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path: root/networking/telnetd.c
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/* vi: set sw=4 ts=4: */
/*
 * Simple telnet server
 * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
 * Copyright (c) 2014 RIPE NCC <atlas@ripe.net>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 *
 * ---------------------------------------------------------------------------
 * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
 ****************************************************************************
 *
 * The telnetd manpage says it all:
 *
 *   Telnetd operates by allocating a pseudo-terminal device (see pty(4))  for
 *   a client, then creating a login process which has the slave side of the
 *   pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the
 *   master side of the pseudo-terminal, implementing the telnet protocol and
 *   passing characters between the remote client and the login process.
 *
 * Vladimir Oleynik <dzo@simtreas.ru> 2001
 *     Set process group corrections, initial busybox port
 */

#define DEBUG 0

#include "libbb.h"
#include <syslog.h>

#if DEBUG
#define TELCMDS
#define TELOPTS
#endif
#include <arpa/telnet.h>

#define ATLAS 1

#ifdef ATLAS
#include <string.h>
#include <unistd.h>
#include <linux/reboot.h>

#define LOGIN_PREFIX	"Atlas probe, see http://atlas.ripe.net/\r\n\r\n"
#define LOGIN_PROMPT	" login: "
#define PASSWORD_PROMPT	"\r\nPassword: "

#define ATLAS_LOGIN	"C_TO_P_TEST_V1"
#define ATLAS_SESSION_FILE	"/home/atlas/status/con_session_id.txt"
#define SESSION_ID_PREFIX	"SESSION_ID "

#define CMD_CRONTAB	"CRONTAB "
#define CMD_CRONLINE	"CRONLINE "
#define CMD_ONEOFF	"ONEOFF "
#define CMD_REBOOT	"REBOOT"

#define CRLF		"\r\n"
#define RESULT_OK	"OK" CRLF CRLF
#define BAD_PASSWORD	"BAD_PASSWORD" CRLF CRLF
#define BAD_COMMAND	"BAD_COMMAND" CRLF CRLF
#define NAME_TOO_LONG	"NAME_TOO_LONG" CRLF CRLF
#define CRONTAB_BUSY	"CRONTAB_BUSY" CRLF CRLF
#define CREATE_FAILED	"UNABLE_TO_CREATE_NEW_CRONTAB" CRLF CRLF
#define IO_ERROR	"IO_ERROR" CRLF CRLF
#define BAD_PATH	"BAD_PATH" CRLF CRLF

#define CRONUSER	"root"
#define CRONTAB_NEW_SUF	"/" CRONUSER ".new"
#define CRONTAB_SUFFIX	"/" CRONUSER
#define CRONUPDATE	"/cron.update"
#define UPDATELINE	CRONUSER "\n"
#define ONEOFF_SUFFIX	".new"
#define SAFE_PREFIX	ATLAS_CRONS

enum state
{
	DO_TRADITIONAL,
	GET_LOGINNAME,
	GET_PASSWORD,
	GET_CMD,
	DO_CRONTAB,
	EOM_SEEN
};
#endif

/* Structure that describes a session */
struct tsession {
	struct tsession *next;
	int sockfd_read, sockfd_write, ptyfd;
	int shell_pid;

#ifdef ATLAS
	enum state state;
#endif

	/* two circular buffers */
	/*char *buf1, *buf2;*/
/*#define TS_BUF1 ts->buf1*/
/*#define TS_BUF2 TS_BUF2*/
#define TS_BUF1 ((unsigned char*)(ts + 1))
#define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
	int rdidx1, wridx1, size1;
	int rdidx2, wridx2, size2;
};

/* Two buffers are directly after tsession in malloced memory.
 * Make whole thing fit in 8k */
enum { BUFSIZE = (8 * 1024 - sizeof(struct tsession)) / 2 };

#ifdef ATLAS
static int equal_sessionid(char *passwd);
static void add_2sock(struct tsession *ts, const char *str);
static void pack_4sock(void);
static char *getline_2pty(struct tsession *ts);
static void pack_2pty(struct tsession *ts);
static int start_crontab(struct tsession *ts, char *line);
static void add_to_crontab(struct tsession *ts, char *line);
static void end_crontab(struct tsession *ts);
static void do_oneoff(struct tsession *ts, char *line);
int validate_filename(const char *path, const char *prefix);
#endif

/* Globals */
static int maxfd;
static struct tsession *sessions;
static const char *loginpath = "/bin/login";
static const char *issuefile = "/etc/issue.net";

#ifdef ATLAS
/* Place to store the file handle and directory name for a new crontab */
static FILE *atlas_crontab;
static char atlas_dirname[256];
static struct tsession *atlas_ts;	/* Allow only one 'atlas' connection
					 * at a time. The old one
					 * self-destructs when a new one is
					 * started.
					 */
#endif

/*
   Remove all IAC's from buf1 (received IACs are ignored and must be removed
   so as to not be interpreted by the terminal).  Make an uninterrupted
   string of characters fit for the terminal.  Do this by packing
   all characters meant for the terminal sequentially towards the end of buf.

   Return a pointer to the beginning of the characters meant for the terminal.
   and make *num_totty the number of characters that should be sent to
   the terminal.

   Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
   past (bf + len) then that IAC will be left unprocessed and *processed
   will be less than len.

   FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
   what is the escape character?  We aren't handling that situation here.

   CR-LF ->'s CR mapping is also done here, for convenience.

   NB: may fail to remove iacs which wrap around buffer!
 */
static unsigned char *
remove_iacs(struct tsession *ts, int *pnum_totty)
{
	unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
	unsigned char *ptr = ptr0;
	unsigned char *totty = ptr;
	unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
	int num_totty;

	while (ptr < end) {
		if (*ptr != IAC) {
			char c = *ptr;

			*totty++ = c;
			ptr++;
			/* We map \r\n ==> \r for pragmatic reasons.
			 * Many client implementations send \r\n when
			 * the user hits the CarriageReturn key.
			 */
			if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
				ptr++;
			continue;
		}

		if ((ptr+1) >= end)
			break;
		if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */
			ptr += 2;
			continue;
		}
		if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */
			*totty++ = ptr[1];
			ptr += 2;
			continue;
		}

		/*
		 * TELOPT_NAWS support!
		 */
		if ((ptr+2) >= end) {
			/* only the beginning of the IAC is in the
			buffer we were asked to process, we can't
			process this char. */
			break;
		}
		/*
		 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
		 */
		if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
			struct winsize ws;
			if ((ptr+8) >= end)
				break;	/* incomplete, can't process */
			ws.ws_col = (ptr[3] << 8) | ptr[4];
			ws.ws_row = (ptr[5] << 8) | ptr[6];
			ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
			ptr += 9;
			continue;
		}
		/* skip 3-byte IAC non-SB cmd */
#if DEBUG
		fprintf(stderr, "Ignoring IAC %s,%s\n",
				TELCMD(ptr[1]), TELOPT(ptr[2]));
#endif
		ptr += 3;
	}

	num_totty = totty - ptr0;
	*pnum_totty = num_totty;
	/* the difference between ptr and totty is number of iacs
	   we removed from the stream. Adjust buf1 accordingly. */
	if ((ptr - totty) == 0) /* 99.999% of cases */
		return ptr0;
	ts->wridx1 += ptr - totty;
	ts->size1 -= ptr - totty;
	/* move chars meant for the terminal towards the end of the buffer */
	return memmove(ptr - num_totty, ptr0, num_totty);
}


static struct tsession *
make_new_session(
		USE_FEATURE_TELNETD_STANDALONE(int sock)
		SKIP_FEATURE_TELNETD_STANDALONE(void)
) {
#ifndef ATLAS
	const char *login_argv[2];
	struct termios termbuf;
	int fd, pid;
	char tty_name[GETPTY_BUFSIZE];
#endif
	struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);

#ifdef ATLAS
	ts->state= GET_LOGINNAME;
#endif

	/*ts->buf1 = (char *)(ts + 1);*/
	/*ts->buf2 = ts->buf1 + BUFSIZE;*/

#ifdef ATLAS
	ts->ptyfd= 0;
#else
	/* Got a new connection, set up a tty. */
	fd = xgetpty(tty_name);
	if (fd > maxfd)
		maxfd = fd;
	ts->ptyfd = fd;
	ndelay_on(fd);
#endif /* ATLAS */

#if ENABLE_FEATURE_TELNETD_STANDALONE
	ts->sockfd_read = sock;
	/* SO_KEEPALIVE by popular demand */
	setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
	ndelay_on(sock);
	if (!sock) { /* We are called with fd 0 - we are in inetd mode */
		sock++; /* so use fd 1 for output */
		ndelay_on(sock);
	}
	ts->sockfd_write = sock;
	if (sock > maxfd)
		maxfd = sock;
#else
	/* SO_KEEPALIVE by popular demand */
	setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
	/* ts->sockfd_read = 0; - done by xzalloc */
	ts->sockfd_write = 1;
	ndelay_on(0);
	ndelay_on(1);
#endif
	/* Make the telnet client understand we will echo characters so it
	 * should not do it locally. We don't tell the client to run linemode,
	 * because we want to handle line editing and tab completion and other
	 * stuff that requires char-by-char support. */
	{
		static const char iacs_to_send[] ALIGN1 = {
			IAC, DO, TELOPT_ECHO,
			IAC, DO, TELOPT_NAWS,
			IAC, DO, TELOPT_LFLOW,
			IAC, WILL, TELOPT_ECHO,
			IAC, WILL, TELOPT_SGA
		};
		memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
		ts->rdidx2 = sizeof(iacs_to_send);
		ts->size2 = sizeof(iacs_to_send);
	}

#ifdef ATLAS	/* Split original function into two */
	return ts;
}

static int start_login(struct tsession *ts, char *user)
{
	int fd, pid;
	const char *login_argv[3];
	struct termios termbuf;
	char tty_name[GETPTY_BUFSIZE];

	/* Got a new connection, set up a tty. */
	fd = xgetpty(tty_name);
	if (fd > maxfd)
		maxfd = fd;
	ts->ptyfd = fd;
	ndelay_on(fd);
#endif /* ATLAS */

	fflush(NULL); /* flush all streams */
	pid = vfork(); /* NOMMU-friendly */
	if (pid < 0) {
		free(ts);
		close(fd);
		/* sock will be closed by caller */
		bb_perror_msg("vfork");
#ifdef ATLAS
		return -1;
#else
		return NULL;
#endif
	}
	if (pid > 0) {
		/* Parent */
		ts->shell_pid = pid;
#ifdef ATLAS
		return 0;
#else
		return ts;
#endif
	}

	/* Child */
	/* Careful - we are after vfork! */

	/* make new session and process group */
	setsid();

	/* Restore default signal handling */
	bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);

	/* open the child's side of the tty. */
	/* NB: setsid() disconnects from any previous ctty's. Therefore
	 * we must open child's side of the tty AFTER setsid! */
	close(0);
	xopen(tty_name, O_RDWR); /* becomes our ctty */
	xdup2(0, 1);
	xdup2(0, 2);
	tcsetpgrp(0, getpid()); /* switch this tty's process group to us */

	/* The pseudo-terminal allocated to the client is configured to operate in
	 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
	tcgetattr(0, &termbuf);
	termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
	termbuf.c_oflag |= ONLCR | XTABS;
	termbuf.c_iflag |= ICRNL;
	termbuf.c_iflag &= ~IXOFF;
	/*termbuf.c_lflag &= ~ICANON;*/
	tcsetattr_stdin_TCSANOW(&termbuf);

	/* Uses FILE-based I/O to stdout, but does fflush(stdout),
	 * so should be safe with vfork.
	 * I fear, though, that some users will have ridiculously big
	 * issue files, and they may block writing to fd 1,
	 * (parent is supposed to read it, but parent waits
	 * for vforked child to exec!) */
	print_login_issue(issuefile, tty_name);

	/* Exec shell / login / whatever */
	login_argv[0] = loginpath;
#ifdef ATLAS
	login_argv[1] = user;
	login_argv[2] = NULL;
#else
	login_argv[1] = NULL;
#endif
	/* exec busybox applet (if PREFER_APPLETS=y), if that fails,
	 * exec external program */
	BB_EXECVP(loginpath, (char **)login_argv);
	/* _exit is safer with vfork, and we shouldn't send message
	 * to remote clients anyway */
	_exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", loginpath);*/
}

/* Must match getopt32 string */
enum {
		/*	 (1 << 0)	-f */
		/*	 (1 << 1)	-l */
	OPT_WATCHCHILD = (1 << 2), /* -K */
	OPT_INETD      = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
		/*	 (1 << 4)	-P */
	OPT_PORT       = (1 << 5) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
		/*	 (1 << 6)	-b */
	OPT_FOREGROUND = (1 << 7) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
};

#if ENABLE_FEATURE_TELNETD_STANDALONE

static void
free_session(struct tsession *ts)
{
	struct tsession *t = sessions;

	if (option_mask32 & OPT_INETD)
		exit(EXIT_SUCCESS);

	/* Unlink this telnet session from the session list */
	if (t == ts)
		sessions = ts->next;
	else {
		while (t->next != ts)
			t = t->next;
		t->next = ts->next;
	}

#if 0
	/* It was said that "normal" telnetd just closes ptyfd,
	 * doesn't send SIGKILL. When we close ptyfd,
	 * kernel sends SIGHUP to processes having slave side opened. */
	kill(ts->shell_pid, SIGKILL);
	wait4(ts->shell_pid, NULL, 0, NULL);
#endif
#ifdef ATLAS
	if (ts->ptyfd != 0)
		close(ts->ptyfd);
#else
	close(ts->ptyfd);
#endif
	close(ts->sockfd_read);
	/* We do not need to close(ts->sockfd_write), it's the same
	 * as sockfd_read unless we are in inetd mode. But in inetd mode
	 * we do not reach this */
	free(ts);

	/* Scan all sessions and find new maxfd */
	maxfd = 0;
	ts = sessions;
	while (ts) {
		if (maxfd < ts->ptyfd)
			maxfd = ts->ptyfd;
		if (maxfd < ts->sockfd_read)
			maxfd = ts->sockfd_read;
#if 0
		/* Again, sockfd_write == sockfd_read here */
		if (maxfd < ts->sockfd_write)
			maxfd = ts->sockfd_write;
#endif
		ts = ts->next;
	}
}

#else /* !FEATURE_TELNETD_STANDALONE */

/* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
#define free_session(ts) return 0

#endif

static void handle_sigchld(int sig UNUSED_PARAM)
{
	pid_t pid;
	struct tsession *ts;

	/* Looping: more than one child may have exited */
	while (1) {
		pid = wait_any_nohang(NULL);
		if (pid <= 0)
			break;
		ts = sessions;
		while (ts) {
			if (ts->shell_pid == pid) {
				ts->shell_pid = -1;
				break;
			}
			ts = ts->next;
		}
	}
}

static void kick_watchdog(void)
{
	int fdwatchdog = open("/dev/watchdog", O_RDWR);
	if (fdwatchdog != -1)
	{
		write(fdwatchdog, "1", 1);
		close(fdwatchdog);
	}
}

int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int telnetd_main(int argc UNUSED_PARAM, char **argv)
{
	fd_set rdfdset, wrfdset;
	unsigned opt;
	int count, probe_id;
	int num_totty;
	struct tsession *ts;
	char *line;
#if ENABLE_FEATURE_TELNETD_STANDALONE
#define IS_INETD (opt & OPT_INETD)
	int master_fd = master_fd; /* be happy, gcc */
	unsigned portnbr = 23;
	char *opt_bindaddr = NULL;
	char *opt_portnbr;
	const char *PidFileName = NULL;
	char buf[80];
#else
	enum {
		IS_INETD = 1,
		master_fd = -1,
		portnbr = 23,
	};
#endif
	struct timeval tv;

	/* Even if !STANDALONE, we accept (and ignore) -i, thus people
	 * don't need to guess whether it's ok to pass -i to us */
	opt = getopt32(argv, "f:l:KiP:" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
			&issuefile, &loginpath, &PidFileName
			USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
	if (!IS_INETD /*&& !re_execed*/) {
		/* inform that we start in standalone mode?
		 * May be useful when people forget to give -i */
		/*bb_error_msg("listening for connections");*/
		if (!(opt & OPT_FOREGROUND)) {
			/* DAEMON_CHDIR_ROOT was giving inconsistent
			 * behavior with/without -F, -i */
			bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
		}
	}
	/* Redirect log to syslog early, if needed */
	if (IS_INETD || !(opt & OPT_FOREGROUND)) {
		openlog(applet_name, 0, LOG_USER);
		logmode = LOGMODE_SYSLOG;
	}
	USE_FEATURE_TELNETD_STANDALONE(
		if (opt & OPT_PORT)
			portnbr = xatou16(opt_portnbr);
	);

	if(PidFileName)
	{
		write_pidfile(PidFileName);
	}

	/* Used to check access(loginpath, X_OK) here. Pointless.
	 * exec will do this for us for free later. */

#if ENABLE_FEATURE_TELNETD_STANDALONE
	if (IS_INETD) {
		sessions = make_new_session(0);
		if (!sessions) /* pty opening or vfork problem, exit */
			return 1; /* make_new_session prints error message */
	} else {
		master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
		xlisten(master_fd, 1);
	}
#else
	sessions = make_new_session();
	if (!sessions) /* pty opening or vfork problem, exit */
		return 1; /* make_new_session prints error message */
#endif

	/* We don't want to die if just one session is broken */
	signal(SIGPIPE, SIG_IGN);

	if (opt & OPT_WATCHCHILD)
		signal(SIGCHLD, handle_sigchld);
	else /* prevent dead children from becoming zombies */
		signal(SIGCHLD, SIG_IGN);

/*
   This is how the buffers are used. The arrows indicate the movement
   of data.
   +-------+     wridx1++     +------+     rdidx1++     +----------+
   |       | <--------------  | buf1 | <--------------  |          |
   |       |     size1--      +------+     size1++      |          |
   |  pty  |                                            |  socket  |
   |       |     rdidx2++     +------+     wridx2++     |          |
   |       |  --------------> | buf2 |  --------------> |          |
   +-------+     size2++      +------+     size2--      +----------+

   size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
   size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"

   Each session has got two buffers. Buffers are circular. If sizeN == 0,
   buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
   rdidxN == wridxN.
*/
 again:
	FD_ZERO(&rdfdset);
	FD_ZERO(&wrfdset);

	kick_watchdog();

	/* Select on the master socket, all telnet sockets and their
	 * ptys if there is room in their session buffers.
	 * NB: scalability problem: we recalculate entire bitmap
	 * before each select. Can be a problem with 500+ connections. */
	ts = sessions;
	while (ts) {
		struct tsession *next = ts->next; /* in case we free ts. */
		if (ts->shell_pid == -1) {
			/* Child died and we detected that */
			free_session(ts);
		} else {
#ifdef ATLAS
			if (ts->size1 > 0 && ts->state == DO_TRADITIONAL)
				/* can write to pty */
#else
			if (ts->size1 > 0)       /* can write to pty */
#endif
				FD_SET(ts->ptyfd, &wrfdset);
			if (ts->size1 < BUFSIZE) /* can read from socket */
				FD_SET(ts->sockfd_read, &rdfdset);
			if (ts->size2 > 0)       /* can write to socket */
				FD_SET(ts->sockfd_write, &wrfdset);
#ifdef ATLAS
			if (ts->size2 < BUFSIZE &&
				ts->state == DO_TRADITIONAL)
				/* can read from pty */
#else
			if (ts->size2 < BUFSIZE) /* can read from pty */
#endif
				FD_SET(ts->ptyfd, &rdfdset);
		}
		ts = next;
	}
	if (!IS_INETD) {
		FD_SET(master_fd, &rdfdset);
		/* This is needed because free_session() does not
		 * take master_fd into account when it finds new
		 * maxfd among remaining fd's */
		if (master_fd > maxfd)
			maxfd = master_fd;
	}

	tv.tv_sec= 10;
	tv.tv_usec= 0;
	count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, &tv);
	if (count < 0)
		goto again; /* EINTR or ENOMEM */

#if ENABLE_FEATURE_TELNETD_STANDALONE
	/* First check for and accept new sessions. */
	if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
		int fd;
		struct tsession *new_ts;

		fd = accept(master_fd, NULL, NULL);
		if (fd < 0)
			goto again;
		/* Create a new session and link it into our active list */
		new_ts = make_new_session(fd);
		if (new_ts) {
#ifdef ATLAS
			char *hostname;

			hostname= safe_gethostname();
			probe_id= get_probe_id();
			add_2sock(new_ts, LOGIN_PREFIX);
			snprintf(buf, sizeof(buf), "Probe %d (%s)",
				probe_id, hostname);
			add_2sock(new_ts, buf);
			add_2sock(new_ts, LOGIN_PROMPT);
			free(hostname);
#endif /* ATLAS */
			new_ts->next = sessions;
			sessions = new_ts;
		} else {
			close(fd);
		}
	}
#endif

	/* Then check for data tunneling. */
	ts = sessions;
	while (ts) { /* For all sessions... */
		struct tsession *next = ts->next; /* in case we free ts. */

		if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
			unsigned char *ptr;
			/* Write to pty from buffer 1. */
			ptr = remove_iacs(ts, &num_totty);
			count = safe_write(ts->ptyfd, ptr, num_totty);
			if (count < 0) {
				if (errno == EAGAIN)
					goto skip1;
				goto kill_session;
			}
			ts->size1 -= count;
			ts->wridx1 += count;
			if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
				ts->wridx1 = 0;
		}
 skip1:
		if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
			/* Write to socket from buffer 2. */
			count = MIN(BUFSIZE - ts->wridx2, ts->size2);
			count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
			if (count < 0) {
				if (errno == EAGAIN)
					goto skip2;
				goto kill_session;
			}
			ts->size2 -= count;
			ts->wridx2 += count;
			if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
				ts->wridx2 = 0;
		}
 skip2:
		/* Should not be needed, but... remove_iacs is actually buggy
		 * (it cannot process iacs which wrap around buffer's end)!
		 * Since properly fixing it requires writing bigger code,
		 * we rely instead on this code making it virtually impossible
		 * to have wrapped iac (people don't type at 2k/second).
		 * It also allows for bigger reads in common case. */
		if (ts->size1 == 0) {
			ts->rdidx1 = 0;
			ts->wridx1 = 0;
		}
		if (ts->size2 == 0) {
			ts->rdidx2 = 0;
			ts->wridx2 = 0;
		}

		if (/*ts->size1 < BUFSIZE &&*/
			FD_ISSET(ts->sockfd_read, &rdfdset)) {
#ifdef ATLAS
			if (ts->size1 < BUFSIZE &&
				(ts->rdidx1 >= BUFSIZE ||
				ts->rdidx1 < ts->wridx1))
			{
				pack_2pty(ts);
			}
#endif

			/* Read from socket to buffer 1. */
			count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);

			count = safe_read(ts->sockfd_read,
				TS_BUF1 + ts->rdidx1, count);
			if (count <= 0) {
				if (count < 0 && errno == EAGAIN)
					goto skip3;
				goto kill_session;
			}
			/* Ignore trailing NUL if it is there */
			if (!TS_BUF1[ts->rdidx1 + count - 1]) {
				--count;
			}
			ts->size1 += count;
			ts->rdidx1 += count;
			if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
				ts->rdidx1 = 0;
		}
 skip3:
#ifdef ATLAS
		switch(ts->state)
		{
		case DO_TRADITIONAL:
			break;	/* Nothing to do */
		case GET_LOGINNAME:
			{
			unsigned char *ptr;

			ptr = remove_iacs(ts, &num_totty);

			line= getline_2pty(ts);
			if (!line)
				goto skip3a;

			if (strcmp(line, ATLAS_LOGIN) == 0)
			{
				free(line); line= NULL;
				add_2sock(ts, PASSWORD_PROMPT);
				ts->state= GET_PASSWORD;
				goto skip3;
			}
			else
			{
				int r;

				/* Echo login name */
				add_2sock(ts, line);

				r= start_login(ts, line);
				free(line); line= NULL;
				if (r == -1)
					goto kill_session;
				ts->state= DO_TRADITIONAL;
				goto skip3a;
			}

			}
		case GET_PASSWORD:
			remove_iacs(ts, &num_totty);

			line= getline_2pty(ts);
			if (!line)
				goto skip3a;

			if (equal_sessionid(line))
			{
				free(line); line= NULL;

				if (atlas_ts)
				{
					bb_error_msg("found atlas session");
					/* There is an old session still
					 * around. Take over.
					 */
					if (atlas_crontab)
					{
						fclose(atlas_crontab);
						atlas_crontab= NULL;
					}
				}
				atlas_ts= ts;
 
				ts->state= GET_CMD;
				goto skip3;
			}
			else
			{
				free(line); line= NULL;

				/* Bad password, the end */
				add_2sock(ts, BAD_PASSWORD);
				goto skip3;
			}

		case GET_CMD:
			{
			int r;
			size_t len;

			if (ts != atlas_ts)
				goto kill_session;	/* Old session */

			remove_iacs(ts, &num_totty);

			line= getline_2pty(ts);
			if (!line)
				goto skip3a;

do_cmd:
			len= strlen(CMD_CRONTAB);
			if (strncmp(line, CMD_CRONTAB, len) == 0)
			{
				r= start_crontab(ts, line);
				free(line); line= NULL;
				if (r == -1)
				{
					/* Assume start_crontab sent an
					 * error response.
					 */
					goto skip3;
				}

				ts->state= DO_CRONTAB;
				goto skip3;
			}

			len= strlen(CMD_ONEOFF);
			if (strncmp(line, CMD_ONEOFF, len) == 0)
			{
				do_oneoff(ts, line);
				free(line); line= NULL;

				/* Assume do_oneoff sent an error response
				 * if something was wrong.
				 */
				goto skip3;
			}
			if (strcmp(line, CMD_REBOOT) == 0)
			{
				sync();
				reboot(LINUX_REBOOT_CMD_RESTART);
				free(line); line= NULL;

				goto skip3;
			}
			if (strlen(line) == 0)
			{
				free(line); line= NULL;

				/* End of request */
				add_2sock(ts, RESULT_OK);

				ts->state= EOM_SEEN;
				goto skip3;
			}

			free(line); line= NULL;

			/* Bad command */
			add_2sock(ts, BAD_COMMAND);
			goto skip3a;
			}

		case DO_CRONTAB:
			{
			size_t len;

			if (ts != atlas_ts)
				goto kill_session;	/* Old session */

			remove_iacs(ts, &num_totty);

			line= getline_2pty(ts);
			if (!line)
				goto skip3a;

			len= strlen(CMD_CRONLINE);
			if (strncmp(line, CMD_CRONLINE, len) != 0)
			{
				end_crontab(ts);
				
				/* Assume end_crontab sends a response
				 * if there was an error.
				 */

				ts->state= GET_CMD;

				/* Unfortunately, the line that ends the
				 * crontab is the next command.
				 */
				goto do_cmd;
			}

			add_to_crontab(ts, line+len);
			free(line); line= NULL;

			/* And again */
			goto skip3;
			}

		case EOM_SEEN:
			if (ts != atlas_ts)
				goto kill_session;	/* Old session */

			/* Just eat all input and return bad command */
			remove_iacs(ts, &num_totty);

			line= getline_2pty(ts);
			if (!line)
				goto skip3a;

			free(line); line= NULL;
			add_2sock(ts, BAD_COMMAND);
			goto skip3;

		default:
			bb_error_msg("unknown state %d", ts->state);
			abort();
		}
skip3a:
#endif /* ATLAS */
		if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
			/* Read from pty to buffer 2. */
			count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
			count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
			if (count <= 0) {
				if (count < 0 && errno == EAGAIN)
					goto skip4;
				goto kill_session;
			}
			ts->size2 += count;
			ts->rdidx2 += count;
			if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
				ts->rdidx2 = 0;
		}
 skip4:
		ts = next;
		continue;
 kill_session:
#ifdef ATLAS
		if (ts == atlas_ts)
		{
			if (atlas_crontab)
			{
				fclose(atlas_crontab);
				atlas_crontab= NULL;
			}
			atlas_ts= NULL;
		}
#endif /* ATLAS */
		free_session(ts);
		ts = next;
	}

	goto again;
}

#ifdef ATLAS
static int equal_sessionid(char *passwd)
{
	size_t len;
	char *cp;
	FILE *file;
	char line[80];

	file= fopen(ATLAS_SESSION_FILE, "r");
	if (file == NULL)
	{
		syslog(LOG_ERR, "unable to open '%s': %m", ATLAS_SESSION_FILE);
		return 0;
	}

	fgets(line, sizeof(line), file);	/* Skip first empty line */
	if (fgets(line, sizeof(line), file) == NULL)
	{
		syslog(LOG_ERR, "unable to read from '%s': %m",
			ATLAS_SESSION_FILE);
		fclose(file);
		return 0;
	}
	fclose(file);

	len= strlen(SESSION_ID_PREFIX);
	if (strlen(line) < len)
	{
		syslog(LOG_ERR, "not enough session ID data");
		return 0;
	}
	if (memcmp(line, SESSION_ID_PREFIX, len) != 0)
	{
		syslog(LOG_ERR, "missing session ID prefix");
		return 0;
	}
		
	cp= strchr(line, '\n');
	if (cp == NULL)
	{
		syslog(LOG_ERR, "missing newline in session ID file");
		return 0;
	}
	*cp= '\0';

	if (strcmp(line+len, passwd) == 0)
		return 1;

	/* Wrong password */
	return 0;
}

static void add_2sock(struct tsession *ts, const char *str)
{
	size_t len;

	len= strlen(str);
	if (ts->size2 + len > BUFSIZE)
	{
		syslog(LOG_ERR, "add_2sock: buffer full");
		abort();
	}
	if (ts->rdidx2 + len > BUFSIZE)
		pack_4sock();

	memcpy(TS_BUF2+ts->rdidx2, str, len);
	ts->rdidx2 += len;
	ts->size2 += len;
}

static void pack_4sock(void)
{
	syslog(LOG_ERR, "pack_4sock: not implemented");
	abort();
}

static char *getline_2pty(struct tsession *ts)
{
	size_t size1, len;
	char *cp, *cp2, *line;

	size1= ts->size1;


	if (ts->wridx1 + size1 > BUFSIZE)
		pack_2pty(ts);

	/* remove_iacs converts a CR-LF to a CR */
	cp= memchr(TS_BUF1+ts->wridx1, '\r', size1);
	cp2= memchr(TS_BUF1+ts->wridx1, '\n', size1);
	if (cp2 != NULL && (cp == NULL || cp2 < cp))
	{
		/* Use the LF. Patch '\n' to '\r' */
		*cp2= '\r';
		cp= cp2;
	}
	if (cp == NULL)
		return NULL;

	len= cp-((char *)TS_BUF1+ts->wridx1)+1;
	line= xmalloc(len+1);
	memcpy(line, (char *)TS_BUF1+ts->wridx1, len);
	line[len]= '\0';

	ts->wridx1 += len;
	ts->size1 -= len;

	/* Make sure that the line ends in a \r. If not, just ignore the
	 * line. Otherwise, delete the \r.
	 */
	cp= strchr(line, '\r');
	if (cp == NULL || cp-line != strlen(line)-1)
	{
		bb_error_msg("bad line '%s', cp %p, cp-line %ld, |line| %ld",
			line, cp, (long)(cp-line), (long)strlen(line));

		/* Bad line, just ignore it */
		free(line); line= NULL;
		return NULL;
	}
	*cp= '\0';

	return line;
}

static void pack_2pty(struct tsession *ts)
{
	size_t size1, size_lo, size_hi, wridx1;

	size1= ts->size1;
	wridx1= ts->wridx1;

	size_hi= BUFSIZE-wridx1;	/* Amount at the top of the buffer */
	size_lo= size1-size_hi;

	/* Move the low part up a bit */
	memmove(TS_BUF1+size_hi, TS_BUF1, size_lo);

	/* Now move the high part down */
	memmove(TS_BUF1, TS_BUF1+wridx1, size_hi);

	/* Update wridx1 and rdidx1 */
	ts->wridx1= 0;
	ts->rdidx1= size1;
}

static int start_crontab(struct tsession *ts, char *line)
{
	size_t len;
	char *cp;
	char filename[256];

	if (atlas_crontab)
	{
		add_2sock(ts, CRONTAB_BUSY);
		return -1;
	}

	cp= line+strlen(CMD_CRONTAB);
	len= strlen(cp);
	if (len+1 > sizeof(atlas_dirname))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return -1;
	}
	strlcpy(atlas_dirname, cp, sizeof(atlas_dirname));

	if (len + strlen(CRONTAB_NEW_SUF) + 1 > sizeof(filename))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return -1;
	}

	strlcpy(filename, atlas_dirname, sizeof(filename));
	strlcat(filename, CRONTAB_NEW_SUF, sizeof(filename));

	if (!validate_filename(filename, SAFE_PREFIX))
	{
		add_2sock(ts, BAD_PATH);
		return -1;
	}

	atlas_crontab= fopen(filename, "w");
	if (!atlas_crontab)
	{
		add_2sock(ts, CREATE_FAILED);
		return -1;
	}

	return 0;
}

static void add_to_crontab(struct tsession *ts, char *line)
{
	if (!atlas_crontab)
		return;		/* Some error occured earlier */
	// fprintf(stderr, "telnetd: adding '%s' to crontab\n", line);
	if (fputs(line, atlas_crontab) == -1 || 
		fputc('\n', atlas_crontab) == -1)
	{
		add_2sock(ts, IO_ERROR);
		fclose(atlas_crontab);
		atlas_crontab= NULL;
		return;
	}
}

static void end_crontab(struct tsession *ts)
{
	int fd;
	size_t len;
	struct stat st;
	char filename1[256];
	char filename2[256];

	if (!atlas_crontab)
		return;		/* Some error occured earlier */
	if (fclose(atlas_crontab) == -1)
	{
		atlas_crontab= NULL;
		add_2sock(ts, IO_ERROR);
		return;
	}
	atlas_crontab= NULL;

	/* Rename */
	len= strlen(atlas_dirname);
	if (len + strlen(CRONTAB_NEW_SUF) + 1 > sizeof(filename1))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return;
	}
	strlcpy(filename1, atlas_dirname, sizeof(filename1));
	strlcat(filename1, CRONTAB_NEW_SUF, sizeof(filename1));
	if (len + strlen(CRONTAB_SUFFIX) + 1 > sizeof(filename2))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return;
	}
	strlcpy(filename2, atlas_dirname, sizeof(filename2));
	strlcat(filename2, CRONTAB_SUFFIX, sizeof(filename2));
	if (rename(filename1, filename2) == -1)
	{
		add_2sock(ts, IO_ERROR);
		return;
	}

	/* Inspired by the crontab command, tell cron to load the new
	 * crontab.
	 */
	if (strlen(atlas_dirname) + strlen(CRONUPDATE) + 1 > sizeof(filename1))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return;
	}

	strlcpy(filename1, atlas_dirname, sizeof(filename1));
	strlcat(filename1, CRONUPDATE, sizeof(filename1));

	while (fd= open(filename1, O_WRONLY|O_CREAT|O_TRUNC, 0600), fd >= 0)
	{
		len= strlen(UPDATELINE);
		if (write(fd, UPDATELINE, len) != len)
		{
			close(fd);
			add_2sock(ts, IO_ERROR);
			return;
		}
		if (fstat(fd, &st) != 0)
		{
			close(fd);
			add_2sock(ts, IO_ERROR);
			return;
		}
		close(fd);
		if (st.st_nlink != 0)
			break;

		/* Race condition, try again */
	}

	if (fd < 0)
	{
		add_2sock(ts, CREATE_FAILED);
		return;
	}
}

static void do_oneoff(struct tsession *ts, char *line)
{
	size_t len;
	char *cp, *ncp;
	FILE *file;
	char filename[256];
	char filename_new[256];

	cp= line+strlen(CMD_ONEOFF);

	/* Find the end of the filename */
	ncp= cp;
	while (ncp[0] != '\0' && !isspace((unsigned char)ncp[0]))
		ncp++;

	len= ncp-cp;
	if (len+1 > sizeof(filename))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return;
	}
	memcpy(filename, cp, len);
	filename[len]= '\0';

	if (len + strlen(ONEOFF_SUFFIX) + 1 > sizeof(filename_new))
	{
		add_2sock(ts, NAME_TOO_LONG);
		return;
	}
	strlcpy(filename_new, filename, sizeof(filename_new));
	strlcat(filename_new, ONEOFF_SUFFIX, sizeof(filename_new));

	if (!validate_filename(filename, SAFE_PREFIX))
	{
		add_2sock(ts, BAD_PATH);
		return;
	}

	/* Try to grab 'filename', if there is any. It doesn't matter if this
	 * fails.
	 */
	rename(filename, filename_new);

	file= fopen(filename_new, "a");
	if (!file)
	{
		add_2sock(ts, CREATE_FAILED);
		return;
	}

	/* Find start of command */
	cp= ncp;
	while (cp[0] != '\0' && isspace((unsigned char)cp[0]))
		cp++;

	if (fprintf(file, "%s\n", cp) == -1)
	{
		add_2sock(ts, IO_ERROR);
		fclose(file);
		return;
	}

	fclose(file);

	/* And rename back. Ignore any errors */
	rename(filename_new, filename);
}

#endif /* ATLAS */