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

 /* Secure Shout Host Oriented Unified Talk
  * 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 "base64.h"
 #include "misc.h"
 #include <unistd.h>
 #include <fcntl.h>
 #include <pwd.h>
 #include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include "file-helpers.h"
 #include <errno.h>
 #include <sys/stat.h>
 #include <arpa/inet.h>
 #include <mhash.h>

 static void print_usage(const char *);

 static enum key_types {
 	KEY_INVALID = -1,
 	KEY_RSA,
 	KEY_DSA,
 	KEY_ECDSA,
 	KEY_ED25519
 } get_key_type(const char *key, size_t type_len) {
 	switch(type_len) {
 		case 3:
 			if(strncasecmp(key, "RSA", 3) == 0) return KEY_RSA;
 			if(strncasecmp(key, "DSA", 3) == 0) return KEY_DSA;
 			return KEY_INVALID;
 		case 5:
 			if(strncasecmp(key, "ECDSA", 5) == 0) return KEY_ECDSA;
 			return KEY_INVALID;
 		case 7:
 			if(strncasecmp(key, "ED25519", 7) == 0) return KEY_ED25519;
 			if(memcmp(key, "ssh-rsa", 7) == 0) return KEY_RSA;
 			if(memcmp(key, "ssh-dss", 7) == 0) return KEY_DSA;
 			return KEY_INVALID;
 		case 11:
 			if(memcmp(key, "ssh-ed25519", 11) == 0) return KEY_ED25519;
 			return KEY_INVALID;
 		case 19:
 			if(memcmp(key, "ecdsa-sha2-nistp", 16) == 0) {
 				if(memcmp(key + 16, "256", 3) == 0 ||
 				   memcmp(key + 16, "384", 3) == 0 ||
 				   memcmp(key + 16, "521", 3) == 0) {
 					return KEY_ECDSA;
 				}
 			}
 			return KEY_INVALID;
 	}
 	return KEY_INVALID;
 }

 static const char *key_type_to_string(enum key_types t) {
 	switch(t) {
 		case KEY_RSA: return "RSA";
 		case KEY_DSA: return "DSA";
 		case KEY_ECDSA: return "ECDSA";
 		case KEY_ED25519: return "ED25519";
 		default: return NULL;
 	}
 }

 static int get_length_and_type_string_length_of_key_in_base64(const char *key, size_t *base64_len, size_t *type_len, char *buffer, size_t buffer_size) {
 #if 0
 	const char *space = strchr(key, ' ');
 	*base64_len = space ? space - key : strlen(key);
 #else
 	*base64_len = 0;
 	while(key[*base64_len] && key[*base64_len] != ' ') (*base64_len)++;
 #endif
 	int blob_len = base64_decode(key, *base64_len, buffer, buffer_size);
 	if(blob_len == -1) {
 		fputs("Invalid key: invalid BASE64 encoding\n", stderr);
 		return -1;
 	}
 	if(blob_len < 4) {
 		fputs("Invalid key: too short\n", stderr);
 		return -1;
 	}
 	*type_len = ntohl(*(uint32_t *)buffer);
 	if(*type_len > (size_t)blob_len - 4) {
 		fprintf(stderr, "Invalid key: key type string length %u too long\n", (unsigned int)*type_len);
 		return -1;
 	}
 	return 0;
 }

 static unsigned int nlines;

 static int read_user_info(FILE *f, char **name, char **public_key, char **comment, enum key_types *key_type, size_t *line_len) {
 	char line[4096];
 	while(1) {
 		nlines++;
 		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", nlines);
 			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", nlines);
 			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", nlines);
 			continue;
 		}
 		q1++;
 		char *q2 = strchr(q1, '"');
 		if(!q2) {
 			fprintf(stderr, "Warning: unmatched '\"' in file " USER_LIST_FILE " line %u\n", nlines);
 			continue;
 		}
 		char *space = strchr(q2 + 1, ' ');
 		if(!space) {
 			fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", nlines);
 			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", nlines);
 			continue;
 		}
 		char *type_string = space + 1;
 		space = strchr(type_string, ' ');
 		if(!space) {
 			fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", nlines);
 			continue;
 		}
 		size_t type_len = space - type_string;
 		enum key_types key_type_1 = get_key_type(type_string, type_len);
 		if(key_type_1 == KEY_INVALID) {
 			*space = 0;
 			fprintf(stderr, "Warning: invalid key type '%s' in file " USER_LIST_FILE " line %u\n", type_string, nlines);
 			continue;
 		}
 		const char *base64 = space + 1;
 		char buffer[32];
 		size_t base64_len, inner_type_len;
 		if(get_length_and_type_string_length_of_key_in_base64(base64, &base64_len, &inner_type_len, buffer, sizeof buffer) < 0) return 1;
 		char *inner_key_type_string = buffer + 4;
 		enum key_types key_type_2 = get_key_type(inner_key_type_string, inner_type_len);
 		if(key_type_2 == KEY_INVALID) {
 			inner_key_type_string[inner_type_len] = 0;
 			fprintf(stderr, "Warning: invalid key type '%s' from BASE64 in file " USER_LIST_FILE " line %u\n", inner_key_type_string, nlines);
 			continue;
 		}
 		if(key_type_2 != key_type_1) {
 			fprintf(stderr, "Warning: key type didn't match in file " USER_LIST_FILE " line %u; key ignored\n", nlines);
 			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, nlines);
 			return -1;
 		}
 		memcpy(*name, q1, user_name_len);
 		(*name)[user_name_len] = 0;
 		*public_key = malloc(type_len + 1 + base64_len + 1);
 		if(!*public_key) {
 			fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", nlines);
 			return -1;
 		}
 		memcpy(*public_key, type_string, type_len + 1 + base64_len);
 		(*public_key)[type_len + 1 + base64_len] = 0;
 		if(comment) {
 			if(base64[base64_len] == ' ') {
 				*comment = strdup(base64 + base64_len + 1);
 				if(!*comment) {
 					fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", nlines);
 					return -1;
 				}
 			} else *comment = NULL;
 		}
 		if(key_type) *key_type = key_type_1;
 		if(line_len) *line_len = len;
 		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 ask_confirm() {
 	char answer[16];
 	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) {
 			return 0;
 		}
 	} while(strncasecmp(answer, "yes", 3) && strncmp(answer, "是", 3) && strncmp(answer, "好", 3) && strcmp(answer, "可以"));
 	return 1;
 }

 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;
 		}
 	}
 	if(argc - optind != 1) {
 		print_usage(argv[0]);
 		return -1;
 	}
 	const char *user = argv[optind];
 	if(!is_valid_user_name(user)) {
 		fprintf(stderr, "Invalid user name '%s'\n", user);
 		return 1;
 	}
 	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;
 		}
 	}

 	size_t type_and_base64_len;
 	char *space = strchr(key, ' ');
 	if(space) {
 		size_t type_len = space - key;
 		enum key_types key_type = get_key_type(key, type_len);
 		if(key_type == KEY_INVALID) {
 			*space = 0;
 			fprintf(stderr, "Invalid key type '%s'\n", key);
 			return 1;
 		}
 		const char *base64 = space + 1;
 		char buffer[32];
 		size_t base64_len, inner_type_len;
 		if(get_length_and_type_string_length_of_key_in_base64(base64, &base64_len, &inner_type_len, buffer, sizeof buffer) < 0) return 1;
 		char *inner_key_type_string = buffer + 4;
 		enum key_types inner_key_type = get_key_type(inner_key_type_string, inner_type_len);
 		if(inner_key_type == KEY_INVALID) {
 			inner_key_type_string[inner_type_len] = 0;
 			fprintf(stderr, "Invalid key type '%s'\n", inner_key_type_string);
 			return 1;
 		}
 		if(inner_key_type != key_type) {
 			fputs("Invalid key: key type didn't match\n", stderr);
 			return 1;
 		}
 		type_and_base64_len = type_len + 1 + base64_len;
 	} else {
 		char buffer[32];
 		size_t base64_len, type_len;
 		if(get_length_and_type_string_length_of_key_in_base64(key, &base64_len, &type_len, buffer, sizeof buffer) < 0) return 1;
 		char *key_type_string = buffer + 4;
 		enum key_types key_type = get_key_type(key_type_string, type_len);
 		if(key_type == KEY_INVALID) {
 			key_type_string[type_len] = 0;
 			fprintf(stderr, "Invalid key type '%s'\n", key_type_string);
 			return 1;
 		}
 		char *type_and_key_in_base64 = malloc(type_len + 1 + base64_len + 1);
 		if(!type_and_key_in_base64) {
 			perror("malloc");
 			return 1;
 		}
 		memcpy(type_and_key_in_base64, key_type_string, type_len);
 		type_and_key_in_base64[type_len] = ' ';
 		memcpy(type_and_key_in_base64 + type_len + 1, key, base64_len);
 		type_and_key_in_base64[type_len + 1 + base64_len] = 0;
 		free(key);
 		key = type_and_key_in_base64;
 		type_and_base64_len = type_len + 1 + base64_len;
 	}

 	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, NULL, NULL, NULL) == 0) {
 			if(strncmp(key, public_key, type_and_base64_len) == 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) {
 			fprintf(stderr, "Are you sure you want to add this key for user %s? ", user);
 			if(!ask_confirm()) {
 				fputs("Operation canceled\n", stderr);
 				free(key);
 				return 1;
 			}
 		}
 	}

 	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 0;
 }

 static int removeuser_command(int argc, char **argv) {
 	int force = 0;
 	while(1) {
 		int c = getopt(argc, argv, "fh");
 		if(c == -1) break;
 		switch(c) {
 			case 'f':
 				force = 1;
 				break;
 			case 'h':
 				print_usage(argv[0]);
 				return 0;
 			case '?':
 				return -1;
 		}
 	}
 	if(argc - optind != 1) {
 		print_usage(argv[0]);
 		return -1;
 	}
 	const char *user = argv[optind];
 	if(!is_valid_user_name(user)) {
 		fprintf(stderr, "Invalid user name '%s'\n", user);
 		return 1;
 	}

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

 	struct line_info {
 		long int end_offset;
 		size_t length;
 	} *match_lines = NULL;
 	size_t line_count = 0, match_lines_allocated_size = 0;
 	char *user_name, *public_key;
 	size_t line_len;
 	while(read_user_info(f, &user_name, &public_key, NULL, NULL, &line_len) == 0) {
 		if(strcmp(user, user_name) == 0) {
 			if(line_count * sizeof(struct line_info) >= match_lines_allocated_size) {
 				match_lines = realloc(match_lines, match_lines_allocated_size += 2 * sizeof(struct line_info));
 				if(!match_lines) {
 					perror("realloc");
 					return 1;
 				}
 			}
 			match_lines[line_count].end_offset = ftell(f);
 			match_lines[line_count].length = line_len;
 			line_count++;
 		}
 		free(user_name);
 		free(public_key);
 	}

 	if(!line_count) {
 		fclose(f);
 		fprintf(stderr, "User %s not found\n", user);
 		return 1;
 	}

 	if(line_count == 1) {
 		if(!force) {
 			fprintf(stderr, "Remove user %s from SSHOUT user list? ", user);
 			if(!ask_confirm()) {
 				fclose(f);
 				fputs("Operation canceled\n", stderr);
 				return 1;
 			}
 		}
 		if(fseek(f, match_lines->end_offset, SEEK_SET) < 0 ||
 		fbackwardoverwrite(f, match_lines->length + 1) < 0) {
 			perror("Failed to remove user");
 			fclose(f);
 			return 1;
 		}
 		if(fclose(f) == EOF) {
 			perror("fclose");
 			return 1;
 		}
 		return 0;
 	} else {
 		if(!force) {
 			fprintf(stderr, "User %s have %zu public keys registered in the user list\n", user, line_count);
 			fprintf(stderr, "If you want to remove only some of the user's keys, edit file '%s/ " USER_LIST_FILE "' manually\n",
 				getenv("HOME"));
 			fprintf(stderr, "Remove all keys for user %s? ", user);
 			if(!ask_confirm()) {
 				fclose(f);
 				fputs("Operation canceled\n", stderr);
 				return 1;
 			}
 		}
 		unsigned int i = line_count;
 		do {
 			i--;
 			if(fseek(f, match_lines[i].end_offset, SEEK_SET) < 0 ||
 			fbackwardoverwrite(f, match_lines[i].length + 1) < 0) {
 				perror("Failed to remove user");
 				fprintf(stderr, "when removing key %u from user list\n", i);
 				fclose(f);
 				return 1;
 			}
 		} while(i > 0);
 		if(fclose(f) == EOF) {
 			perror("fclose");
 			return 1;
 		}
 		fprintf(stderr, "Removed %zu keys for user %s\n", line_count, user);
 		return 0;
 	}
 }

 static int listuser_command(int argc, char **argv) {
 	hashid hash_type = -1;
 	while(1) {
 		int c = getopt(argc, argv, "h:");
 		if(c == -1) break;
 		switch(c) {
 			case 'h':
 				if(strcmp(optarg, "md5") == 0) hash_type = MHASH_MD5;
 				else if(strcmp(optarg, "sha256") == 0) hash_type = MHASH_SHA256;
 				else {
 					fprintf(stderr, "Invalid hash algorithm '%s'\n", optarg);
 					return -1;
 				}
 				break;
 			case '?':
 				print_usage(argv[0]);
 				return -1;
 		}
 	}

 	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 *user_name, *public_key, *comment;
 	while(read_user_info(f, &user_name, &public_key, &comment, NULL, NULL) == 0) {
 		//printf("User \"%s\", Public key \"%s\"", user_name, public_key);
 		printf("User \"%s\", ", user_name);
 		if((int)hash_type == -1) {
 			printf("Public key \"%s\"", public_key);
 		} else {
 			MHASH h = mhash_init(hash_type);
 			if(h == MHASH_FAILED) {
 				fputs("Cannot start hash public key\n", stderr);
 				return 1;
 			}
 			char *space = strchr(public_key, ' ');
 			if(!space) {
 				fputs("Invalid key\n", stderr);
 				return 1;
 			}
 			char *base64 = space + 1;
 			int len = strlen(base64);
 			char buffer[len];
 			len = base64_decode(base64, len, buffer, sizeof buffer);
 			if(len < 0) {
 				fputs("Invalid BASE64 encoding\n", stderr);
 				return 1;
 			}
 			if(len < 8) {
 				fputs("Invalid key\n", stderr);
 				return 1;
 			}
 			size_t type_len = ntohl(*(uint32_t *)buffer);
 			if(type_len > len - 4) {
 				fputs("Invalid key\n", stderr);
 				return 1;
 			}
 			printf("Public key fingerprint %s ", key_type_to_string(get_key_type(buffer + 4, type_len)));
 			mhash(h, buffer, len);
 			unsigned char *hash = mhash_end(h);
 			unsigned int i = 0, hash_len = mhash_get_block_size(hash_type);
 			if(hash_type == MHASH_SHA256) {
 				char buffer[44];
 				len = base64_encode(hash, hash_len, buffer, sizeof buffer, 0);
 				fputs(len < 0 ? "Cannot encode SHA-256 fingerprint" : buffer, stdout);
 			} else while(i < hash_len) {
 				if(i) putchar(':');
 				printf("%.2hhx", hash[i++]);
 			}
 		}
 		if(comment) printf(", Comment \"%s\"", comment);
 		putchar('\n');
 		free(user_name);
 		free(public_key);
 		free(comment);
 	}
 	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 '?':
 				print_usage(argv[0]);
 				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(removeuser, "[-f] <user-name>"),
 	SUBCOMMAND(listuser, "[-h {md5|sha256}]"),
 	SUBCOMMAND(getmotd, ""),
 	SUBCOMMAND(setmotd, "[-m <message> | -d]"),
 #undef SUBCOMMAND
 	{ NULL, 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;
 }
	/* Secure Shout Host Oriented Unified Talk
	* 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 "base64.h"
	#include "misc.h"
	#include <unistd.h>
	#include <fcntl.h>
	#include <pwd.h>
	#include <string.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include "file-helpers.h"
	#include <errno.h>
	#include <sys/stat.h>
	#include <arpa/inet.h>
	#include <mhash.h>

	static void print_usage(const char *);

	static enum key_types {
	KEY_INVALID = -1,
	KEY_RSA,
	KEY_DSA,
	KEY_ECDSA,
	KEY_ED25519
	} get_key_type(const char *key, size_t type_len) {
	switch(type_len) {
	case 3:
	if(strncasecmp(key, "RSA", 3) == 0) return KEY_RSA;
	if(strncasecmp(key, "DSA", 3) == 0) return KEY_DSA;
	return KEY_INVALID;
	case 5:
	if(strncasecmp(key, "ECDSA", 5) == 0) return KEY_ECDSA;
	return KEY_INVALID;
	case 7:
	if(strncasecmp(key, "ED25519", 7) == 0) return KEY_ED25519;
	if(memcmp(key, "ssh-rsa", 7) == 0) return KEY_RSA;
	if(memcmp(key, "ssh-dss", 7) == 0) return KEY_DSA;
	return KEY_INVALID;
	case 11:
	if(memcmp(key, "ssh-ed25519", 11) == 0) return KEY_ED25519;
	return KEY_INVALID;
	case 19:
	if(memcmp(key, "ecdsa-sha2-nistp", 16) == 0) {
	if(memcmp(key + 16, "256", 3) == 0 \|\|
	memcmp(key + 16, "384", 3) == 0 \|\|
	memcmp(key + 16, "521", 3) == 0) {
	return KEY_ECDSA;
	}
	}
	return KEY_INVALID;
	}
	return KEY_INVALID;
	}

	static const char *key_type_to_string(enum key_types t) {
	switch(t) {
	case KEY_RSA: return "RSA";
	case KEY_DSA: return "DSA";
	case KEY_ECDSA: return "ECDSA";
	case KEY_ED25519: return "ED25519";
	default: return NULL;
	}
	}

	static int get_length_and_type_string_length_of_key_in_base64(const char key, size_t base64_len, size_t type_len, char buffer, size_t buffer_size) {
	#if 0
	const char *space = strchr(key, ' ');
	*base64_len = space ? space - key : strlen(key);
	#else
	*base64_len = 0;
	while(key[base64_len] && key[base64_len] != ' ') (*base64_len)++;
	#endif
	int blob_len = base64_decode(key, *base64_len, buffer, buffer_size);
	if(blob_len == -1) {
	fputs("Invalid key: invalid BASE64 encoding\n", stderr);
	return -1;
	}
	if(blob_len < 4) {
	fputs("Invalid key: too short\n", stderr);
	return -1;
	}
	type_len = ntohl((uint32_t *)buffer);
	if(*type_len > (size_t)blob_len - 4) {
	fprintf(stderr, "Invalid key: key type string length %u too long\n", (unsigned int)*type_len);
	return -1;
	}
	return 0;
	}

	static unsigned int nlines;

	static int read_user_info(FILE f, char name, char public_key, char comment, enum key_types key_type, size_t *line_len) {
	char line[4096];
	while(1) {
	nlines++;
	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", nlines);
	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", nlines);
	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", nlines);
	continue;
	}
	q1++;
	char *q2 = strchr(q1, '"');
	if(!q2) {
	fprintf(stderr, "Warning: unmatched '\"' in file " USER_LIST_FILE " line %u\n", nlines);
	continue;
	}
	char *space = strchr(q2 + 1, ' ');
	if(!space) {
	fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", nlines);
	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", nlines);
	continue;
	}
	char *type_string = space + 1;
	space = strchr(type_string, ' ');
	if(!space) {
	fprintf(stderr, "Warning: syntax error in file " USER_LIST_FILE " line %u\n", nlines);
	continue;
	}
	size_t type_len = space - type_string;
	enum key_types key_type_1 = get_key_type(type_string, type_len);
	if(key_type_1 == KEY_INVALID) {
	*space = 0;
	fprintf(stderr, "Warning: invalid key type '%s' in file " USER_LIST_FILE " line %u\n", type_string, nlines);
	continue;
	}
	const char *base64 = space + 1;
	char buffer[32];
	size_t base64_len, inner_type_len;
	if(get_length_and_type_string_length_of_key_in_base64(base64, &base64_len, &inner_type_len, buffer, sizeof buffer) < 0) return 1;
	char *inner_key_type_string = buffer + 4;
	enum key_types key_type_2 = get_key_type(inner_key_type_string, inner_type_len);
	if(key_type_2 == KEY_INVALID) {
	inner_key_type_string[inner_type_len] = 0;
	fprintf(stderr, "Warning: invalid key type '%s' from BASE64 in file " USER_LIST_FILE " line %u\n", inner_key_type_string, nlines);
	continue;
	}
	if(key_type_2 != key_type_1) {
	fprintf(stderr, "Warning: key type didn't match in file " USER_LIST_FILE " line %u; key ignored\n", nlines);
	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, nlines);
	return -1;
	}
	memcpy(*name, q1, user_name_len);
	(*name)[user_name_len] = 0;
	*public_key = malloc(type_len + 1 + base64_len + 1);
	if(!*public_key) {
	fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", nlines);
	return -1;
	}
	memcpy(*public_key, type_string, type_len + 1 + base64_len);
	(*public_key)[type_len + 1 + base64_len] = 0;
	if(comment) {
	if(base64[base64_len] == ' ') {
	*comment = strdup(base64 + base64_len + 1);
	if(!*comment) {
	fprintf(stderr, "Error: out of memory when processing file " USER_LIST_FILE " line %u\n", nlines);
	return -1;
	}
	} else *comment = NULL;
	}
	if(key_type) *key_type = key_type_1;
	if(line_len) *line_len = len;
	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 ask_confirm() {
	char answer[16];
	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) {
	return 0;
	}
	} while(strncasecmp(answer, "yes", 3) && strncmp(answer, "是", 3) && strncmp(answer, "好", 3) && strcmp(answer, "可以"));
	return 1;
	}

	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;
	}
	}
	if(argc - optind != 1) {
	print_usage(argv[0]);
	return -1;
	}
	const char *user = argv[optind];
	if(!is_valid_user_name(user)) {
	fprintf(stderr, "Invalid user name '%s'\n", user);
	return 1;
	}
	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;
	}
	}

	size_t type_and_base64_len;
	char *space = strchr(key, ' ');
	if(space) {
	size_t type_len = space - key;
	enum key_types key_type = get_key_type(key, type_len);
	if(key_type == KEY_INVALID) {
	*space = 0;
	fprintf(stderr, "Invalid key type '%s'\n", key);
	return 1;
	}
	const char *base64 = space + 1;
	char buffer[32];
	size_t base64_len, inner_type_len;
	if(get_length_and_type_string_length_of_key_in_base64(base64, &base64_len, &inner_type_len, buffer, sizeof buffer) < 0) return 1;
	char *inner_key_type_string = buffer + 4;
	enum key_types inner_key_type = get_key_type(inner_key_type_string, inner_type_len);
	if(inner_key_type == KEY_INVALID) {
	inner_key_type_string[inner_type_len] = 0;
	fprintf(stderr, "Invalid key type '%s'\n", inner_key_type_string);
	return 1;
	}
	if(inner_key_type != key_type) {
	fputs("Invalid key: key type didn't match\n", stderr);
	return 1;
	}
	type_and_base64_len = type_len + 1 + base64_len;
	} else {
	char buffer[32];
	size_t base64_len, type_len;
	if(get_length_and_type_string_length_of_key_in_base64(key, &base64_len, &type_len, buffer, sizeof buffer) < 0) return 1;
	char *key_type_string = buffer + 4;
	enum key_types key_type = get_key_type(key_type_string, type_len);
	if(key_type == KEY_INVALID) {
	key_type_string[type_len] = 0;
	fprintf(stderr, "Invalid key type '%s'\n", key_type_string);
	return 1;
	}
	char *type_and_key_in_base64 = malloc(type_len + 1 + base64_len + 1);
	if(!type_and_key_in_base64) {
	perror("malloc");
	return 1;
	}
	memcpy(type_and_key_in_base64, key_type_string, type_len);
	type_and_key_in_base64[type_len] = ' ';
	memcpy(type_and_key_in_base64 + type_len + 1, key, base64_len);
	type_and_key_in_base64[type_len + 1 + base64_len] = 0;
	free(key);
	key = type_and_key_in_base64;
	type_and_base64_len = type_len + 1 + base64_len;
	}

	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, NULL, NULL, NULL) == 0) {
	if(strncmp(key, public_key, type_and_base64_len) == 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) {
	fprintf(stderr, "Are you sure you want to add this key for user %s? ", user);
	if(!ask_confirm()) {
	fputs("Operation canceled\n", stderr);
	free(key);
	return 1;
	}
	}
	}

	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 0;
	}

	static int removeuser_command(int argc, char **argv) {
	int force = 0;
	while(1) {
	int c = getopt(argc, argv, "fh");
	if(c == -1) break;
	switch(c) {
	case 'f':
	force = 1;
	break;
	case 'h':
	print_usage(argv[0]);
	return 0;
	case '?':
	return -1;
	}
	}
	if(argc - optind != 1) {
	print_usage(argv[0]);
	return -1;
	}
	const char *user = argv[optind];
	if(!is_valid_user_name(user)) {
	fprintf(stderr, "Invalid user name '%s'\n", user);
	return 1;
	}

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

	struct line_info {
	long int end_offset;
	size_t length;
	} *match_lines = NULL;
	size_t line_count = 0, match_lines_allocated_size = 0;
	char user_name, public_key;
	size_t line_len;
	while(read_user_info(f, &user_name, &public_key, NULL, NULL, &line_len) == 0) {
	if(strcmp(user, user_name) == 0) {
	if(line_count * sizeof(struct line_info) >= match_lines_allocated_size) {
	match_lines = realloc(match_lines, match_lines_allocated_size += 2 * sizeof(struct line_info));
	if(!match_lines) {
	perror("realloc");
	return 1;
	}
	}
	match_lines[line_count].end_offset = ftell(f);
	match_lines[line_count].length = line_len;
	line_count++;
	}
	free(user_name);
	free(public_key);
	}

	if(!line_count) {
	fclose(f);
	fprintf(stderr, "User %s not found\n", user);
	return 1;
	}

	if(line_count == 1) {
	if(!force) {
	fprintf(stderr, "Remove user %s from SSHOUT user list? ", user);
	if(!ask_confirm()) {
	fclose(f);
	fputs("Operation canceled\n", stderr);
	return 1;
	}
	}
	if(fseek(f, match_lines->end_offset, SEEK_SET) < 0 \|\|
	fbackwardoverwrite(f, match_lines->length + 1) < 0) {
	perror("Failed to remove user");
	fclose(f);
	return 1;
	}
	if(fclose(f) == EOF) {
	perror("fclose");
	return 1;
	}
	return 0;
	} else {
	if(!force) {
	fprintf(stderr, "User %s have %zu public keys registered in the user list\n", user, line_count);
	fprintf(stderr, "If you want to remove only some of the user's keys, edit file '%s/ " USER_LIST_FILE "' manually\n",
	getenv("HOME"));
	fprintf(stderr, "Remove all keys for user %s? ", user);
	if(!ask_confirm()) {
	fclose(f);
	fputs("Operation canceled\n", stderr);
	return 1;
	}
	}
	unsigned int i = line_count;
	do {
	i--;
	if(fseek(f, match_lines[i].end_offset, SEEK_SET) < 0 \|\|
	fbackwardoverwrite(f, match_lines[i].length + 1) < 0) {
	perror("Failed to remove user");
	fprintf(stderr, "when removing key %u from user list\n", i);
	fclose(f);
	return 1;
	}
	} while(i > 0);
	if(fclose(f) == EOF) {
	perror("fclose");
	return 1;
	}
	fprintf(stderr, "Removed %zu keys for user %s\n", line_count, user);
	return 0;
	}
	}

	static int listuser_command(int argc, char **argv) {
	hashid hash_type = -1;
	while(1) {
	int c = getopt(argc, argv, "h:");
	if(c == -1) break;
	switch(c) {
	case 'h':
	if(strcmp(optarg, "md5") == 0) hash_type = MHASH_MD5;
	else if(strcmp(optarg, "sha256") == 0) hash_type = MHASH_SHA256;
	else {
	fprintf(stderr, "Invalid hash algorithm '%s'\n", optarg);
	return -1;
	}
	break;
	case '?':
	print_usage(argv[0]);
	return -1;
	}
	}

	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 user_name, public_key, *comment;
	while(read_user_info(f, &user_name, &public_key, &comment, NULL, NULL) == 0) {
	//printf("User \"%s\", Public key \"%s\"", user_name, public_key);
	printf("User \"%s\", ", user_name);
	if((int)hash_type == -1) {
	printf("Public key \"%s\"", public_key);
	} else {
	MHASH h = mhash_init(hash_type);
	if(h == MHASH_FAILED) {
	fputs("Cannot start hash public key\n", stderr);
	return 1;
	}
	char *space = strchr(public_key, ' ');
	if(!space) {
	fputs("Invalid key\n", stderr);
	return 1;
	}
	char *base64 = space + 1;
	int len = strlen(base64);
	char buffer[len];
	len = base64_decode(base64, len, buffer, sizeof buffer);
	if(len < 0) {
	fputs("Invalid BASE64 encoding\n", stderr);
	return 1;
	}
	if(len < 8) {
	fputs("Invalid key\n", stderr);
	return 1;
	}
	size_t type_len = ntohl((uint32_t )buffer);
	if(type_len > len - 4) {
	fputs("Invalid key\n", stderr);
	return 1;
	}
	printf("Public key fingerprint %s ", key_type_to_string(get_key_type(buffer + 4, type_len)));
	mhash(h, buffer, len);
	unsigned char *hash = mhash_end(h);
	unsigned int i = 0, hash_len = mhash_get_block_size(hash_type);
	if(hash_type == MHASH_SHA256) {
	char buffer[44];
	len = base64_encode(hash, hash_len, buffer, sizeof buffer, 0);
	fputs(len < 0 ? "Cannot encode SHA-256 fingerprint" : buffer, stdout);
	} else while(i < hash_len) {
	if(i) putchar(':');
	printf("%.2hhx", hash[i++]);
	}
	}
	if(comment) printf(", Comment \"%s\"", comment);
	putchar('\n');
	free(user_name);
	free(public_key);
	free(comment);
	}
	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 '?':
	print_usage(argv[0]);
	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(removeuser, "[-f] <user-name>"),
	SUBCOMMAND(listuser, "[-h {md5\|sha256}]"),
	SUBCOMMAND(getmotd, ""),
	SUBCOMMAND(setmotd, "[-m <message> \| -d]"),
	#undef SUBCOMMAND
	{ NULL, 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;
	}