telnetd.c

经典的unix下telnetd代码

	    close(t);
	}
    }
#endif

    show_issue();
    /*
     * 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;

    if (cgetent(&buf, gettytab, gettyent) >= 0) {
	char *HN;

	if (cgetstr(buf, "he", &he) <= 0)
	    he = NULL;
	if (cgetstr(buf, "im", &IM) <= 0)
	    IM = "";
	if (cgetstr(buf, "hn", &HN) > 0) {
	    strlcpy(host_name, HN, sizeof host_name);
	    free(HN);
	}
	cgetclose();
    } else {
	IM = DEFAULT_IM;
	he = NULL;
    }
    edithost(he, host_name);
    if (he)
	free(he);
    if (hostinfo && *IM)
	putf(IM, ptyibuf2);
    if (IM != DEFAULT_IM && *IM)
	free(IM);

    if (pcc)
	strncat(ptyibuf2, ptyip, pcc+1);
    ptyip = ptyibuf2;
    pcc = strlen(ptyip);

    DIAG(TD_REPORT, {
	output_data("td: Entering processing loop\r\n");
    });


    nfd = ((f > p) ? f : p) + 1;
    setsize = howmany(nfd, NFDBITS) * sizeof(fd_mask);
    ibits = malloc(setsize);
    obits = malloc(setsize);
    xbits = malloc(setsize);
    if (ibits == NULL || obits == NULL || xbits == NULL) {
	syslog(LOG_ERR, "Out of memory");
	exit(1);
    }
    timeout = time(NULL) + 5;
    for (;;) {
	int c;

	/* wait for encryption to be turned on, but don't wait
           indefinitely */
	if(!startslave_called && (!encrypt_delay() || timeout > time(NULL))){
	    startslave_called = 1;
	    startslave(host, utmp_host, level, autoname);
	}

	if (ncc < 0 && pcc < 0)
	    break;

	memset(obits, 0, setsize);
	memset(ibits, 0, setsize);
	memset(xbits, 0, setsize);

	/*
	 * Never look for input if there's still
	 * stuff in the corresponding output buffer
	 */
	if (nfrontp - nbackp || pcc > 0) {
	    FD_SET(f, obits);
	} else {
	    FD_SET(p, ibits);
	}
	if (pfrontp - pbackp || ncc > 0) {
	    FD_SET(p, obits);
	} else {
	    FD_SET(f, ibits);
	}
	if (!SYNCHing) {
	    FD_SET(f, xbits);
	}
	if ((c = select(nfd, ibits, obits, xbits,
			(struct timeval *)0)) < 1) {
	    if (c == -1) {
		if (errno == EINTR) {
		    continue;
		}
	    }
	    sleep(5);
	    continue;
	}

	/*
	 * Any urgent data?
	 */
	if (FD_ISSET(f, xbits)) {
	    SYNCHing = 1;
	}

	/*
	 * Something to read from the network...
	 */
	if (FD_ISSET(f, ibits)) {
#ifndef 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(f, SIOCATMARK, (char *)&atmark);
		if (atmark) {
		    ncc = recv(f, netibuf, sizeof (netibuf), MSG_OOB);
		    if ((ncc == -1) && (errno == EINVAL)) {
			ncc = read(f, netibuf, sizeof (netibuf));
			if (sequenceIs(didnetreceive, gotDM)) {
			    SYNCHing = stilloob(f);
			}
		    }
		} else {
		    ncc = read(f, netibuf, sizeof (netibuf));
		}
	    } else {
		ncc = read(f, 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), {
		output_data("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)) {
#ifdef STREAMSPTY
	    if (really_stream)
		pcc = readstream(p, ptyibuf, BUFSIZ);
	    else
#endif
		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 ||
#ifdef	EAGAIN
			    errno == EAGAIN ||
#endif
			    errno == EIO)) {
		pcc = 0;
	    } else {
		if (pcc <= 0)
		    break;
		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.
		     */
		    output_data ("%c%c", IAC, DM);

		    neturg = nfrontp-1; /* off by one XXX */
		    DIAG(TD_OPTIONS,
			 printoption("td: send IAC", DM));

#endif
		}
		if (his_state_is_will(TELOPT_LFLOW) &&
		    (ptyibuf[0] &
		     (TIOCPKT_NOSTOP|TIOCPKT_DOSTOP))) {
		    int newflow =
			ptyibuf[0] & TIOCPKT_DOSTOP ? 1 : 0;
		    if (newflow != flowmode) {
			flowmode = newflow;
			output_data("%c%c%c%c%c%c",
				    IAC, SB, TELOPT_LFLOW,
				    flowmode ? LFLOW_ON
				    : LFLOW_OFF,
				    IAC, SE);
			DIAG(TD_OPTIONS, printsub('>',
						  (unsigned char *)nfrontp-4,
						  4););
		    }
		}
		pcc--;
		ptyip = ptyibuf+1;
	    }
	}

	while (pcc > 0) {
	    if ((&netobuf[BUFSIZ] - nfrontp) < 3)
		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);
}

#ifndef	TCSIG
# ifdef	TIOCSIG
#  define TCSIG TIOCSIG
# endif
#endif

#ifdef	STREAMSPTY

    int flowison = -1;  /* current state of flow: -1 is unknown */

int
readstream(int p, char *ibuf, int bufsize)
{
    int flags = 0;
    int ret = 0;
    struct termios *tsp;
#if 0
    struct termio *tp;
#endif
    struct iocblk *ip;
    char vstop, vstart;
    int ixon;
    int newflow;

    strbufc.maxlen = BUFSIZ;
    strbufc.buf = (char *)ctlbuf;
    strbufd.maxlen = bufsize-1;
    strbufd.len = 0;
    strbufd.buf = ibuf+1;
    ibuf[0] = 0;

    ret = getmsg(p, &strbufc, &strbufd, &flags);
    if (ret < 0)  /* error of some sort -- probably EAGAIN */
	return(-1);

    if (strbufc.len <= 0 || ctlbuf[0] == M_DATA) {
	/* data message */
	if (strbufd.len > 0) {			/* real data */
	    return(strbufd.len + 1);	/* count header char */
	} else {
	    /* nothing there */
	    errno = EAGAIN;
	    return(-1);
	}
    }

    /*
     * It's a control message.  Return 1, to look at the flag we set
     */

    switch (ctlbuf[0]) {
    case M_FLUSH:
	if (ibuf[1] & FLUSHW)
	    ibuf[0] = TIOCPKT_FLUSHWRITE;
	return(1);

    case M_IOCTL:
	ip = (struct iocblk *) (ibuf+1);

	switch (ip->ioc_cmd) {
#ifdef TCSETS
	case TCSETS:
	case TCSETSW:
	case TCSETSF:
	    tsp = (struct termios *)
		(ibuf+1 + sizeof(struct iocblk));
	    vstop = tsp->c_cc[VSTOP];
	    vstart = tsp->c_cc[VSTART];
	    ixon = tsp->c_iflag & IXON;
	    break;
#endif
#if 0
	case TCSETA:
	case TCSETAW:
	case TCSETAF:
	    tp = (struct termio *) (ibuf+1 + sizeof(struct iocblk));
	    vstop = tp->c_cc[VSTOP];
	    vstart = tp->c_cc[VSTART];
	    ixon = tp->c_iflag & IXON;
	    break;
#endif
	default:
	    errno = EAGAIN;
	    return(-1);
	}

	newflow =  (ixon && (vstart == 021) && (vstop == 023)) ? 1 : 0;
	if (newflow != flowison) {  /* it's a change */
	    flowison = newflow;
	    ibuf[0] = newflow ? TIOCPKT_DOSTOP : TIOCPKT_NOSTOP;
	    return(1);
	}
    }

    /* nothing worth doing anything about */
    errno = EAGAIN;
    return(-1);
}
#endif /* STREAMSPTY */

/*
 * Send interrupt to process on other side of pty.
 * If it is in raw mode, just write NULL;
 * otherwise, write intr char.
 */
void
interrupt()
{
    ptyflush();	/* half-hearted */

#if defined(STREAMSPTY) && defined(TIOCSIGNAL)
    /* Streams PTY style ioctl to post a signal */
    if (really_stream)
	{
	    int sig = SIGINT;
	    ioctl(ourpty, TIOCSIGNAL, &sig);
	    ioctl(ourpty, I_FLUSH, FLUSHR);
	}
#else
#ifdef	TCSIG
    ioctl(ourpty, TCSIG, (char *)SIGINT);
#else	/* TCSIG */
    init_termbuf();
    *pfrontp++ = slctab[SLC_IP].sptr ?
	(unsigned char)*slctab[SLC_IP].sptr : '\177';
#endif	/* TCSIG */
#endif
}

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

void
sendsusp()
{
#ifdef	SIGTSTP
    ptyflush();	/* half-hearted */
# ifdef	TCSIG
    ioctl(ourpty, 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()
{
#if	defined(SIGINFO) && defined(TCSIG)
    if (slctab[SLC_AYT].sptr && *slctab[SLC_AYT].sptr != _POSIX_VDISABLE) {
	ioctl(ourpty, TCSIG, (char *)SIGINFO);
	return;
    }
#endif
    output_data("\r\n[Yes]\r\n");
}

void
doeof()
{
    init_termbuf();

    *pfrontp++ = slctab[SLC_EOF].sptr ?
	(unsigned char)*slctab[SLC_EOF].sptr : '\004';
}