telnetd.c

这是关于远程登陆TELNET 的源代码 已经测试过的。

    /*
     * Don't do this - tgetent is not really trustworthy. Assume
     * the terminal type is one we know; terminal types are pretty
     * standard now. And if it isn't, it's unlikely we're going to
     * know anything else the remote telnet might send as an alias
     * for it.
     *
     * if (tgetent(buf, s) == 0)
     *    return(0);
     */
    return(1);
}

#ifndef	MAXHOSTNAMELEN
#define	MAXHOSTNAMELEN 64
#endif	/* MAXHOSTNAMELEN */

char host_name[MAXHOSTNAMELEN];
char remote_host_name[MAXHOSTNAMELEN];

extern void telnet(int, int);

/*
 * Get a pty, scan input lines.
 */
static void
doit(struct sockaddr_in *who)
{
	const char *host;
	struct hostent *hp;
	int level;
	char user_name[256];

	/*
	 * Find an available pty to use.
	 */
	pty = getpty();
	if (pty < 0)
		fatal(net, "All network ports in use");

	/* get name of connected client */
	hp = gethostbyaddr((char *)&who->sin_addr, sizeof (struct in_addr),
		who->sin_family);
	if (hp)
		host = hp->h_name;
	else
		host = inet_ntoa(who->sin_addr);

	/*
	 * We must make a copy because Kerberos is probably going
	 * to also do a gethost* and overwrite the static data...
	 */
	{
		int i;
		strncpy(remote_host_name, host, sizeof(remote_host_name)-1);
		remote_host_name[sizeof(remote_host_name)-1] = 0;

		/* Disallow funnies. */
		for (i=0; remote_host_name[i]; i++) {
		    if (remote_host_name[i]<=32 || remote_host_name[i]>126) 
			remote_host_name[i] = '?';
		}
	}
	host = remote_host_name;

	/* Get local host name */
	{
		struct hostent *h;
		gethostname(host_name, sizeof(host_name));
		h = gethostbyname(host_name);
		if (h) {
		    strncpy(host_name, h->h_name, sizeof(host_name));
		    host_name[sizeof(host_name)-1] = 0;
		}
	}

#if	defined(AUTHENTICATE) || defined(ENCRYPT)
	auth_encrypt_init(host_name, host, "TELNETD", 1);
#endif

	init_env();
	/*
	 * get terminal type.
	 */
	*user_name = 0;
	level = getterminaltype(user_name);
	setenv("TERM", terminaltype ? terminaltype : "network", 1);

	/* TODO list stuff provided by Laszlo Vecsey <[e-mail]> */

	/*
	 * Set REMOTEHOST environment variable
	 */
	setproctitle("%s", host);
	setenv("REMOTEHOST", host, 0);

	/*
	 * Start up the login process on the slave side of the terminal
	 */
	startslave(host, level, user_name);

	telnet(net, pty);  /* begin server processing */

	/*NOTREACHED*/
}  /* end of doit */

/*
 * Main loop.  Select from pty and network, and
 * hand data to telnet receiver finite state machine.
 */
void telnet(int f, int p)
{
    int on = 1;
    char *HE;
    const char *IM;

    /*
     * Initialize the slc mapping table.
     */
    get_slc_defaults();

    /*
     * Do some tests where it is desireable to wait for a response.
     * Rather than doing them slowly, one at a time, do them all
     * at once.
     */
    if (my_state_is_wont(TELOPT_SGA))
	send_will(TELOPT_SGA, 1);
    /*
     * Is the client side a 4.2 (NOT 4.3) system?  We need to know this
     * because 4.2 clients are unable to deal with TCP urgent data.
     *
     * To find out, we send out a "DO ECHO".  If the remote system
     * answers "WILL ECHO" it is probably a 4.2 client, and we note
     * that fact ("WILL ECHO" ==> that the client will echo what
     * WE, the server, sends it; it does NOT mean that the client will
     * echo the terminal input).
     */
    send_do(TELOPT_ECHO, 1);
    
#ifdef	LINEMODE
    if (his_state_is_wont(TELOPT_LINEMODE)) {
	/*
	 * Query the peer for linemode support by trying to negotiate
	 * the linemode option.
	 */
	linemode = 0;
	editmode = 0;
	send_do(TELOPT_LINEMODE, 1);  /* send do linemode */
    }
#endif	/* LINEMODE */

    /*
     * Send along a couple of other options that we wish to negotiate.
     */
    send_do(TELOPT_NAWS, 1);
    send_will(TELOPT_STATUS, 1);
    flowmode = 1;  /* default flow control state */
    send_do(TELOPT_LFLOW, 1);
    
    /*
     * Spin, waiting for a response from the DO ECHO.  However,
     * some REALLY DUMB telnets out there might not respond
     * to the DO ECHO.  So, we spin looking for NAWS, (most dumb
     * telnets so far seem to respond with WONT for a DO that
     * they don't understand...) because by the time we get the
     * response, it will already have processed the DO ECHO.
     * Kludge upon kludge.
     */
    while (his_will_wont_is_changing(TELOPT_NAWS)) {
	ttloop();
    }
    
    /*
     * But...
     * The client might have sent a WILL NAWS as part of its
     * startup code; if so, we'll be here before we get the
     * response to the DO ECHO.  We'll make the assumption
     * that any implementation that understands about NAWS
     * is a modern enough implementation that it will respond
     * to our DO ECHO request; hence we'll do another spin
     * waiting for the ECHO option to settle down, which is
     * what we wanted to do in the first place...
     */
    if (his_want_state_is_will(TELOPT_ECHO) &&
	his_state_is_will(TELOPT_NAWS)) {
	while (his_will_wont_is_changing(TELOPT_ECHO))
	    ttloop();
    }
    /*
     * On the off chance that the telnet client is broken and does not
     * respond to the DO ECHO we sent, (after all, we did send the
     * DO NAWS negotiation after the DO ECHO, and we won't get here
     * until a response to the DO NAWS comes back) simulate the
     * receipt of a will echo.  This will also send a WONT ECHO
     * to the client, since we assume that the client failed to
     * respond because it believes that it is already in DO ECHO
     * mode, which we do not want.
     */
    if (his_want_state_is_will(TELOPT_ECHO)) {
	DIAG(TD_OPTIONS, netoprintf("td: simulating recv\r\n"););
	willoption(TELOPT_ECHO);
    }
    
    /*
     * Finally, to clean things up, we turn on our echo.  This
     * will break stupid 4.2 telnets out of local terminal echo.
     */
    
    if (my_state_is_wont(TELOPT_ECHO))
	send_will(TELOPT_ECHO, 1);
    
    /*
     * Turn on packet mode
     */
    ioctl(p, TIOCPKT, (char *)&on);
#if defined(LINEMODE) && defined(KLUDGELINEMODE)
    /*
     * Continuing line mode support.  If client does not support
     * real linemode, attempt to negotiate kludge linemode by sending
     * the do timing mark sequence.
     */
    if (lmodetype < REAL_LINEMODE)
	send_do(TELOPT_TM, 1);
#endif	/* defined(LINEMODE) && defined(KLUDGELINEMODE) */
    
    /*
     * Call telrcv() once to pick up anything received during
     * terminal type negotiation, 4.2/4.3 determination, and
     * linemode negotiation.
     */
    telrcv();
    
    ioctl(f, FIONBIO, (char *)&on);
    ioctl(p, FIONBIO, (char *)&on);

#if defined(SO_OOBINLINE)
    setsockopt(net, SOL_SOCKET, SO_OOBINLINE, &on, sizeof on);
#endif	/* defined(SO_OOBINLINE) */
    
#ifdef	SIGTSTP
    signal(SIGTSTP, SIG_IGN);
#endif
#ifdef	SIGTTOU
    /*
     * Ignoring SIGTTOU keeps the kernel from blocking us
     * in ttioct() in /sys/tty.c.
     */
    signal(SIGTTOU, SIG_IGN);
#endif
    
    signal(SIGCHLD, cleanup);
    
#ifdef TIOCNOTTY
    {
	register int t;
	t = open(_PATH_TTY, O_RDWR);
	if (t >= 0) {
	    (void) ioctl(t, TIOCNOTTY, (char *)0);
	    (void) close(t);
	}
    }
#endif
    
    /*
     * Show banner that getty never gave.
     *
     * We put the banner in the pty input buffer.  This way, it
     * gets carriage return null processing, etc., just like all
     * other pty --> client data.
     */
    
    if (getenv("USER"))
	hostinfo = 0;
    
    IM = DEFAULT_IM;
    HE = 0;

    edithost(HE, host_name);
    if (hostinfo && *IM)
	putf(IM, ptyibuf2);
    
    if (pcc) strncat(ptyibuf2, ptyip, pcc+1);
    ptyip = ptyibuf2;
    pcc = strlen(ptyip);
#ifdef LINEMODE
    /*
     * Last check to make sure all our states are correct.
     */
    init_termbuf();
    localstat();
#endif	/* LINEMODE */

    DIAG(TD_REPORT, netoprintf("td: Entering processing loop\r\n"););
    
    for (;;) {
	fd_set ibits, obits, xbits;
	int c, hifd;
	
	if (ncc < 0 && pcc < 0)
	    break;
	
	FD_ZERO(&ibits);
	FD_ZERO(&obits);
	FD_ZERO(&xbits);
	hifd=0;
	/*
	 * Never look for input if there's still
	 * stuff in the corresponding output buffer
	 */
	if (nfrontp - nbackp || pcc > 0) {
	    FD_SET(f, &obits);
	    if (f >= hifd) hifd = f+1;
	} 
	else {
	    FD_SET(p, &ibits);
	    if (p >= hifd) hifd = p+1;
	}
	if (pfrontp - pbackp || ncc > 0) {
	    FD_SET(p, &obits);
	    if (p >= hifd) hifd = p+1;
	} 
	else {
	    FD_SET(f, &ibits);
	    if (f >= hifd) hifd = f+1;
	}
	if (!SYNCHing) {
	    FD_SET(f, &xbits);
	    if (f >= hifd) hifd = f+1;
	}
	if ((c = select(hifd, &ibits, &obits, &xbits,
			(struct timeval *)0)) < 1) {
	    if (c == -1) {
		if (errno == EINTR) {
		    continue;
		}
	    }
	    sleep(5);
	    continue;
	}
	
	/*
	 * Any urgent data?
	 */
	if (FD_ISSET(net, &xbits)) {
	    SYNCHing = 1;
	}
	
	/*
	 * Something to read from the network...
	 */
	if (FD_ISSET(net, &ibits)) {
#if !defined(SO_OOBINLINE)
	    /*
	     * In 4.2 (and 4.3 beta) systems, the
	     * OOB indication and data handling in the kernel
	     * is such that if two separate TCP Urgent requests
	     * come in, one byte of TCP data will be overlaid.
	     * This is fatal for Telnet, but we try to live
	     * with it.
	     *
	     * In addition, in 4.2 (and...), a special protocol
	     * is needed to pick up the TCP Urgent data in
	     * the correct sequence.
	     *
	     * What we do is:  if we think we are in urgent
	     * mode, we look to see if we are "at the mark".
	     * If we are, we do an OOB receive.  If we run
	     * this twice, we will do the OOB receive twice,
	     * but the second will fail, since the second
	     * time we were "at the mark", but there wasn't
	     * any data there (the kernel doesn't reset
	     * "at the mark" until we do a normal read).
	     * Once we've read the OOB data, we go ahead
	     * and do normal reads.
	     *
	     * There is also another problem, which is that
	     * since the OOB byte we read doesn't put us
	     * out of OOB state, and since that byte is most
	     * likely the TELNET DM (data mark), we would
	     * stay in the TELNET SYNCH (SYNCHing) state.
	     * So, clocks to the rescue.  If we've "just"
	     * received a DM, then we test for the
	     * presence of OOB data when the receive OOB
	     * fails (and AFTER we did the normal mode read
	     * to clear "at the mark").
	     */
	    if (SYNCHing) {
		int atmark;
		
		ioctl(net, SIOCATMARK, (char *)&atmark);
		if (atmark) {
		    ncc = recv(net, netibuf, sizeof (netibuf), MSG_OOB);
		    if ((ncc == -1) && (errno == EINVAL)) {
			ncc = read(net, netibuf, sizeof (netibuf));
			if (sequenceIs(didnetreceive, gotDM)) {
			    SYNCHing = stilloob(net);
			}
		    }
		} 
		else {
		    ncc = read(net, netibuf, sizeof (netibuf));
		}
	    } 
	    else {
		ncc = read(net, netibuf, sizeof (netibuf));
	    }
	    settimer(didnetreceive);
#else	/* !defined(SO_OOBINLINE)) */
	    ncc = read(net, netibuf, sizeof (netibuf));
#endif	/* !defined(SO_OOBINLINE)) */
	    if (ncc < 0 && errno == EWOULDBLOCK)
		ncc = 0;
	    else {
		if (ncc <= 0) {
		    break;
		}
		netip = netibuf;
	    }
	    DIAG((TD_REPORT | TD_NETDATA),
		 netoprintf("td: netread %d chars\r\n", ncc););
	    DIAG(TD_NETDATA, printdata("nd", netip, ncc));
	}
	
	/*
	 * Something to read from the pty...
	 */
	if (FD_ISSET(p, &ibits)) {
	    pcc = read(p, ptyibuf, BUFSIZ);
	    /*
	     * On some systems, if we try to read something
	     * off the master side before the slave side is
	     * opened, we get EIO.
	     */
	    if (pcc < 0 && (errno == EWOULDBLOCK || errno == EIO)) {
		pcc = 0;
	    } 
	    else {
		if (pcc <= 0)
		    break;
#ifdef	LINEMODE
				/*
				 * If ioctl from pty, pass it through net
				 */
		if (ptyibuf[0] & TIOCPKT_IOCTL) {
		    copy_termbuf(ptyibuf+1, pcc-1);
		    localstat();
		    pcc = 1;
		}
#endif	/* LINEMODE */
		if (ptyibuf[0] & TIOCPKT_FLUSHWRITE) {
		    netclear();	/* clear buffer back */
#ifndef	NO_URGENT
		    /*
		     * There are client telnets on some
		     * operating systems get screwed up
		     * royally if we send them urgent
		     * mode data.
		     */
		    netoprintf("%c%c", IAC, DM);
		    neturg = nfrontp-1; /* off by one XXX */
#endif
		}
		if (his_state_is_will(TELOPT_LFLOW) &&
		    (ptyibuf[0] &
		     (TIOCPKT_NOSTOP|TIOCPKT_DOSTOP))) {
			netoprintf("%c%c%c%c%c%c",
				   IAC, SB, TELOPT_LFLOW,
				   ptyibuf[0] & TIOCPKT_DOSTOP ? 1 : 0,
				   IAC, SE);
		}
		pcc--;
		ptyip = ptyibuf+1;
	    }
	}
	
	while (pcc > 0) {
	    if ((&netobuf[BUFSIZ] - nfrontp) < 2)
		break;
	    c = *ptyip++ & 0377, pcc--;
	    if (c == IAC)
		*nfrontp++ = c;
	    *nfrontp++ = c;
	    if ((c == '\r'  ) && (my_state_is_wont(TELOPT_BINARY))) {
		if (pcc > 0 && ((*ptyip & 0377) == '\n')) {
		    *nfrontp++ = *ptyip++ & 0377;
		    pcc--;
		} 
		else *nfrontp++ = '\0';
	    }
	}

	if (FD_ISSET(f, &obits) && (nfrontp - nbackp) > 0)
	    netflush();
	if (ncc > 0)
	    telrcv();
	if (FD_ISSET(p, &obits) && (pfrontp - pbackp) > 0)
	    ptyflush();
    }
    cleanup(0);
}  /* end of telnet */
	
#ifndef	TCSIG
# ifdef	TIOCSIG
#  define TCSIG TIOCSIG
# endif
#endif

/*
 * Send interrupt to process on other side of pty.
 * If it is in raw mode, just write NULL;
 * otherwise, write intr char.
 */
void interrupt(void) {
    ptyflush();	/* half-hearted */
    
#ifdef	TCSIG
    (void) ioctl(pty, TCSIG, (char *)SIGINT);
#else	/* TCSIG */
    init_termbuf();
    *pfrontp++ = slctab[SLC_IP].sptr ?
	 (unsigned char)*slctab[SLC_IP].sptr : '\177';
#endif	/* TCSIG */
}

/*
 * Send quit to process on other side of pty.
 * If it is in raw mode, just write NULL;
 * otherwise, write quit char.
 */
void sendbrk(void) {
    ptyflush();	/* half-hearted */
#ifdef	TCSIG
    (void) ioctl(pty, TCSIG, (char *)SIGQUIT);
#else	/* TCSIG */
    init_termbuf();
    *pfrontp++ = slctab[SLC_ABORT].sptr ?
	 (unsigned char)*slctab[SLC_ABORT].sptr : '\034';
#endif	/* TCSIG */
}

void sendsusp(void) {
#ifdef	SIGTSTP
    ptyflush();	/* half-hearted */
# ifdef	TCSIG
    (void) ioctl(pty, TCSIG, (char *)SIGTSTP);
# else	/* TCSIG */
    *pfrontp++ = slctab[SLC_SUSP].sptr ?
	(unsigned char)*slctab[SLC_SUSP].sptr : '\032';
# endif	/* TCSIG */
#endif	/* SIGTSTP */
}

/*
 * When we get an AYT, if ^T is enabled, use that.  Otherwise,
 * just send back "[Yes]".
 */
void recv_ayt(void) {
#if	defined(SIGINFO) && defined(TCSIG)
    if (slctab[SLC_AYT].sptr && *slctab[SLC_AYT].sptr != _POSIX_VDISABLE) {
	(void) ioctl(pty, TCSIG, (char *)SIGINFO);
	return;
    }
#endif
    netoprintf("\r\n[%s : yes]\r\n", host_name);
}

void doeof(void) {
    init_termbuf();

#if	defined(LINEMODE) && (VEOF == VMIN)
    if (!tty_isediting()) {
	extern char oldeofc;
	*pfrontp++ = oldeofc;
	return;
    }
#endif
    *pfrontp++ = slctab[SLC_EOF].sptr ?
	     (unsigned char)*slctab[SLC_EOF].sptr : '\004';
}