
if (settings->command != NULL) {
if (libssh2_channel_exec(ssh_client->term_channel, settings->command)) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
"Unable to execute command.");
return NULL;
}
}
/* Otherwise, request a shell */
else if (libssh2_channel_shell(ssh_client->term_channel)) {
guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
"Unable to associate shell with PTY.");
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return NULL;
}
/* Logged in */
guac_client_log(client, GUAC_LOG_INFO, "SSH connection successful.");
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/* Start input thread */
if (pthread_create(&(input_thread), NULL, ssh_input_thread, (void*) client)) {
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guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR, "Unable to start input thread");
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return NULL;
}
/* Set non-blocking */
libssh2_session_set_blocking(ssh_client->session->session, 0);
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/* While data available, write to terminal */
int bytes_read = 0;
for (;;) {
/* Track total amount of data read */
int total_read = 0;
/* Timeout for polling socket activity */
int timeout;
pthread_mutex_lock(&(ssh_client->term_channel_lock));
/* Stop reading at EOF */
if (libssh2_channel_eof(ssh_client->term_channel)) {
pthread_mutex_unlock(&(ssh_client->term_channel_lock));
break;
}
GUACAMOLE-384: fixing segfault during ssh disconnect Root Cause: See the core dump and Valgrind report posted on Jira. guacd was reading a ssh terminal which had been freed. When a ssh connection is terminated, guac_ssh_client_free_handler() will be called from guacd_exec_proc() -> guac_client_free() with pointer client->free_handler. In guac_ssh_client_free_handler(), when ssh_client->term is freed, ssh_client->client_thread may still be using the ssh_client->term. It causes the crash reported in this bug. The stack trace exposing the problem can be found by running guacd under Valgrind with a ssh test script. The test script repeats doing ssh login and logout for 5000 times. Solution: In guac_ssh_client_free_handler(), before calling guac_terminal_free(ssh_client->term), close the stdin pipe of the terminal to stop reading the pipe with guac_terminal_read_stdin() in ssh_input_thread(). So that ssh_input_thread() can be terminated in this case. Call pthread_join() to wait for ssh_client_thread() terminating before freeing the terminal. Add a new function guac_terminal_stop() to close the pipe and set the fds to invalid (-1). Call it in guac_ssh_client_free_handler() and guac_terminal_free(). Checking the client running state in ssh_input_thread() and ssh_client_thread() to make sure they can be terminated when the client is stopped in guacd_exec_proc() by another thread. Test: - Confirmed ssh connection works normally. - Observed the child process of guacd exits when ssh connection is terminated. - Reran the ssh test script. Observed no crash.
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/* Client is stopping, break the loop */
if (client->state == GUAC_CLIENT_STOPPING) {
pthread_mutex_unlock(&(ssh_client->term_channel_lock));
break;
}
/* Send keepalive at configured interval */
if (settings->server_alive_interval > 0) {
timeout = 0;
if (libssh2_keepalive_send(ssh_client->session->session, &timeout) > 0)
break;
timeout *= 1000;
}
/* If keepalive is not configured, sleep for the default of 1 second */
else
timeout = GUAC_SSH_DEFAULT_POLL_TIMEOUT;
/* Read terminal data */
bytes_read = libssh2_channel_read(ssh_client->term_channel,
buffer, sizeof(buffer));
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pthread_mutex_unlock(&(ssh_client->term_channel_lock));
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/* Attempt to write data received. Exit on failure. */
if (bytes_read > 0) {
int written = guac_terminal_write(ssh_client->term, buffer, bytes_read);
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if (written < 0)
break;
total_read += bytes_read;
}
else if (bytes_read < 0 && bytes_read != LIBSSH2_ERROR_EAGAIN)
break;
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#ifdef ENABLE_SSH_AGENT
/* If agent open, handle any agent packets */
if (ssh_client->auth_agent != NULL) {
bytes_read = ssh_auth_agent_read(ssh_client->auth_agent);
if (bytes_read > 0)
total_read += bytes_read;
else if (bytes_read < 0 && bytes_read != LIBSSH2_ERROR_EAGAIN)
ssh_client->auth_agent = NULL;
}
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#endif
/* Wait for more data if reads turn up empty */
if (total_read == 0) {
/* Wait on the SSH session file descriptor only */
struct pollfd fds[] = {{
.fd = ssh_client->session->fd,
.events = POLLIN,
.revents = 0,
}};
/* Wait up to computed timeout */
if (poll(fds, 1, timeout) < 0)
break;
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}
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}
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/* Kill client and Wait for input thread to die */
guac_client_stop(client);
pthread_join(input_thread, NULL);
pthread_mutex_destroy(&ssh_client->term_channel_lock);
guac_client_log(client, GUAC_LOG_INFO, "SSH connection ended.");
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return NULL;
}