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/*
* The remctl server as a restricted shell.
*
* This is a varient of remctld that, rather than listening to the network for
* the remctl protocol, runs as a restricted shell under ssh. It uses the
* same configuration and the same command semantics as the normal remctl
* server, but uses ssh as the transport mechanism and must be run under sshd.
*
* This file handles parsing of the user's command and the main control flow.
*
* Written by Russ Allbery
* Copyright 2016, 2018, 2020 Russ Allbery <eagle@eyrie.org>
* Copyright 2016 Dropbox, Inc.
*
* SPDX-License-Identifier: MIT
*/
#include <config.h>
#include <portable/event.h>
#include <portable/system.h>
#include <signal.h>
#include <syslog.h>
#include <server/internal.h>
#include <util/messages.h>
#include <util/xmalloc.h>
/* Usage message. */
static const char usage_message[] = "\
Usage: remctl-shell [-dhqSv] [-f <file>] -c <command>\n\
remctl-shell [-dqS] [-f <file>] <user>\n\
\n\
Options:\n\
-c <command> Specifies the command to run\n\
-d Log verbose debugging information\n\
-f <file> Config file (default: " CONFIG_FILE ")\n\
-h Display this help\n\
-q Suppress informational logging (such as the command run)\n\
-S Log to standard output/error rather than syslog\n\
-v Display the version of remctld\n\
\n\
This is meant to be used as the shell or forced command for a dedicated\n\
account, and handles incoming commands via ssh. It must be run under ssh\n\
or with the same environment variables ssh would set.\n\
\n\
Supported ACL methods: file, princ, deny";
/*
* Display the usage message for remctl-shell.
*/
__attribute__((__noreturn__)) static void
usage(int status)
{
FILE *output;
output = (status == 0) ? stdout : stderr;
if (status != 0)
fprintf(output, "\n");
fprintf(output, usage_message);
#ifdef HAVE_GPUT
fprintf(output, ", gput");
#endif
#if defined(HAVE_KRB5) && defined(HAVE_GETGRNAM_R)
fprintf(output, ", localgroup");
#endif
#ifdef HAVE_PCRE
fprintf(output, ", pcre");
#endif
#ifdef HAVE_REGCOMP
fprintf(output, ", regex");
#endif
fprintf(output, "\n");
exit(status);
}
/*
* Main routine. Parses the configuration file and the user's command and
* then dispatches running the command.
*/
int
main(int argc, char *argv[])
{
int option, status;
bool debug = false;
bool log_stdout = false;
bool quiet = false;
struct sigaction sa;
const char *command_string = NULL;
const char *user = NULL;
const char *config_path = CONFIG_FILE;
struct iovec **command;
struct client *client;
struct config *config;
/* Ignore SIGPIPE errors from our children. */
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_IGN;
if (sigaction(SIGPIPE, &sa, NULL) < 0)
sysdie("cannot set SIGPIPE handler");
/* Establish identity for logging. */
message_program_name = "remctl-shell";
/* Initialize the logging and fatal callbacks for libevent. */
event_set_log_callback(server_event_log_callback);
event_set_fatal_callback(server_event_fatal_callback);
/*
* Parse options. Since we're being run as a shell, there isn't all that
* much here.
*/
while ((option = getopt(argc, argv, "c:df:hqS")) != EOF) {
switch (option) {
case 'c':
command_string = optarg;
break;
case 'd':
debug = true;
break;
case 'f':
config_path = optarg;
break;
case 'h':
usage(0);
case 'q':
quiet = true;
break;
case 'S':
log_stdout = true;
break;
case 'v':
printf("remctl-shell %s\n", PACKAGE_VERSION);
exit(0);
default:
warn("unknown option -%c", optopt);
usage(1);
}
}
argc -= optind;
argv += optind;
/*
* If no command string was specified, the user must be specified as a
* command-line argument and we'll get the command string from the
* SSH_ORIGINAL_COMMAND environment variable. If a command string was
* specified, there must be no argument.
*/
if (command_string == NULL) {
if (argc != 1)
usage(1);
user = argv[0];
command_string = getenv("SSH_ORIGINAL_COMMAND");
if (command_string == NULL)
die("SSH_ORIGINAL_COMMAND not set in the environment");
} else {
if (argc > 0)
usage(1);
}
/* Set up logging. */
if (log_stdout) {
if (debug)
message_handlers_debug(1, message_log_stdout);
} else {
openlog("remctl-shell", LOG_PID | LOG_NDELAY, LOG_DAEMON);
message_handlers_notice(1, message_log_syslog_info);
message_handlers_warn(1, message_log_syslog_warning);
message_handlers_die(1, message_log_syslog_err);
if (debug)
message_handlers_debug(1, message_log_syslog_debug);
}
if (quiet)
message_handlers_notice(0);
/* Read the configuration file. */
config = server_config_load(config_path);
if (config == NULL)
die("cannot read configuration file %s", config_path);
/* Create the client struct based on the ssh environment. */
client = server_ssh_new_client(user);
/* Parse and execute the command. */
command = server_ssh_parse_command(command_string);
if (command == NULL)
die("cannot parse command: %s", command_string);
status = server_run_command(client, config, command);
server_free_command(command);
/* Clean up and exit. */
server_ssh_free_client(client);
server_config_free(config);
libevent_global_shutdown();
message_handlers_reset();
return status;
}
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