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/******************************************************************

 * RebootDaemon.

 *

 * A daemon which waits on specified TCP port for special string

 * and reboots the computer.

 *

 * Command line: rebootdaemon [--port PORT] [--config CONFIG_FILE]

 * Defaults are port 19 and config /etc/rebootdaemon.conf.

 *

 * Config file looks like:

 * --------------------------

 * port=19

 * password="some password"

 * --------------------------

 *

 * Usage example (from any other host):

 * echo -n "some password" | nc host_to_rebot 19

 *

 * Copyleft 2005 Anatoli Klassen

 *

 ******************************************************************/

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <stdarg.h>

#include <ctype.h>

#include <errno.h>

#include <signal.h>

#include <unistd.h>

#include <netdb.h>

#include <syslog.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <sys/socket.h>

#include <sys/wait.h>

#include <sys/reboot.h>

#include <netinet/in.h>

#include <arpa/inet.h>

/* name version number */

#define APP_NAME          "RebootDaemon"

#define VERSION           "1.0"

#define REVISION          "$Rev: 1147 $"

#define DEFAULT_PORT      19

#define DEFAULT_CFG_FILE  "/etc/rebootdaemon.conf"

#define CMDSIZE           4096

#define BUFSIZE           4096

#define MAX_CONFIG_LINE   4096

#define PORT_MIN          1

#define PORT_MAX          65535

/* return values of functions */

#define RESULT_OK         0

#define RESULT_EXIT       1

#define RESULT_ERROR      2

#define RESULT_UNEXPECTED 3

/* return values for the whole program */

#define EXIT_OK           0

#define EXIT_USER_ERROR   1

#define EXIT_UNEXPECTED   2

/* command line and config file parameters */

#define PARAM_HELP_1      "-h"

#define PARAM_HELP_2      "--help"

#define PARAM_VERSION_1   "-v"

#define PARAM_VERSION_2   "--version"

#define PARAM_PORT_1      "-p"

#define PARAM_PORT_2      "--port"

#define PARAM_CONFIG_1    "-c"

#define PARAM_CONFIG_2    "--config"

#define CONFIG_PORT       "port"

#define CONFIG_PASSWORD   "password"

struct config {

	int  port;

	char password[MAX_CONFIG_LINE];

};

static int parse_cmd_line(int argc, char* argv[], long *port, char *config_name);

static int parse_config_file(char *config_name, long *port, char *password);

static int get_revision();

static int min(int a, int b)

{

	return (a < b) ? a : b;

}

static int establish(unsigned short portnum)

{

	int s;

	struct sockaddr_in sa;

	memset(&sa, 0, sizeof(struct sockaddr_in));

	sa.sin_family      = AF_INET;

	sa.sin_port        = htons(portnum);

	sa.sin_addr.s_addr = INADDR_ANY;

	if((s = socket(AF_INET, SOCK_STREAM, 0)) < 0)

		return -1;

	if(bind(s, (struct sockaddr *)&sa, sizeof(struct sockaddr_in)) < 0) {

		close(s);

		return -1;

	}

	listen(s, 1);

	return s;

}

static void listen_socket(struct config *cfg, int socket)

{

	int                t;

	char               cmd[CMDSIZE];

	char               buf[BUFSIZE];

	char*              msg;

	int                br;

	struct sockaddr_in sa;

	socklen_t          sa_len;

	for(;;) {

		sa_len = sizeof(sa);

		if((t = accept(socket, (struct sockaddr *)&sa, &sa_len)) < 0) {

			if(errno == EINTR) /* EINTR might happen on accept(), */

				continue;        /* try again */

			msg = strerror(errno);

			syslog(LOG_ERR, "cannot get connection, %s", msg);

			continue;

		}

		msg = inet_ntoa(sa.sin_addr);

		syslog(LOG_INFO, "connect from %s", msg);

		cmd[0] = '\0';

		while((br = recv(t, buf, BUFSIZE, 0)) > 0) {

			strncat(cmd, buf, min(br, sizeof(cmd) - strlen(cmd) - 1));

		}

		sleep(1);

		close(t);

		syslog(LOG_INFO, "got command");

		if(0 == strncmp(cmd, cfg->password, sizeof(cmd))) {

			syslog(LOG_EMERG, "REBOOT");

			sleep(5);

			if(reboot(RB_AUTOBOOT) < 0) {

				msg = strerror(errno);

				syslog(LOG_ERR, "cannot reboot, %s", msg);

			}

		}

	}

}

static void print_version()

{

	printf("%s %s.%d\n", APP_NAME, VERSION, get_revision());

}

static void pring_usage(int argc, char* argv[])

{

	print_version();

	printf("\nA daemon which waits on specified TCP port for special string and reboots the computer.\n\n");

	printf("Usage: %s [--port PORT] [--config CONFIG_FILE]\n", argv[0]);

	printf("   or: %s --version\n", argv[0]);

	printf("   or: %s --help\n\n", argv[0]);

	printf("Defaults are port 19 and config /etc/rebootdaemon.conf.\n\n");

	printf("Config file looks like:\n--------------------------\n");

	printf("port=19\npassword=\"some password\"\n--------------------------\n\n");

	printf("Then run from any other host:\necho -n \"some password\" | nc host_to_rebot 19\n");

}

static int print_cmd_error(int argc, char* argv[], char *msg, char *value)

{

	fprintf(stderr, "%s", msg);

	if(value) fprintf(stderr, " - %s\n", value);

	fprintf(stderr, "\n");

	pring_usage(argc, argv);

	return RESULT_ERROR;

}

static int print_config_error(char *config_name, int line, char *msg, char *value)

{

	fprintf(stderr, "Error in %s, line %d: %s", config_name, line, msg);

	if(value) fprintf(stderr, " - %s", value);

	fprintf(stderr, "\n");

	return RESULT_ERROR;

}

/* return: 0 - no error, continue; 1 - no error, but exit; 2 - user error, exit; 3 - unexpected error, exit */

static int read_config(struct config *cfg, int argc, char* argv[])

{

	int  res_cmd_line;

	int  res_config_file;

	long cmd_port;

	long file_port;

	char cmd_config[MAX_CONFIG_LINE];

	res_cmd_line = parse_cmd_line(argc, argv, &cmd_port, cmd_config);

	if(res_cmd_line != RESULT_OK) return res_cmd_line;

	res_config_file = parse_config_file(cmd_config[0] != '\0' ? cmd_config : DEFAULT_CFG_FILE,

		&file_port, cfg->password);

	if(res_config_file != RESULT_OK) return res_config_file;

	if(cfg->password[0] == '\0') {

		fprintf(stderr, "Password is not set\n");

		return RESULT_ERROR;

	}

	if(cmd_port > 0)

		cfg->port = (int)cmd_port;

	else if(file_port > 0)

		cfg->port = (int)file_port;

	else

		cfg->port = DEFAULT_PORT;

	return RESULT_OK;

}

static int parse_cmd_line(int argc, char* argv[], long *port, char *config_name)

{

	char *end;

	int  i;

	*port          = 0;

	config_name[0] = '\0';

	for(i = 1; i < argc; i++) {

		if(0 == strcmp(argv[i], PARAM_PORT_1) || 0 == strcmp(argv[i], PARAM_PORT_2)) {

			if(*port > 0)

				return print_cmd_error(argc, argv, "Port is already set", NULL);

			if(++i < argc) {

				*port = strtol(argv[i], &end, 10);

				if(*end != '\0' || *port < PORT_MIN || *port > PORT_MAX)

					return print_cmd_error(argc, argv, 

						"Port number must be integer between 1 and 65535", NULL);

			}

			else {

				return print_cmd_error(argc, argv, "Port number expected", NULL);

			}

		}

		else if(0 == strcmp(argv[i], PARAM_CONFIG_1) || 0 == strcmp(argv[i], PARAM_CONFIG_2)) {

			if(config_name[0] != '\0')

				return print_cmd_error(argc, argv, "Config file is already set", NULL);

			if(++i < argc) {

				strncpy(config_name, argv[i], MAX_CONFIG_LINE);

				if(config_name[MAX_CONFIG_LINE - 1] != '\0')

					return print_cmd_error(argc, argv, "Config file name is too long", NULL);

			}

			else {

				return print_cmd_error(argc, argv, "Config file expected", NULL);

			}

		}

		else if(0 == strcmp(argv[i], PARAM_VERSION_1) || 0 == strcmp(argv[i], PARAM_VERSION_2)) {

			print_version();

			return RESULT_EXIT;

		}

		else if(0 == strcmp(argv[i], PARAM_HELP_1) || 0 == strcmp(argv[i], PARAM_HELP_2)) {

			pring_usage(argc, argv);

			return RESULT_EXIT;

		}

		else {

			return print_cmd_error(argc, argv, "Unknown parameter", argv[i]);

		}

	}

	return RESULT_OK;

}

static int parse_config_file(char *config_name, long *port, char *password)

{

	FILE *config_file;

	char buf[MAX_CONFIG_LINE];

	char *line;

	char *subline;

	char *cur;

	int  count;

	config_file = fopen(config_name, "r");

	if(!config_file) {

		fprintf(stderr, "Can not open config file %s: %s\n", config_name, strerror(errno));

		return RESULT_ERROR;

	}

	count = 0;

	while(fgets(buf, sizeof(buf), config_file)) {

		count++;

		line = buf;

		/* skip end spaces */

		int len = strlen(line);

		if(len == MAX_CONFIG_LINE-1)

			return print_config_error(config_name, count, "Line is too long", NULL);

		while(len && isspace(line[len-1])) --len;

		if(!len) continue;

		line[len] = '\0';

		/* skip begin spaces */

		while(line[0] != '\0' && isspace(line[0])) line++;

		if('#' == line[0]) { /* skip comment lines */

			continue;

		}

		else if(strncmp(line, CONFIG_PORT, min(sizeof(CONFIG_PORT) - 1, len)) == 0) {

			subline = line + sizeof(CONFIG_PORT) - 1;

			if('=' != subline[0] && !isspace(subline[0]))

				return print_config_error(config_name, count, "Unknown config parameter", line);

			while(subline[0] != '\0' && isspace(subline[0])) subline++;

			if('=' != subline[0])

				return print_config_error(config_name, count, "Equal sign expected", NULL);

			subline++;

			*port = strtol(subline, &subline, 10);

			if(*port < PORT_MIN || *port > PORT_MAX)

				return print_config_error(config_name, count, 

					"Port number must be integer between 1 and 65535", NULL);

			while(subline[0] != '\0' && isspace(subline[0])) subline++;

			if('\0' != subline[0] && '#' != subline[0])

				return print_config_error(config_name, count, "End of line expected", NULL);

		}

		else if(strncmp(line, CONFIG_PASSWORD, min(sizeof(CONFIG_PASSWORD) - 1, len)) == 0) {

			subline = line + sizeof(CONFIG_PASSWORD) - 1;

			if('=' != subline[0] && !isspace(subline[0]))

				return print_config_error(config_name, count, "Unknown config parameter", line);

			while(subline[0] != '\0' && isspace(subline[0])) subline++;

			if('=' != subline[0])

				return print_config_error(config_name, count, "Equal sign expected", NULL);

			subline++;

			while(subline[0] != '\0' && isspace(subline[0])) subline++;

			if('"' != subline[0])

				return print_config_error(config_name, count, "Open quot expected", NULL);

			subline++;

			cur = password;

			while(subline[0] != '\0' && subline[0] != '"') {

				cur[0] = subline[0];

				cur++;

				subline++;

			}

			cur[0] = '\0';

			if('"' != subline[0])

				return print_config_error(config_name, count, "Close quot expected", NULL);

			subline++;

			while(subline[0] != '\0' && isspace(subline[0])) subline++;

			if('\0' != subline[0] && '#' != subline[0])

				return print_config_error(config_name, count, "End of line expected", NULL);

		}

		else {

			return print_config_error(config_name, count, "Unknown config parameter", line);

		}

	}

	if(fclose(config_file) != 0) {

		fprintf(stderr, "Can not close config file %s: %s\n", config_name, strerror(errno));

		return RESULT_UNEXPECTED;

	}

	return RESULT_OK;

}

static int get_revision()

{

	int  r;

	char *begin;

	begin = REVISION;

	while(begin[0] != '\0' && begin[0] != ':') begin++;

	if(begin[0] == '\0') return 0;

	begin++;

	r = strtol(begin, (char**)NULL, 10);

	return r;

}

static int create_child(int socket)

{

	pid_t child;

	child = fork();

	if(child == -1) {

		fprintf(stderr, "Cannot fork: %s\n", strerror(errno));

		return RESULT_UNEXPECTED; /* an unexpected error */

	}

	else if(child > 0) {

		if(close(socket) != 0) {

			fprintf(stderr, "Cannot close socket: %s\n", strerror(errno));

			return RESULT_UNEXPECTED; /* an unexpected error */

		}

		return RESULT_EXIT; /* we are the parent */

	}

	else {

		return RESULT_OK; /* we are the child */

	}

}

static int close_descr(int d)

{

	if(close(d) != 0) {

		syslog(LOG_ERR, "Cannot close descriptor %d: %s\n", d, strerror(errno));

		return RESULT_UNEXPECTED;

	}

	return RESULT_OK;

}

int main(int argc, char* argv[])

{

	int           socket;

	struct config cfg;

	/* get config */

	switch(read_config(&cfg, argc, argv)) {

		case RESULT_EXIT:       return EXIT_OK;           // no error but exit

		case RESULT_ERROR:      return EXIT_USER_ERROR;   // user error

		case RESULT_UNEXPECTED: return EXIT_UNEXPECTED;   // unexpected error

	}

	/* try to listen the port */

	if((socket = establish(cfg.port)) < 0) {

		fprintf(stderr, "Cannot listen to port %i\n", cfg.port);

		return EXIT_USER_ERROR;

	}

	/* fork and release the console */

	switch(create_child(socket)) {

		case RESULT_EXIT:       return EXIT_OK;           // no error but exit

		case RESULT_ERROR:      return EXIT_USER_ERROR;   // user error

		case RESULT_UNEXPECTED: return EXIT_UNEXPECTED;   // unexpected error

	}

	/* continue as first child */

	if(setsid() == -1) {

		fprintf(stderr, "Cannot create session: %s\n", strerror(errno));

		return EXIT_UNEXPECTED;

	}

	/* fork the second time */

	switch(create_child(socket)) {

		case RESULT_EXIT:       return EXIT_OK;           // no error but exit

		case RESULT_ERROR:      return EXIT_USER_ERROR;   // user error

		case RESULT_UNEXPECTED: return EXIT_UNEXPECTED;   // unexpected error

	}

	/* continue as final child, from now do not use console for error output */

	chdir("/");

	umask(0);

	if(close_descr(0) != RESULT_OK) return EXIT_UNEXPECTED;

	if(close_descr(1) != RESULT_OK) return EXIT_UNEXPECTED;

	if(close_descr(2) != RESULT_OK) return EXIT_UNEXPECTED;

	syslog(LOG_INFO, "listen on %d", cfg.port);

	listen_socket(&cfg, socket);

	return EXIT_OK; // unreachedable

}