sshoutcfg.c - net/sshout-daemon - Rivoreo Source Code Repositories

 /*
  * Copyright 2015-2018 Rivoreo
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
  * Free Software Foundation, either version 3 of the License, or (at your
  * option) any later version.
  *
  * This program is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  * more details.
  */

 #include "common.h"
 #include "syncrw.h"
 #include <unistd.h>
 #include <fcntl.h>
 #include <pwd.h>
 #include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <errno.h>
 #include <sys/stat.h>

 static void print_usage(const char *);

 static int fgetline(FILE *f, char *line, size_t len) {
 	size_t i = 0;
 	int c;
 	while((c = fgetc(f)) != '\n') {
 		if(c == EOF) {
 			if(!i) return -1;
 			break;
 		}
 		if(i >= len - 1) return -2;
 		line[i++] = c;
 	}
 	line[i] = 0;
 	return i;
 }

 static int read_user_info(FILE *f, char **name, char **public_key) {
 	int i = 0;
 	char line[4096];
 	while(1) {
 		i++;
 		int len = fgetline(f, line, sizeof line);
 		if(len == -2) {
 			int c;
 			fprintf(stderr, "Warning: line %u in file " USER_LIST_FILE " is too long, skipping\n", i);
 			while((c = fgetc(f)) != EOF && c != '\n');
 			continue;
 		}
 		if(len < 0) return -1;	// EOF
 		if(len == 0 || *line == '#') continue;
 		char *p = line;
 		while(*p && (*p == ' ' || *p == '	')) p++;
 		if(!*p) continue;
 		char *q1 = strchr(p, '"');
 		if(!q1) {
 			fprintf(stderr, "Warning: cannot find '\"' at line %u in file " USER_LIST_FILE "\n", i);
 			continue;
 		}
 		*q1 = 0;
 		if(q1 - p < 8 || strcmp(q1 - 8, "command=") || strchr(p, ' ')) {
 			fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", i);
 			continue;
 		}
 		q1++;
 		char *q2 = strchr(q1, '"');
 		if(!q2) {
 			fprintf(stderr, "Warning: unmatched '\"' in file " USER_LIST_FILE " line %u\n", i);
 			continue;
 		}
 		char *space = strchr(q2 + 1, ' ');
 		if(!space) {
 			fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", i);
 			continue;
 		}
 		size_t user_name_len = q2 - q1;
 		if(!user_name_len) {
 			fprintf(stderr, "Warning: empty user name in file " USER_LIST_FILE " line %u\n", i);
 			continue;
 		}
 		*name = malloc(user_name_len + 1);
 		if(!*name) {
 			fprintf(stderr, "Error: allocate %zu bytes failed when processing file " USER_LIST_FILE " line %u\n", user_name_len + 1, i);
 			return -1;
 		}
 		memcpy(*name, q1, user_name_len);
 		(*name)[user_name_len] = 0;
 		*public_key = strdup(space + 1);
 		if(!*public_key) {
 			fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", i);
 			return -1;
 		}
 		return 0;
 	}
 }

 static int remove_ssh_rc_file() {
 	struct stat st;
 	if(lstat(".ssh/rc", &st) < 0) {
 		if(errno == ENOENT) return 0;
 		perror(".ssh/rc");
 		return -1;
 	}
 	if(S_ISDIR(st.st_mode)) {
 		fputs("'.ssh/rc' exists, and it is a directory!\n", stderr);
 		return -1;
 	}
 	fputs("sshout shouldn't have a SSH RC file '.ssh/rc'; removing\n", stderr);
 	if(unlink(".ssh/rc") < 0) {
 		perror("unlink: .ssh/rc");
 		return -1;
 	}
 	return 0;
 }

 static int adduser_command(int argc, char **argv) {
 	char *key = NULL;
 	int force = 0;
 	while(1) {
 		int c = getopt(argc, argv, "a:fh");
 		if(c == -1) break;
 		switch(c) {
 			case 'a':
 				key = strdup(optarg);
 				if(!key) {
 					perror("strdup");
 					return 1;
 				}
 				break;
 			case 'f':
 				force = 1;
 				break;
 			case 'h':
 				print_usage(argv[0]);
 				return 0;
 			case '?':
 				return -1;
 		}
 	}
 	//fprintf(stderr, "optind = %d, argc = %d\n", optind, argc);
 	if(argc - optind != 1) {
 		print_usage(argv[0]);
 		return -1;
 	}
 	const char *user = argv[optind];
 	if(!key) {
 		key = malloc(4096);
 		if(!key) {
 			perror("malloc");
 			return 1;
 		}
 		fprintf(stderr, "Input public key for %s: ", user);
 		if(fgetline(stdin, key, 4096) == -2) {
 			free(key);
 			fputs("Public key too long\n", stderr);
 			return 1;
 		}
 	}

 	// TODO: verify the key format

 	struct stat st;
 	if(stat(".ssh", &st) == 0) {
 		if(!S_ISDIR(st.st_mode)) {
 			free(key);
 			fputs("'.ssh' is not a directory\n", stderr);
 			return 1;
 		}
 		uid_t myuid = getuid();
 		if(st.st_uid != myuid) {
 			free(key);
 			fprintf(stderr, "'.ssh' is not owned by sshout (%u != %u)\n", st.st_uid, myuid);
 			return 1;
 		}
 		if(st.st_mode & S_IWOTH) {
 			fputs("'.ssh' is global writable\n", stderr);
 			if(chmod(".ssh", st.st_mode & ~(S_IWOTH)) < 0) {
 				perror("chmod: .ssh");
 				free(key);
 				return 1;
 			}
 			fputs("fixed\n", stderr);
 		}
 		if(remove_ssh_rc_file() < 0) {
 			free(key);
 			fputs("Cannot continue\n", stderr);
 			return 1;
 		}
 	} else if(mkdir(".ssh", 0755) < 0) {
 		perror("mkdir: .ssh");
 		free(key);
 		return 1;
 	}

 	FILE *f = fopen(USER_LIST_FILE, "a+");
 	if(!f) {
 		perror(USER_LIST_FILE);
 		free(key);
 		return 1;
 	}

 	int existing_count = 0;
 	{
 		char *user_name, *public_key;
 		while(read_user_info(f, &user_name, &public_key) == 0) {
 			if(strcmp(key, public_key) == 0) {
 				free(key);
 				fprintf(stderr, "This public key is already used by user %s.\n"
 					"Are you pasted wrong key?\n", user_name);
 				free(user_name);
 				free(public_key);
 				return 1;
 			}
 			if(strcmp(user, user_name) == 0) existing_count++;
 			free(user_name);
 			free(public_key);
 		}
 	}
 	if(existing_count) {
 		fprintf(stderr, "%d key%s already exist for user %s\n", existing_count, existing_count > 1 ? "s" : "", user);
 		if(!force) {
 			char answer[16];
 			fprintf(stderr, "Are you sure you want to add this key for user %s? ", user);
 			do {
 				int len = fgetline(stdin, answer, sizeof answer);
 				// Ignore line too long error
 				if(len == -1 || strncasecmp(answer, "no", 2) == 0 || strncmp(answer, "不", 3) == 0 || strcmp(answer, "否") == 0) {
 					fputs("Operation canceled\n", stderr);
 					free(key);
 					return 1;
 				}
 			} while(strncasecmp(answer, "yes", 3) && strncmp(answer, "是", 3) && strncmp(answer, "好", 3) && strcmp(answer, "可以"));
 		}
 	}

 	if(fprintf(f, "command=\"%s\",no-agent-forwarding,no-port-forwarding %s\n", user, key) < 0) {
 		perror("fprintf");
 		free(key);
 		return 1;
 	}
 	free(key);
 	return -1;
 }

 static int listuser_command(int argc, char **argv) {
 	if(remove_ssh_rc_file() < 0) {
 		fputs("Warning: configuration error left unresolved\n", stderr);
 	}

 	FILE *f = fopen(USER_LIST_FILE, "r");
 	if(!f) {
 		perror(USER_LIST_FILE);
 		return 1;
 	}

 /*
 	char line[4096];
 	while(fgetline(f, line, sizeof line) > 0) {
 		fprintf(stderr, "line = \"%s\"\n", line);
 	}
 */
 	char *user_name, *public_key;
 	while(read_user_info(f, &user_name, &public_key) == 0) {
 		fprintf(stderr, "User \"%s\", Public key \"%s\"\n", user_name, public_key);
 		free(user_name);
 		free(public_key);
 	}
 	return 0;
 }

 static int getmotd_command(int argc, char **argv) {
 	char buffer[4096];
 	int fd = open(SSHOUT_MOTD_FILE, O_RDONLY);
 	if(fd == -1) {
 		perror(SSHOUT_MOTD_FILE);
 		return 1;
 	}
 	while(1) {
 		int s = sync_read(fd, buffer, sizeof buffer);
 		if(s < 0) {
 			perror("read");
 			return 1;
 		}
 		if(!s) return 0;
 		s = sync_write(STDOUT_FILENO, buffer, s);
 		if(s < 0) {
 			perror("write");
 			return 1;
 		}
 	}
 }

 static int setmotd_command(int argc, char **argv) {
 	const char *message = NULL;
 	int need_del = 0;
 	while(1) {
 		int c = getopt(argc, argv, "m:dh");
 		if(c == -1) break;
 		switch(c) {
 			case 'm':
 				message = optarg;
 				break;
 			case 'd':
 				need_del = 1;
 				break;
 			case 'h':
 				print_usage(argv[0]);
 				return 0;
 			case '?':
 				return -1;
 		}
 	}
 	if(need_del) {
 		if(message) {
 			fputs("Option '-d' cannot be used together with '-m'\n", stderr);
 			return -1;
 		}
 		if(unlink(SSHOUT_MOTD_FILE) < 0) {
 			perror(SSHOUT_MOTD_FILE);
 			return 1;
 		}
 		return 0;
 	}
 	int fd = creat(SSHOUT_MOTD_FILE, 0600);
 	if(fd == -1) {
 		perror(SSHOUT_MOTD_FILE);
 		return 1;
 	}
 	if(message) {
 		size_t len = strlen(message);
 		int s = sync_write(fd, message, len);
 		if(s < 0) {
 			perror("write");
 			return 1;
 		}
 		if(len && message[len - 1] != '\n') {
 			char new_line = '\n';
 			if(sync_write(fd, &new_line, 1) < 0) {
 				perror("write");
 				return 1;
 			}
 		}
 		return 0;
 	} else {
 		char buffer[4096];
 		if(isatty(STDIN_FILENO)) fputs("Type message below:\n", stderr);
 		while(1) {
 			int s = read(STDIN_FILENO, buffer, sizeof buffer);
 			if(s < 0) {
 				if(errno == EINTR) continue;
 				perror("read");
 				return 1;
 			}
 			if(!s) return 0;
 			s = sync_write(fd, buffer, s);
 			if(s < 0) {
 				perror("write");
 				return 1;
 			}
 		}
 	}
 }

 static struct subcommand {
 	const char *name;
 	const char *usage;
 	int (*func)(int, char **);
 } commands[] = {
 #define SUBCOMMAND(N,U) { #N, U, N##_command }
 	SUBCOMMAND(adduser, "[-a <public-key-in-base64>] [-f] <user-name>"),
 	SUBCOMMAND(listuser, ""),
 	SUBCOMMAND(getmotd, ""),
 	SUBCOMMAND(setmotd, "[-m <message> | -d]"),
 #undef SUBCOMMAND
 	{ NULL, NULL }
 };

 static void print_commands() {
 	struct subcommand *c = commands;
 	fputs("Following subcommands are available:\n", stderr);
 	while(c->name) {
 		fprintf(stderr, "	%s %s\n", c->name, c->usage);
 		c++;
 	}
 }

 static void print_usage(const char *name) {
 	struct subcommand *c = commands;
 	while(c->name) {
 		if(strcmp(c->name, name) == 0) {
 			fprintf(stderr, "Usage: %s %s\n", name, c->usage);
 			return;
 		}
 		c++;
 	}
 	fprintf(stderr, "Error: cannot find usage for command '%s'", name);
 }

 int main(int argc, char **argv) {
 	struct passwd *pw = getpwnam("sshout");
 	if(!pw) {
 		fputs("sshout user account not exist\n", stderr);
 		return 1;
 	}
 	if(pw->pw_uid == 0) {
 		fputs("sshout user account have UID 0\n", stderr);
 		return 1;
 	}

 	if(argc < 2) {
 		print_commands();
 		return -1;
 	}

 	uid_t myeuid = geteuid();
 	if(myeuid == 0) {
 		if(setreuid(pw->pw_uid, pw->pw_uid) < 0) {
 			perror("setreuid");
 			return 1;
 		}
 	} else if(myeuid != pw->pw_uid) {
 		fprintf(stderr, "Current effective UID %u doesn't equal to sshout user account\n", myeuid);
 		return 1;
 	}

 	const char *home = pw->pw_dir;
 	struct stat st;
 	if(stat(home, &st) < 0) {
 		perror(home);
 		return 1;
 	}
 	if(st.st_uid != pw->pw_uid) {
 		fprintf(stderr, "Home directory '%s' is not owned by sshout (expecting UID=%u, got %u)\n", home, pw->pw_uid, st.st_uid);
 		return 1;
 	}
 	setenv("HOME", home, 1);
 	if(chdir(home) < 0) {
 		perror(home);
 		return 1;
 	}

 	struct subcommand *c = commands;
 	while(c->name) {
 		if(strcmp(argv[1], c->name) == 0) return c->func(argc - 1, argv + 1);
 		c++;
 	}
 	fprintf(stderr, "Unknown command '%s'\n", argv[1]);
 	print_commands();
 	return -1;
 }
	/*
	* Copyright 2015-2018 Rivoreo
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License as published by the
	* Free Software Foundation, either version 3 of the License, or (at your
	* option) any later version.
	*
	* This program is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	* more details.
	*/

	#include "common.h"
	#include "syncrw.h"
	#include <unistd.h>
	#include <fcntl.h>
	#include <pwd.h>
	#include <string.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <errno.h>
	#include <sys/stat.h>

	static void print_usage(const char *);

	static int fgetline(FILE f, char line, size_t len) {
	size_t i = 0;
	int c;
	while((c = fgetc(f)) != '\n') {
	if(c == EOF) {
	if(!i) return -1;
	break;
	}
	if(i >= len - 1) return -2;
	line[i++] = c;
	}
	line[i] = 0;
	return i;
	}

	static int read_user_info(FILE f, char name, char *public_key) {
	int i = 0;
	char line[4096];
	while(1) {
	i++;
	int len = fgetline(f, line, sizeof line);
	if(len == -2) {
	int c;
	fprintf(stderr, "Warning: line %u in file " USER_LIST_FILE " is too long, skipping\n", i);
	while((c = fgetc(f)) != EOF && c != '\n');
	continue;
	}
	if(len < 0) return -1; // EOF
	if(len == 0 \|\| *line == '#') continue;
	char *p = line;
	while(p && (p == ' ' \|\| *p == ' ')) p++;
	if(!*p) continue;
	char *q1 = strchr(p, '"');
	if(!q1) {
	fprintf(stderr, "Warning: cannot find '\"' at line %u in file " USER_LIST_FILE "\n", i);
	continue;
	}
	*q1 = 0;
	if(q1 - p < 8 \|\| strcmp(q1 - 8, "command=") \|\| strchr(p, ' ')) {
	fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", i);
	continue;
	}
	q1++;
	char *q2 = strchr(q1, '"');
	if(!q2) {
	fprintf(stderr, "Warning: unmatched '\"' in file " USER_LIST_FILE " line %u\n", i);
	continue;
	}
	char *space = strchr(q2 + 1, ' ');
	if(!space) {
	fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", i);
	continue;
	}
	size_t user_name_len = q2 - q1;
	if(!user_name_len) {
	fprintf(stderr, "Warning: empty user name in file " USER_LIST_FILE " line %u\n", i);
	continue;
	}
	*name = malloc(user_name_len + 1);
	if(!*name) {
	fprintf(stderr, "Error: allocate %zu bytes failed when processing file " USER_LIST_FILE " line %u\n", user_name_len + 1, i);
	return -1;
	}
	memcpy(*name, q1, user_name_len);
	(*name)[user_name_len] = 0;
	*public_key = strdup(space + 1);
	if(!*public_key) {
	fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", i);
	return -1;
	}
	return 0;
	}
	}

	static int remove_ssh_rc_file() {
	struct stat st;
	if(lstat(".ssh/rc", &st) < 0) {
	if(errno == ENOENT) return 0;
	perror(".ssh/rc");
	return -1;
	}
	if(S_ISDIR(st.st_mode)) {
	fputs("'.ssh/rc' exists, and it is a directory!\n", stderr);
	return -1;
	}
	fputs("sshout shouldn't have a SSH RC file '.ssh/rc'; removing\n", stderr);
	if(unlink(".ssh/rc") < 0) {
	perror("unlink: .ssh/rc");
	return -1;
	}
	return 0;
	}

	static int adduser_command(int argc, char **argv) {
	char *key = NULL;
	int force = 0;
	while(1) {
	int c = getopt(argc, argv, "a:fh");
	if(c == -1) break;
	switch(c) {
	case 'a':
	key = strdup(optarg);
	if(!key) {
	perror("strdup");
	return 1;
	}
	break;
	case 'f':
	force = 1;
	break;
	case 'h':
	print_usage(argv[0]);
	return 0;
	case '?':
	return -1;
	}
	}
	//fprintf(stderr, "optind = %d, argc = %d\n", optind, argc);
	if(argc - optind != 1) {
	print_usage(argv[0]);
	return -1;
	}
	const char *user = argv[optind];
	if(!key) {
	key = malloc(4096);
	if(!key) {
	perror("malloc");
	return 1;
	}
	fprintf(stderr, "Input public key for %s: ", user);
	if(fgetline(stdin, key, 4096) == -2) {
	free(key);
	fputs("Public key too long\n", stderr);
	return 1;
	}
	}

	// TODO: verify the key format

	struct stat st;
	if(stat(".ssh", &st) == 0) {
	if(!S_ISDIR(st.st_mode)) {
	free(key);
	fputs("'.ssh' is not a directory\n", stderr);
	return 1;
	}
	uid_t myuid = getuid();
	if(st.st_uid != myuid) {
	free(key);
	fprintf(stderr, "'.ssh' is not owned by sshout (%u != %u)\n", st.st_uid, myuid);
	return 1;
	}
	if(st.st_mode & S_IWOTH) {
	fputs("'.ssh' is global writable\n", stderr);
	if(chmod(".ssh", st.st_mode & ~(S_IWOTH)) < 0) {
	perror("chmod: .ssh");
	free(key);
	return 1;
	}
	fputs("fixed\n", stderr);
	}
	if(remove_ssh_rc_file() < 0) {
	free(key);
	fputs("Cannot continue\n", stderr);
	return 1;
	}
	} else if(mkdir(".ssh", 0755) < 0) {
	perror("mkdir: .ssh");
	free(key);
	return 1;
	}

	FILE *f = fopen(USER_LIST_FILE, "a+");
	if(!f) {
	perror(USER_LIST_FILE);
	free(key);
	return 1;
	}

	int existing_count = 0;
	{
	char user_name, public_key;
	while(read_user_info(f, &user_name, &public_key) == 0) {
	if(strcmp(key, public_key) == 0) {
	free(key);
	fprintf(stderr, "This public key is already used by user %s.\n"
	"Are you pasted wrong key?\n", user_name);
	free(user_name);
	free(public_key);
	return 1;
	}
	if(strcmp(user, user_name) == 0) existing_count++;
	free(user_name);
	free(public_key);
	}
	}
	if(existing_count) {
	fprintf(stderr, "%d key%s already exist for user %s\n", existing_count, existing_count > 1 ? "s" : "", user);
	if(!force) {
	char answer[16];
	fprintf(stderr, "Are you sure you want to add this key for user %s? ", user);
	do {
	int len = fgetline(stdin, answer, sizeof answer);
	// Ignore line too long error
	if(len == -1 \|\| strncasecmp(answer, "no", 2) == 0 \|\| strncmp(answer, "不", 3) == 0 \|\| strcmp(answer, "否") == 0) {
	fputs("Operation canceled\n", stderr);
	free(key);
	return 1;
	}
	} while(strncasecmp(answer, "yes", 3) && strncmp(answer, "是", 3) && strncmp(answer, "好", 3) && strcmp(answer, "可以"));
	}
	}

	if(fprintf(f, "command=\"%s\",no-agent-forwarding,no-port-forwarding %s\n", user, key) < 0) {
	perror("fprintf");
	free(key);
	return 1;
	}
	free(key);
	return -1;
	}

	static int listuser_command(int argc, char **argv) {
	if(remove_ssh_rc_file() < 0) {
	fputs("Warning: configuration error left unresolved\n", stderr);
	}

	FILE *f = fopen(USER_LIST_FILE, "r");
	if(!f) {
	perror(USER_LIST_FILE);
	return 1;
	}

	/*
	char line[4096];
	while(fgetline(f, line, sizeof line) > 0) {
	fprintf(stderr, "line = \"%s\"\n", line);
	}
	*/
	char user_name, public_key;
	while(read_user_info(f, &user_name, &public_key) == 0) {
	fprintf(stderr, "User \"%s\", Public key \"%s\"\n", user_name, public_key);
	free(user_name);
	free(public_key);
	}
	return 0;
	}

	static int getmotd_command(int argc, char **argv) {
	char buffer[4096];
	int fd = open(SSHOUT_MOTD_FILE, O_RDONLY);
	if(fd == -1) {
	perror(SSHOUT_MOTD_FILE);
	return 1;
	}
	while(1) {
	int s = sync_read(fd, buffer, sizeof buffer);
	if(s < 0) {
	perror("read");
	return 1;
	}
	if(!s) return 0;
	s = sync_write(STDOUT_FILENO, buffer, s);
	if(s < 0) {
	perror("write");
	return 1;
	}
	}
	}

	static int setmotd_command(int argc, char **argv) {
	const char *message = NULL;
	int need_del = 0;
	while(1) {
	int c = getopt(argc, argv, "m:dh");
	if(c == -1) break;
	switch(c) {
	case 'm':
	message = optarg;
	break;
	case 'd':
	need_del = 1;
	break;
	case 'h':
	print_usage(argv[0]);
	return 0;
	case '?':
	return -1;
	}
	}
	if(need_del) {
	if(message) {
	fputs("Option '-d' cannot be used together with '-m'\n", stderr);
	return -1;
	}
	if(unlink(SSHOUT_MOTD_FILE) < 0) {
	perror(SSHOUT_MOTD_FILE);
	return 1;
	}
	return 0;
	}
	int fd = creat(SSHOUT_MOTD_FILE, 0600);
	if(fd == -1) {
	perror(SSHOUT_MOTD_FILE);
	return 1;
	}
	if(message) {
	size_t len = strlen(message);
	int s = sync_write(fd, message, len);
	if(s < 0) {
	perror("write");
	return 1;
	}
	if(len && message[len - 1] != '\n') {
	char new_line = '\n';
	if(sync_write(fd, &new_line, 1) < 0) {
	perror("write");
	return 1;
	}
	}
	return 0;
	} else {
	char buffer[4096];
	if(isatty(STDIN_FILENO)) fputs("Type message below:\n", stderr);
	while(1) {
	int s = read(STDIN_FILENO, buffer, sizeof buffer);
	if(s < 0) {
	if(errno == EINTR) continue;
	perror("read");
	return 1;
	}
	if(!s) return 0;
	s = sync_write(fd, buffer, s);
	if(s < 0) {
	perror("write");
	return 1;
	}
	}
	}
	}

	static struct subcommand {
	const char *name;
	const char *usage;
	int (func)(int, char *);
	} commands[] = {
	#define SUBCOMMAND(N,U) { #N, U, N##_command }
	SUBCOMMAND(adduser, "[-a <public-key-in-base64>] [-f] <user-name>"),
	SUBCOMMAND(listuser, ""),
	SUBCOMMAND(getmotd, ""),
	SUBCOMMAND(setmotd, "[-m <message> \| -d]"),
	#undef SUBCOMMAND
	{ NULL, NULL }
	};

	static void print_commands() {
	struct subcommand *c = commands;
	fputs("Following subcommands are available:\n", stderr);
	while(c->name) {
	fprintf(stderr, " %s %s\n", c->name, c->usage);
	c++;
	}
	}

	static void print_usage(const char *name) {
	struct subcommand *c = commands;
	while(c->name) {
	if(strcmp(c->name, name) == 0) {
	fprintf(stderr, "Usage: %s %s\n", name, c->usage);
	return;
	}
	c++;
	}
	fprintf(stderr, "Error: cannot find usage for command '%s'", name);
	}

	int main(int argc, char **argv) {
	struct passwd *pw = getpwnam("sshout");
	if(!pw) {
	fputs("sshout user account not exist\n", stderr);
	return 1;
	}
	if(pw->pw_uid == 0) {
	fputs("sshout user account have UID 0\n", stderr);
	return 1;
	}

	if(argc < 2) {
	print_commands();
	return -1;
	}

	uid_t myeuid = geteuid();
	if(myeuid == 0) {
	if(setreuid(pw->pw_uid, pw->pw_uid) < 0) {
	perror("setreuid");
	return 1;
	}
	} else if(myeuid != pw->pw_uid) {
	fprintf(stderr, "Current effective UID %u doesn't equal to sshout user account\n", myeuid);
	return 1;
	}

	const char *home = pw->pw_dir;
	struct stat st;
	if(stat(home, &st) < 0) {
	perror(home);
	return 1;
	}
	if(st.st_uid != pw->pw_uid) {
	fprintf(stderr, "Home directory '%s' is not owned by sshout (expecting UID=%u, got %u)\n", home, pw->pw_uid, st.st_uid);
	return 1;
	}
	setenv("HOME", home, 1);
	if(chdir(home) < 0) {
	perror(home);
	return 1;
	}

	struct subcommand *c = commands;
	while(c->name) {
	if(strcmp(argv[1], c->name) == 0) return c->func(argc - 1, argv + 1);
	c++;
	}
	fprintf(stderr, "Unknown command '%s'\n", argv[1]);
	print_commands();
	return -1;
	}