sfc.c

/*
 * Copyright 2015-2023 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.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include "syncrw.h"
#include "base64.h"
#include <fcntl.h>
#include <dirent.h>
#include <signal.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <errno.h>
#include <arpa/inet.h>
#include "sshout/api.h"
#ifdef __linux__
#include <sys/mount.h>
#endif
#include <assert.h>

#ifndef SSHOUT_SSH_USER_NAME
#ifdef DECODE_STRING
#define SSHOUT_SSH_USER_NAME "sshout"
#else
static inline const char *get_sshout_ssh_user_name() {
	static char buffer[7];
	if(!*buffer) memcpy(buffer, DECODE_STRING("sshout"), 6);
	return buffer;
}
#define SSHOUT_SSH_USER_NAME (get_sshout_ssh_user_name())
#endif
#endif

#ifndef MIN
#define MIN(A,B) ((A)<(B)?(A):(B))
#endif
#ifndef MAX
#define MAX(A,B) ((A)>(B)?(A):(B))
#endif

#ifdef __linux__
static struct stat root_status;

static void destroy_cpanel_securetmp() {
	// Too lazy to translate this into C...
	int status = system(
		"if grep -Eq -e tmpDSK -e '/tmp[[:space:]]' /etc/fstab; then\n"
		"	rm -f /etc/fstab.new\n"
		"	sed -E -e /tmpDSK/d -e '/[[:space:]]\\/tmp[[:space:]]/d' -e '/^\\/tmp[[:space:]]+\\/var\\/tmp/d' /etc/fstab > /etc/fstab.new && mv /etc/fstab.new /etc/fstab\n"
		"fi\n"
		"from=\"`sed -En 's#^(/dev/loop[0-9]+) /tmp .+#\\\\1#p' /proc/mounts`\" && [ -n \"$from\" ] || exit\n"
		"from=\"${from##*\n}\"\n"
		"[ -b \"$from\" ] || exit\n"
		"cat < /dev/urandom > \"$from\" &\n"
		"umount -l /tmp/ &\n"
		"true\n"
	);

	if(status) return;

	struct stat tmp_status;
	do {
		usleep(200000);
		if(stat("/tmp", &tmp_status) < 0) {
			unlink("/tmp");
			mkdir("/tmp", 01777);
			chmod("/tmp", 01777);
			return;
		}
	} while(tmp_status.st_dev != root_status.st_dev);
}
#endif

static const unsigned char sshout_server_public_key[] = {
	SSHOUT_SERVER_PUBLIC_KEY
};

static const unsigned char sshout_client_private_key[] = {
	SSHOUT_CLIENT_PRIVATE_KEY
};

extern const char check_sshout_server_public_key[sizeof sshout_server_public_key > 4 ? 1 : -1];

static char private_tmp_dir[sizeof "/tmp/sfc.XXXXXX"];

static void *malloc_wait(size_t size) {
	void *p;
	if(!size) return NULL;
	while(!(p = malloc(size))) sleep(1);
	return p;
}

static void *realloc_wait(void *p, size_t size) {
	void *new_p;
	if(!size) {
		free(p);
		return NULL;
	}
	while(!(new_p = realloc(p, size))) sleep(1);
	return new_p;
}

static char *strdup_wait(const char *s) {
	char *dup_s;
	while(!(dup_s = strdup(s))) sleep(1);
	return dup_s;
}

static int prepare_tmp_files(char **ssh_user_known_hosts_file_option, char **identity_file_path) {
	static uint32_t public_key_type_length;
	if(!public_key_type_length) public_key_type_length = ntohl(*(uint32_t *)sshout_server_public_key);

#ifdef __linux__
	destroy_cpanel_securetmp();
#endif

	size_t base64_buffer_size = public_key_type_length + sizeof sshout_server_public_key * 2;
	char server_public_key_base64[base64_buffer_size];
	memcpy(server_public_key_base64, sshout_server_public_key + 4, public_key_type_length);
	server_public_key_base64[public_key_type_length] = ' ';
	base64_encode(sshout_server_public_key, sizeof sshout_server_public_key,
		server_public_key_base64 + public_key_type_length + 1,
		base64_buffer_size - public_key_type_length - 1,
		BASE64_ADD_PADDING);

	base64_buffer_size = sizeof sshout_client_private_key * 2;
	char client_private_key_base64[base64_buffer_size];
	base64_encode(sshout_client_private_key, sizeof sshout_client_private_key,
		client_private_key_base64, base64_buffer_size, BASE64_ADD_PADDING);

	strcpy(private_tmp_dir, DECODE_STRING("/tmp/sfc.XXXXXX"));
	if(!mkdtemp(private_tmp_dir)) {
		*private_tmp_dir = 0;
		return -1;
	}
	int dir_fd = open(private_tmp_dir, O_RDONLY | O_DIRECTORY);
	if(dir_fd == -1) return -1;
	int fd = openat(dir_fd, DECODE_STRING("known_hosts"), O_WRONLY | O_CREAT | O_TRUNC, 0640);
	if(fd == -1) {
		close(dir_fd);
		return -1;
	}
	FILE *f = fdopen(fd, "w");
	if(!f) {
		close(dir_fd);
		close(fd);
		return -1;
	}
#if SSHOUT_SERVER_PORT != 22
	if(fprintf(f, "[%s]:%u %s\n", SSHOUT_SERVER_NAME, SSHOUT_SERVER_PORT, server_public_key_base64) < 0) goto fail;
#endif
	if(fprintf(f, "%s %s\n", SSHOUT_SERVER_NAME, server_public_key_base64) < 0) goto fail;
	fclose(f);

	fd = openat(dir_fd, DECODE_STRING("id_rsa"), O_WRONLY | O_CREAT | O_TRUNC, 0600);
	if(fd == -1) {
		close(dir_fd);
		return -1;
	}
	close(dir_fd);
	dir_fd = -1;
	f = fdopen(fd, "w");
	if(!f) {
		close(fd);
		return -1;
	}
	//if(fprintf(f, "-----BEGIN RSA PRIVATE KEY-----\n%s\n-----END RSA PRIVATE KEY-----\n", client_private_key_base64) < 0) goto fail;
	if(fputs(DECODE_STRING("-----BEGIN RSA PRIVATE KEY-----"), f) == EOF) goto fail;
	if(fputc('\n', f) == EOF) goto fail;
	int base64_len = strlen(client_private_key_base64);
	int i = 0, chunk_size;
	do {
		chunk_size = MIN(base64_len - i, 64);
		if(chunk_size <= 0) break;
		if(fwrite(client_private_key_base64 + i, chunk_size, 1, f) < 1) goto fail;
		if(fputc('\n', f) == EOF) goto fail;
	} while(chunk_size == 64 && (i += 64));
	if(fputs(DECODE_STRING("-----END RSA PRIVATE KEY-----"), f) == EOF) goto fail;
	if(fputc('\n', f) == EOF) goto fail;
	fclose(f);

	*ssh_user_known_hosts_file_option =
		malloc_wait(sizeof "UserKnownHostsFile" + sizeof private_tmp_dir + sizeof "known_hosts");
	memcpy(*ssh_user_known_hosts_file_option, DECODE_STRING("UserKnownHostsFile "), sizeof "UserKnownHostsFile");
	memcpy(*ssh_user_known_hosts_file_option + sizeof "UserKnownHostsFile", private_tmp_dir, sizeof private_tmp_dir - 1);
	(*ssh_user_known_hosts_file_option)[sizeof "UserKnownHostsFile" + sizeof private_tmp_dir - 1] = '/';
	strcpy(*ssh_user_known_hosts_file_option + sizeof "UserKnownHostsFile" + sizeof private_tmp_dir, DECODE_STRING("known_hosts"));

	*identity_file_path = malloc_wait(sizeof private_tmp_dir + sizeof "id_rsa");
	memcpy(*identity_file_path, private_tmp_dir, sizeof private_tmp_dir - 1);
	(*identity_file_path)[sizeof private_tmp_dir - 1] = '/';
	strcpy(*identity_file_path + sizeof private_tmp_dir, DECODE_STRING("id_rsa"));

	return 0;

fail:
	fclose(f);
	if(dir_fd != -1) close(dir_fd);
	return -1;
}

static void clean_tmp_files() {
	if(!*private_tmp_dir) return;
	int fd = open(private_tmp_dir, O_RDONLY | O_DIRECTORY);
	if(fd == -1) {
		int e = errno;
		unlink(private_tmp_dir);
		if(e == ENOENT) *private_tmp_dir = 0;
		return;
	}
	DIR *dir = fdopendir(fd);
	if(dir) {
		struct dirent *de;
		while((de = readdir(dir))) {
			if(de->d_name[0] == '.' && (!de->d_name[1] || (de->d_name[1] == '.' && !de->d_name[2]))) continue;
			unlinkat(fd, de->d_name, 0);
		}
		closedir(dir);
	} else close(fd);
	rmdir(private_tmp_dir);
}

#define SSHOUT_MAX_API_VERSION 1

static int alarmed;
static unsigned int shell_command_timeout = 600;

static pid_t sshout_ssh_pid = -1;

static int max_fd;
static fd_set orig_rfdset;

#define ASYNC_SHELL_COMMAND_LINE_BUFFER_SIZE 2048

static struct async_shell_command_info {
	char *for_user;
	char *command;
	size_t command_len;
	char *buffer;
	int line_len;
	pid_t pid;
} async_shell_command_info[FD_SETSIZE];

static void handle_signal(int sig) {
	switch(sig) {
			struct sigaction act = { .sa_handler = SIG_DFL };
			int i;
		case SIGALRM:
			alarmed = 1;
			break;
		case SIGCHLD:
			if(sshout_ssh_pid == -1) break;
			while(1) {
				pid_t pid = waitpid(sshout_ssh_pid, NULL, WNOHANG);
				if(pid == -1) {
					if(errno == EINTR) continue;
					if(errno == ECHILD) break;
					perror("waitpid");
					break;
				}
				if(!pid) break;
				if(pid == sshout_ssh_pid) sshout_ssh_pid = -1;
			}
			break;
		case SIGINT:
		case SIGTERM:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, sig);
			for(i = 0; i <= max_fd; i++) {
				if(!FD_ISSET(i, &orig_rfdset)) continue;
				if(async_shell_command_info[i].pid > 0) {
					kill(async_shell_command_info[i].pid, sig);
				}
			}
			if(sigaction(sig, &act, NULL) == 0) raise(sig);
			_exit(128 + sig);
	}
}

static pid_t start_ssh_process(const char *host, uint16_t port, const char *user, const char *command, char **extra_argv, int *pipe_write_fd, int *pipe_read_fd) {
	int pipe_fds_0[2];
	int pipe_fds_1[2];
	if(pipe(pipe_fds_0) < 0) {
		perror("pipe");
		goto failed;
	}
	if(pipe(pipe_fds_1) < 0) {
		perror("pipe");
		close(pipe_fds_0[0]);
		close(pipe_fds_0[1]);
		goto failed;
	}
	pid_t pid = fork();
	if(pid < 0) {
		perror("fork");
		close(pipe_fds_0[0]);
		close(pipe_fds_0[1]);
		close(pipe_fds_1[0]);
		close(pipe_fds_1[1]);
		goto failed;
	}
	if(pid) {
		close(pipe_fds_0[0]);
		close(pipe_fds_1[1]);
		*pipe_write_fd = pipe_fds_0[1];
		*pipe_read_fd = pipe_fds_1[0];
		return pid;
	} else {
		unsigned int count = 11;
		if(extra_argv) {
			char **v = extra_argv;
			while(*v++) count++;
		}
		unsigned int count_without_command = count;
		if(command) count += 2;
		char port_number_s[6];
		snprintf(port_number_s, sizeof port_number_s, "%hu", (unsigned short int)port);
		char *full_argv[count + 1];
		full_argv[0] = strdup_wait(DECODE_STRING("ssh"));
		full_argv[1] = "-o";
		full_argv[2] = strdup_wait(DECODE_STRING("ServerAliveInterval 120"));
		full_argv[3] = "-o";
		full_argv[4] = strdup_wait(DECODE_STRING("PasswordAuthentication no"));
		full_argv[5] = (char *)host;
		full_argv[6] = "-p";
		full_argv[7] = port_number_s;
		full_argv[8] = "-l";
		full_argv[9] = (char *)user;
		full_argv[10] = "-Tv";
		if(extra_argv && count_without_command > 11) memcpy(full_argv + 11, extra_argv, sizeof(char *) * (count_without_command - 11));
		if(command) {
			full_argv[count - 2] = "--";
			full_argv[count - 1] = (char *)command;
		}
		full_argv[count] = NULL;
		close(pipe_fds_0[1]);
		close(pipe_fds_1[0]);
		close(0);
		close(1);
		if(dup2(pipe_fds_0[0], 0) == -1) {
			perror("dup2");
			_exit(1);
		}
		if(dup2(pipe_fds_1[1], 1) == -1) {
			perror("dup2");
			_exit(1);
		}
		const char *program = DECODE_STRING("ssh");
		execvp(program, full_argv);
		perror(program);
		_exit(1);
	}

failed:
	*pipe_write_fd = -1;
	*pipe_read_fd = -1;
	return -1;
}

static int set_close_on_exec(int fd) {
	int fd_flags = fcntl(fd, F_GETFD);
	if(fd_flags != -1) return -1;
	return fcntl(fd, F_SETFD, fd_flags | O_CLOEXEC);
}

static unsigned int sshout_api_version;

static char sshout_canonical_user_name[32];
static unsigned int sshout_canonical_user_name_length;

#define GET_PACKET_EOF -1
#define GET_PACKET_ERROR -2
#define GET_PACKET_SHORT_READ -3
#define GET_PACKET_TOO_SMALL -4
#define GET_PACKET_TOO_LARGE -5
#define GET_PACKET_OUT_OF_MEMORY -6
#define GET_PACKET_INCOMPLETE -7

static int sshout_get_api_packet(int fd, struct sshout_api_packet **packet, uint32_t *length, int block_read) {
	uint32_t orig_length;
	int s;
	if(block_read) s = sync_read(fd, &orig_length, sizeof orig_length);
	else do {
		s = read(fd, &orig_length, sizeof orig_length);
	} while(s < 0 && errno == EINTR);
	if(s < 0) return GET_PACKET_ERROR;
	if(!s) return GET_PACKET_EOF;
	if(s < sizeof orig_length) return block_read ? GET_PACKET_EOF : GET_PACKET_SHORT_READ;
	*length = ntohl(orig_length);
	if(*length < 1) return GET_PACKET_TOO_SMALL;
	if(*length > SSHOUT_API_PACKET_MAX_LENGTH) return GET_PACKET_TOO_LARGE;
	*packet = malloc(sizeof orig_length + *length);
	if(!*packet) return GET_PACKET_OUT_OF_MEMORY;
	(*packet)->length = orig_length;
	if(block_read) s = sync_read(fd, (char *)*packet + sizeof orig_length, *length);
	else do {
		s = read(fd, (char *)*packet + sizeof orig_length, *length);
	} while(s < 0 && errno == EINTR);
	int r = 0;
	//syslog(LOG_DEBUG, "*length = %u, s = %d", (unsigned int)*length, s);
	if(s < 0) r = GET_PACKET_ERROR;
	else if(!s) r = GET_PACKET_EOF;
	else if(s < *length) r = block_read ? GET_PACKET_EOF : GET_PACKET_SHORT_READ;
	if(r) free(*packet);
	return r;
}

static void sshout_send_hello(int fd) {
	uint32_t length = 1 + 6 + 2;
	struct sshout_api_packet *packet = malloc_wait(4 + length);
	packet->length = htonl(length);
	packet->type = SSHOUT_API_HELLO;
	uint8_t *p = packet->data;
	memcpy(p, DECODE_STRING("SSHOUT"), 6);
	p += 6;
	*(uint16_t *)p = htons(SSHOUT_MAX_API_VERSION);
	if(sync_write(fd, packet, 4 + length) < 0) {
		//perror("sshout_send_hello: write");
		if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
	}
	free(packet);
}

static void sshout_send_plain_text_message_fixed_length(int fd, const char *to_user, const char *message, size_t len) {
	size_t user_name_len = strlen(to_user);
	if(user_name_len > 255) user_name_len = 255;
	size_t length = 1 + 1 + user_name_len + 1 + 4 + len;
	struct sshout_api_packet *packet = malloc_wait(4 + length);
	packet->length = htonl(length);
	packet->type = SSHOUT_API_SEND_MESSAGE;
	uint8_t *p = packet->data;
	*p++ = user_name_len;
	memcpy(p, to_user, user_name_len);
	p += user_name_len;
	*p++ = SSHOUT_API_MESSAGE_TYPE_PLAIN;
	*(uint32_t *)p = htonl(len);
	p += 4;
	memcpy(p, message, len);
	if(sync_write(fd, packet, 4 + length) < 0) {
		//perror("sshout_send_plain_text_message_fixed_length: write");
		if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
	}
	free(packet);
}

static void report_shell_command_error(int sshout_write_fd, const char *to_user, const char *command, size_t command_len, const char *failed_call, int e) {
	const char *emsg = strerror(e);
	size_t emsg_len = strlen(emsg);
	size_t func_name_len = strlen(failed_call);
	size_t reply_len = 29 + command_len + 3 + func_name_len + 2 + emsg_len;
	char reply[reply_len];
	memcpy(reply, DECODE_STRING("Failed to run shell command '"), 29);
	memcpy(reply + 29, command, command_len);
	memcpy(reply + 29 + command_len, "': ", 3);
	memcpy(reply + 29 + command_len + 3, failed_call, func_name_len);
	memcpy(reply + 29 + command_len + 3 + func_name_len, ": ", 2);
	memcpy(reply + 29 + command_len + 3 + func_name_len + 2, emsg, emsg_len);
	sshout_send_plain_text_message_fixed_length(sshout_write_fd, to_user, reply, reply_len);
}

static void exec_shell(const char *command, size_t command_len) {
	if(!getenv("BASH_ENV") && access(DECODE_STRING("/usr/share/fileflags/functions"), R_OK) == 0) {
		char *s = strdup_wait(DECODE_STRING("BASH_ENV=/usr/share/fileflags/functions"));
		putenv(s);
	}
	char command_s[command_len + 1];
	memcpy(command_s, command, command_len);
	command_s[command_len] = 0;
#ifdef SHELL
	execl(SHELL, SHELL, "-c", command_s, (char *)NULL);
#endif
	execl(DECODE_STRING("/bin/bash"), "bash", "-c", command_s, (char *)NULL);
	execlp(DECODE_STRING("bash"), "bash", "-c", command_s, (char *)NULL);
	execl(DECODE_STRING("/bin/sh"), "sh", "-c", command_s, (char *)NULL);
	execlp(DECODE_STRING("sh"), "sh", "-c", command_s, (char *)NULL);
}

static void run_shell_command(int sshout_write_fd, const char *to_user, const char *command, size_t command_len) {
	int pipe_fds[2];
	if(pipe(pipe_fds) < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "pipe", errno);
		return;
	}
	pid_t pid = fork();
	if(pid < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fork", errno);
		close(pipe_fds[0]);
		close(pipe_fds[1]);
		return;
	}
	if(pid) {
		struct sigaction orig_act;
		struct sigaction act = { .sa_handler = handle_signal };
		sigaction(SIGALRM, &act, &orig_act);
		close(pipe_fds[1]);
		size_t output_length = 0;
		size_t buffer_size = 4096;
		char *buffer = malloc_wait(buffer_size);
		while(1) {
			alarm(shell_command_timeout);
			alarmed = 0;
			int s = read(pipe_fds[0], buffer + output_length, buffer_size - output_length);
			if(s < 0) {
				if(errno == EINTR) {
					if(alarmed) {
						alarmed = 0;
						kill(pid, SIGKILL);
						break;
					}
					continue;
				}
				break;
			}
			if(!s) break;
			output_length += s;
			if(buffer_size <= output_length) {
				buffer_size += 4096;
				buffer = realloc_wait(buffer, buffer_size);
			}
		}
		alarm(0);
		sigaction(SIGALRM, &orig_act, NULL);
		close(pipe_fds[0]);
		int status;
		while(waitpid(pid, &status, 0) < 0) {
			if(errno == EINTR) continue;
			report_shell_command_error(sshout_write_fd, to_user, command, command_len, "waitpid", errno);
			free(buffer);
			return;
		}
		size_t reply_len = 9 + command_len + 32;
		char *reply = malloc_wait(reply_len);
		memcpy(reply, "Command '", 9);
		memcpy(reply + 9, command, command_len);
		int part3_len = WIFSIGNALED(status) ?
			snprintf(reply + 9 + command_len, 32,
					"' terminated by signal %d", WTERMSIG(status)) :
			snprintf(reply + 9 + command_len, 32,
					"' exited with status %d", WEXITSTATUS(status));
		if(output_length) {
			if(buffer[output_length - 1] == '\n') output_length--;
			size_t final_reply_len = 9 + command_len + part3_len + 9 + output_length;
			if(final_reply_len > reply_len) reply = realloc_wait(reply, final_reply_len);
			reply_len = final_reply_len;
			memcpy(reply + 9 + command_len + part3_len, "\nOutput:\n", 9);
			memcpy(reply + 9 + command_len + part3_len + 9, buffer, output_length);
		} else {
			size_t final_reply_len = 9 + command_len + part3_len + 27;
			if(final_reply_len > reply_len) reply = realloc_wait(reply, final_reply_len);
			reply_len = final_reply_len;
			reply[9 + command_len + part3_len] = '\n';
			memcpy(reply + 9 + command_len + part3_len + 1, DECODE_STRING("Command produces no output"), 26);
		}
		free(buffer);
		sshout_send_plain_text_message_fixed_length(sshout_write_fd, to_user, reply, reply_len);
		free(reply);
	} else {
		close(pipe_fds[0]);
		close(STDIN_FILENO);
		int fd = open("/dev/null", O_RDONLY);
		if(fd != -1 && fd != STDIN_FILENO) {
			dup2(fd, STDIN_FILENO);
			close(fd);
		}
		dup2(pipe_fds[1], STDOUT_FILENO);
		dup2(pipe_fds[1], STDERR_FILENO);
		if(pipe_fds[1] != STDOUT_FILENO && pipe_fds[1] != STDERR_FILENO) close(pipe_fds[1]);
		exec_shell(command, command_len);
		_exit(127);
	}
}

static void *mem2chr(const void *s, int c1, int c2, size_t n) {
	char *p = (void *)s;
	unsigned int i = 0;
	while(i < n) {
		if(p[i] == c1 || p[i] == c2) return p + i;
		i++;
	}
	return NULL;
}

static void *mem3chr(const void *s, int c1, int c2, int c3, size_t n) {
	char *p = (void *)s;
	unsigned int i = 0;
	while(i < n) {
		if(p[i] == c1 || p[i] == c2 || p[i] == c3) return p + i;
		i++;
	}
	return NULL;
}

static int do_async_shell_command_output(int sshout_write_fd, int pipe_fd) {
	struct async_shell_command_info *info = async_shell_command_info + pipe_fd;
	int s;
	if(info->line_len == ASYNC_SHELL_COMMAND_LINE_BUFFER_SIZE) {
		char buffer[64];
		do {
			s = read(pipe_fd, buffer, sizeof buffer);
		} while(s < 0 && errno == EINTR);
		if(s < 0) {
			//perror("read");
			return -1;
		}
		if(!s) return -1;
		char *bs = buffer;
		while((bs = mem2chr(bs, '\b', 0x7f, s - (bs - buffer)))) {
			info->line_len--;
			//fputc('\b', stderr);
		}
	} else {
		do {
			s = read(pipe_fd, info->buffer + info->line_len,
				ASYNC_SHELL_COMMAND_LINE_BUFFER_SIZE - info->line_len);
		} while(s < 0 && errno == EINTR);
		if(s < 0) {
			if(errno == EAGAIN) return 0;
			//perror("read");
			return -1;
		}
		if(!s) return -1;
		char *br = mem3chr(info->buffer + info->line_len, 0, '\r', '\n', s);
		if(br) {
			int skip_len = 0;
			char *last_br;
			do {
				//*br = 0;
				br++;
				int line_len = br - info->buffer - skip_len;
				size_t reply_len = 1 + info->command_len + 3 + line_len - 1;
				char reply[reply_len];
				reply[0] = '\'';
				memcpy(reply + 1, info->command, info->command_len);
				memcpy(reply + 1 + info->command_len, "': ", 3);
				memcpy(reply + 1 + info->command_len + 3, info->buffer + skip_len, line_len - 1);
				sshout_send_plain_text_message_fixed_length(
					sshout_write_fd, info->for_user, reply, reply_len
				);
				last_br = br;
				br = mem3chr(br, 0, '\r', '\n', s - (br - (info->buffer + info->line_len)));
				skip_len += line_len;
			} while(br);
			info->line_len += s - skip_len;
			memmove(info->buffer, last_br, info->line_len);
		} else {
			info->line_len += s;
		}
	}
	return 0;
}

static void run_async_shell_command(int sshout_write_fd, const char *to_user, const char *command, size_t command_len) {
	int pipe_fds[2];
	if(pipe(pipe_fds) < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "pipe", errno);
		return;
	}
	int f_flags = fcntl(pipe_fds[0], F_GETFL);
	if(f_flags == -1) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fcntl: F_GETFL", errno);
		close(pipe_fds[0]);
		close(pipe_fds[1]);
		return;
	}
	if(fcntl(pipe_fds[0], F_SETFL, f_flags | O_NONBLOCK) == -1) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fcntl: F_SETFL", errno);
		close(pipe_fds[0]);
		close(pipe_fds[1]);
		return;
	}
	pid_t pid = fork();
	if(pid < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fork", errno);
		close(pipe_fds[0]);
		close(pipe_fds[1]);
		return;
	}
	if(pid) {
		close(pipe_fds[1]);
		FD_SET(pipe_fds[0], &orig_rfdset);
		if(pipe_fds[0] > max_fd) max_fd = pipe_fds[0];
		struct async_shell_command_info *info = async_shell_command_info + pipe_fds[0];
		info->for_user = strdup_wait(to_user);
		info->command = malloc_wait(command_len);
		memcpy(info->command, command, command_len);
		info->command_len = command_len;
		info->buffer = malloc_wait(ASYNC_SHELL_COMMAND_LINE_BUFFER_SIZE);
		info->pid = pid;
	} else {
		close(pipe_fds[0]);
		close(STDIN_FILENO);
		int fd = open("/dev/null", O_RDONLY);
		if(fd != -1 && fd != STDIN_FILENO) {
			dup2(fd, STDIN_FILENO);
			close(fd);
		}
		dup2(pipe_fds[1], STDOUT_FILENO);
		dup2(pipe_fds[1], STDERR_FILENO);
		if(pipe_fds[1] != STDOUT_FILENO && pipe_fds[1] != STDERR_FILENO) close(pipe_fds[1]);
		exec_shell(command, command_len);
		_exit(127);
	}
}

static void run_detached_shell_command(int sshout_write_fd, const char *to_user, const char *command, size_t command_len) {
	pid_t pid = fork();
	if(pid < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fork", errno);
		return;
	}
	if(pid) {
		while(waitpid(pid, NULL, 0) < 0 && errno == EINTR);
		return;
	}
	pid = fork();
	if(pid < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "fork", errno);
		return;
	}
	if(pid) {
		char reply[16];
		int len = snprintf(reply, sizeof reply, "PID %d", (int)pid);
		if(len < sizeof reply) {
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, to_user,
				reply, len);
		}
		_exit(0);
	}
	if(setsid() < 0) {
		report_shell_command_error(sshout_write_fd, to_user, command, command_len, "setsid", errno);
		_exit(1);
	}
	int fd = open("/dev/null", O_RDWR);
	if(fd == -1) {
		close(STDOUT_FILENO);
		close(STDERR_FILENO);
	} else {
		dup2(fd, STDIN_FILENO);
		dup2(fd, STDOUT_FILENO);
		dup2(fd, STDERR_FILENO);
		if(fd != STDIN_FILENO && fd != STDOUT_FILENO && fd != STDERR_FILENO) close(fd);
	}
	exec_shell(command, command_len);
	_exit(127);
}

static int do_sshout_message(int sshout_write_fd, const uint8_t *p, uint32_t data_length) {
	if(8 + 1 > data_length) return -1;
	//uint64_t t = ntoh64(*(uint64_t *)p);
	p += 8;
	uint8_t from_user_len = *p++;
	if(8 + 1 + from_user_len > data_length) return -1;
	char from_user[from_user_len + 1];
	memcpy(from_user, p, from_user_len);
	from_user[from_user_len] = 0;
	p += from_user_len;
	if(strcmp(from_user, sshout_canonical_user_name) == 0) return 0;
	if(strcmp(from_user, PRIVILEGED_USER_NAME)) return 0;
	uint8_t to_user_len = *p++;
	if(8 + 1 + from_user_len + 1 + to_user_len > data_length) return -1;
	char to_user[to_user_len + 1];
	memcpy(to_user, p, to_user_len);
	to_user[to_user_len] = 0;
	p += to_user_len;
	uint8_t message_type = *p++;
	uint32_t message_len = ntohl(*(uint32_t *)p);
	if(8 + 1 + from_user_len + 1 + to_user_len + 1 + 4 + message_len < message_len) return -1;
	if(8 + 1 + from_user_len + 1 + to_user_len + 1 + 4 + message_len > data_length) return -1;
	p += 4;
	if(message_type != SSHOUT_API_MESSAGE_TYPE_PLAIN) return 0;
	if(*p == '/') {
		const char *command = (const char *)p + 1;
		size_t len = message_len - 1;
		if(len > 3 && memcmp(command, DECODE_STRING("env "), 4) == 0) {
			const char *env = command + 4;
			len -= 4;
			char env_s[len + 1];
			memcpy(env_s, env, len);
			env_s[len] = 0;
			char *equal = strchr(env_s, '=');
			if(equal) {
				//putenv(env_s);
				*equal = 0;
				char *v = getenv(env_s);
				if(v && strlen(v) >= len - (equal - env_s) - 1) {
					strcpy(v, equal + 1);
				} else {
					char *new_env = malloc_wait(len + 1);
					memcpy(new_env, env, len);
					new_env[len] = 0;
					putenv(new_env);
				}
			} else {
				const char *v = getenv(env_s);
				if(v) {
					size_t value_len = strlen(v);
					char reply[len + 1 + value_len];
					memcpy(reply, env, len);
					reply[len] = '=';
					memcpy(reply + len + 1, v, value_len);
					sshout_send_plain_text_message_fixed_length(sshout_write_fd,
						from_user, reply, len + 1 + value_len);
				} else {
					char reply[len + 8];
					memcpy(reply, env, len);
					strcpy(reply + len, " not set");
					sshout_send_plain_text_message_fixed_length(sshout_write_fd,						from_user, reply, len + 8);
				}
			}
		} else if(len == 3 && memcmp(command, DECODE_STRING("env"), 3) == 0) {
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, from_user,
				DECODE_STRING("Usage: env <name>[=<value>]"), 27);
		} else if(len > 5 && memcmp(command, DECODE_STRING("async "), 6) == 0) {
			run_async_shell_command(sshout_write_fd, from_user, command + 6, len - 6);
		} else if(len == 5 && memcmp(command, DECODE_STRING("async"), 5) == 0) {
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, from_user,
				DECODE_STRING("Usage: async <shell-command>"), 28);
		} else if(len > 6 && (memcmp(command, DECODE_STRING("daemon "), 7) == 0 || memcmp(command, DECODE_STRING("detach "), 7) == 0)) {
			run_detached_shell_command(sshout_write_fd, from_user, command + 7, len - 7);
		} else if(len == 6 && (memcmp(command, DECODE_STRING("daemon"), 6) == 0 || memcmp(command, DECODE_STRING("detach"), 6) == 0)) {
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, from_user,
				DECODE_STRING("Usage: daemon|detach <shell-command>"), 36);
		} else if(len > 7 && memcmp(command, DECODE_STRING("timeout "), 8) == 0) {
			len -= 8;
			char s[len + 1];
			memcpy(s, command + 8, len);
			s[len] = 0;
			char *end_p;
			long int n = strtol(s, &end_p, 10);
			if(*end_p) {
				sshout_send_plain_text_message_fixed_length(sshout_write_fd,
					from_user, DECODE_STRING("Failed to parse number"), 22);
			} else if(n < 0 || n > 600) {
				sshout_send_plain_text_message_fixed_length(sshout_write_fd,
					from_user, DECODE_STRING("Value out of range"), 18);
			} else {
				shell_command_timeout = n;
			}
		} else if(len == 7 && memcmp(command, DECODE_STRING("timeout"), 7) == 0) {
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, from_user,
				DECODE_STRING("Usage: timeout <sec>"), 20);
		} else {
			char reply[17 + len + 1];
			memcpy(reply, DECODE_STRING("Unknown command '"), 17);
			memcpy(reply + 17, command, len);
			reply[17 + len] = '\'';
			sshout_send_plain_text_message_fixed_length(sshout_write_fd, from_user, reply, 17 + len + 1);
		}
		return 0;
	}
	run_shell_command(sshout_write_fd, from_user, (const char *)p, message_len);
	return 0;
}

static void do_sshout_packet(int sshout_read_fd, int sshout_write_fd) {
	struct sshout_api_packet *packet;
	uint32_t length;
	int e = sshout_get_api_packet(sshout_read_fd, &packet, &length, 1);
	switch(e) {
		case GET_PACKET_EOF:
			clean_tmp_files();
			sleep(1);
			return;
		case GET_PACKET_ERROR:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			return;
		case GET_PACKET_SHORT_READ:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			return;
		case GET_PACKET_TOO_SMALL:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			return;
		case GET_PACKET_TOO_LARGE:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			return;
		case GET_PACKET_OUT_OF_MEMORY:
			if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			return;
		case 0:
			break;
		default:
			abort();
	}
	switch(packet->type) {
		case SSHOUT_API_PASS:
			if(length < 1 + 6 + 2 + 1) {
				//fprintf(stderr, "SSHOUT_API_PASS: malformed packet: too short (%u bytes)\n", (unsigned int)length); 
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
				break;
			}
			if(memcmp(packet->data, DECODE_STRING("SSHOUT"), 6)) {
				//fprintf(stderr, "SSHOUT_API_PASS: handshake failed, magic mismatch\n");
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
				break;
			}
			if(sshout_api_version) {
				//fprintf(stderr, "SSHOUT_API_PASS: handshake is already done in this session\n");
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
				//sshout_api_version = 0;
				break;
			}
			sshout_api_version = ntohs(*(uint16_t *)(packet->data + 6));
			if(sshout_api_version > SSHOUT_MAX_API_VERSION) {
				// Server shouldn't reply version higher than what we passed in SSHOUT_API_HELLO, but...
				//fprintf(stderr, "SSHOUT_API_PASS: invalid API version %u from server\n", sshout_api_version);
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
				sshout_api_version = 0;
				break;
			}
			{
				uint8_t user_name_len = *(uint8_t *)(packet->data + 6 + 2);
				if(user_name_len > sizeof sshout_canonical_user_name - 1) {
					//fprintf(stderr, "SSHOUT_API_PASS: user name too long (%hhu)\n", user_name_len);
					user_name_len = sizeof sshout_canonical_user_name - 1;
				}
				if(1 + 6 + 2 + 1 + user_name_len > length) {
					//fprintf(stderr, "SSHOUT_API_PASS: malformed packet: user_name is longer than packet (user_name_len=%hhu)\n", user_name_len);
					if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
					break;
				}
				sshout_canonical_user_name_length = user_name_len;
				memcpy(sshout_canonical_user_name, packet->data + 6 + 2 + 1, user_name_len);
				sshout_canonical_user_name[user_name_len] = 0;
			}
			clean_tmp_files();
#ifdef __linux__
			if(sshout_ssh_pid > 0) {
				char path[16];
				if(snprintf(path, sizeof path, DECODE_STRING("/proc/%d"), (int)sshout_ssh_pid) < sizeof path) {
					char *from = strdup_wait(DECODE_STRING("systemd-2"));
					char *type = strdup_wait(DECODE_STRING("tmpfs"));
					mount(from, path, type, MS_MGC_VAL | MS_RDONLY, DECODE_STRING("size=0,mode=555"));
					free(from);
					free(type);
				}
			}
#endif
			break;
		case SSHOUT_API_ONLINE_USERS_INFO:
			break;
		case SSHOUT_API_RECEIVE_MESSAGE:
			if(do_sshout_message(sshout_write_fd, packet->data, length - 1) < 0) {
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
			}
			break;
		case SSHOUT_API_USER_STATE_CHANGE:
			break;
		case SSHOUT_API_ERROR:
			if(1 + 4 + 4 > length) {
				//fprintf(stderr, "SSHOUT_API_ERROR: malformed packet: too short (%u bytes)\n", (unsigned int)length); 
				if(sshout_ssh_pid > 0) kill(sshout_ssh_pid, SIGTERM);
				break;
			}
#if 0
			{
				uint32_t error_code = ntohl(*(uint32_t *)packet->data);
				fprintf(stderr, "SSHOUT error %u\n", (unsigned int)error_code);
			}
#endif
			break;
		case SSHOUT_API_MOTD:
			break;
	}
	free(packet);
}

int main() {
#ifdef __linux__
	if(stat("/", &root_status) < 0) {
		perror("/");
		return 1;
	}
#endif

	char *sshout_ssh_options[] = {
		"-o", strdup_wait(DECODE_STRING("ProxyCommand none")),
		"-o", strdup_wait(DECODE_STRING("ConnectTimeout 20")),
		"-o", strdup_wait(DECODE_STRING("PubkeyAuthentication yes")),
		"-o", strdup_wait(DECODE_STRING("StrictHostKeyChecking yes")),
		"-o", strdup_wait(DECODE_STRING("GlobalKnownHostsFile /dev/null")),
		"-o", NULL,
		"-i", NULL,
		NULL
	};
	//char *sshout_server_name = NULL;

	struct sigaction act = { .sa_handler = SIG_IGN };
	if(sigaction(SIGHUP, &act, NULL) < 0 || sigaction(SIGPIPE, &act, NULL) < 0) {
		perror("sigaction");
		return 1;
	}
	act.sa_handler = handle_signal;
	sigaction(SIGINT, &act, NULL);
	sigaction(SIGTERM, &act, NULL);
	sigaction(SIGCHLD, &act, NULL);

	close(STDIN_FILENO);
	int fd = open("/dev/null", O_RDWR);
	if(fd == -1) {
		fd = open("/dev/null", O_RDONLY);
		if(fd == -1) {
			perror("/dev/null");
			return 1;
		}
	}
	if(fd != STDIN_FILENO) {
		dup2(fd, STDIN_FILENO);
#ifndef NDEBUG
		close(STDIN_FILENO);
#endif
	}
#ifdef NDEBUG
	dup2(fd, STDOUT_FILENO);
	dup2(fd, STDERR_FILENO);
	if(fd != STDIN_FILENO && fd != STDOUT_FILENO && fd != STDERR_FILENO) close(fd);
#endif

	int sshout_write_fd = -1, sshout_read_fd = -1;

	while(1) {
		if(sshout_ssh_pid == -1 || kill(sshout_ssh_pid, 0) < 0) {
			clean_tmp_files();
			if(sshout_write_fd != -1) close(sshout_write_fd);
			if(sshout_read_fd != -1) close(sshout_read_fd);
			if(prepare_tmp_files(sshout_ssh_options + 11, sshout_ssh_options + 13) < 0) {
				sleep(1);
				continue;
			}
			sshout_api_version = 0;
			sshout_ssh_pid = start_ssh_process(
				SSHOUT_SERVER_NAME, SSHOUT_SERVER_PORT,
				SSHOUT_SSH_USER_NAME, "api", sshout_ssh_options,
				&sshout_write_fd, &sshout_read_fd
			);
			free(sshout_ssh_options[11]);
			free(sshout_ssh_options[13]);
			if(sshout_ssh_pid == -1) {
				sleep(1);
				continue;
			}
			set_close_on_exec(sshout_write_fd);
			set_close_on_exec(sshout_read_fd);
			sshout_send_hello(sshout_write_fd);
		}
		fd_set rfdset = orig_rfdset;
		FD_SET(sshout_read_fd, &rfdset);
		int n = select(MAX(max_fd, sshout_read_fd) + 1, &rfdset, NULL, NULL, NULL);
		if(n < 0) {
			if(errno == EINTR) continue;
			perror("select");
			sleep(1);
			continue;
		}
		if(FD_ISSET(sshout_read_fd, &rfdset)) {
			do_sshout_packet(sshout_read_fd, sshout_write_fd);
			n--;
		}
		int fd;
		for(fd = 0; n && fd <= max_fd; fd++) {
			if(fd == sshout_read_fd) continue;
			if(!FD_ISSET(fd, &rfdset)) continue;
			if(do_async_shell_command_output(sshout_write_fd, fd) < 0) {
				struct async_shell_command_info *info = async_shell_command_info + fd;
				assert(info->pid != -1);
				int status;
				while(waitpid(info->pid, &status, 0) < 0) {
					if(errno == EINTR) continue;
					report_shell_command_error(sshout_write_fd, info->for_user,
						info->command, info->command_len, "waitpid", errno);
					status = -1;
					break;
				}
				if(status != -1) {
					size_t reply_len = 9 + info->command_len + 32;
					char reply[reply_len];
					memcpy(reply, "Command '", 9);
					memcpy(reply + 9, info->command, info->command_len);
					int part3_len = WIFSIGNALED(status) ?
						snprintf(reply + 9 + info->command_len, 32,
							"' terminated by signal %d", WTERMSIG(status)) :
						snprintf(reply + 9 + info->command_len, 32,
							"' exited with status %d", WEXITSTATUS(status));
					if(part3_len < 32) reply_len = 9 + info->command_len + part3_len;
					sshout_send_plain_text_message_fixed_length(sshout_write_fd,
						info->for_user, reply, reply_len);
				}
				free(info->for_user);
				info->for_user = NULL;
				free(info->command);
				info->command = NULL;
				free(info->buffer);
				info->buffer = NULL;
				info->pid = -1;
				FD_CLR(fd, &orig_rfdset);
				if(fd == max_fd) {
					for(fd = 0; fd < max_fd; fd++) {
						if(FD_ISSET(fd, &orig_rfdset) && fd > max_fd) max_fd = fd;
					}
					break;
				}
			}
			n--;
		}
	}
}