guacamole-spice-protocol/src/protocols/ssh/client.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 "client.h"
#include "common-ssh/sftp.h"
#include "ssh.h"
#include "terminal/terminal.h"
#include "user.h"
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#include <langinfo.h>
#include <locale.h>
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#include <stdlib.h>
#include <string.h>
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#include <guacamole/client.h>
int guac_client_init(guac_client* client) {
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/* Set client args */
client->args = GUAC_SSH_CLIENT_ARGS;
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/* Allocate client instance data */
guac_ssh_client* ssh_client = calloc(1, sizeof(guac_ssh_client));
client->data = ssh_client;
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/* Set handlers */
client->join_handler = guac_ssh_user_join_handler;
client->free_handler = guac_ssh_client_free_handler;
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/* Set locale and warn if not UTF-8 */
setlocale(LC_CTYPE, "");
if (strcmp(nl_langinfo(CODESET), "UTF-8") != 0) {
guac_client_log(client, GUAC_LOG_INFO,
"Current locale does not use UTF-8. Some characters may "
"not render correctly.");
}
/* Success */
return 0;
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}
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int guac_ssh_client_free_handler(guac_client* client) {
guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
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/* Close SSH channel */
if (ssh_client->term_channel != NULL) {
libssh2_channel_send_eof(ssh_client->term_channel);
libssh2_channel_close(ssh_client->term_channel);
}
/* Free terminal (which may still be using term_channel) */
if (ssh_client->term != NULL) {
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 terminal to unblock any pending reads/writes */
guac_terminal_stop(ssh_client->term);
/* Wait ssh_client_thread to finish before freeing the terminal */
pthread_join(ssh_client->client_thread, NULL);
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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guac_terminal_free(ssh_client->term);
}
/* Free terminal channel now that the terminal is finished */
if (ssh_client->term_channel != NULL)
libssh2_channel_free(ssh_client->term_channel);
/* Clean up the SFTP filesystem object and session */
if (ssh_client->sftp_filesystem) {
guac_common_ssh_destroy_sftp_filesystem(ssh_client->sftp_filesystem);
guac_common_ssh_destroy_session(ssh_client->sftp_session);
}
/* Free interactive SSH session */
if (ssh_client->session != NULL)
guac_common_ssh_destroy_session(ssh_client->session);
/* Free SSH client credentials */
if (ssh_client->user != NULL)
guac_common_ssh_destroy_user(ssh_client->user);
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/* Free parsed settings */
if (ssh_client->settings != NULL)
guac_ssh_settings_free(ssh_client->settings);
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/* Free client structure */
free(ssh_client);
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guac_common_ssh_uninit();
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return 0;
}