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From Sun Jan 26 14:48:33 1997
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Date: Sun, 26 Jan 1997 14:48:28 -0500 (EST)
From: Ken Hornstein <>
To: krb5-bugs@MIT.EDU
Subject: IRIX bug in pty packet mode handling causes mangled login prompt
X-Send-Pr-Version: 3.99

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>Number: 353
>Category: krb5-appl
>Synopsis: A bug in IRIX pty packet mode handling cases a mangled login prompt
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: krb5-unassigned
>State: open
>Class: change-request
>Submitter-Id: unknown
>Arrival-Date: Sun Jan 26 14:49:01 EST 1997
>Originator: Ken Hornstein
Navel Research Lab

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>Release: 1.0

System: IRIX borg 5.3
Architecture: mips

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There is a bug in IRIX w.r.t. pty packet mode. The gist of the bug is that
if data is written to a slave _before_ a pty is switched into packet mode,
it will be output on the master without a control byte even if the master
gets switched into packet mode later.

So, how does this affect Kerberos 5? This generates a race condition with
the Kerberos login program and telnetd. If the login program prints a
prompt before telnetd switches the master pty into packet mode, then
the first character will get eaten. This becomes more noticable if you
remove the "sleep(2)" inside of the login program.

While normally this just results in a "ogin: " prompt, depending on your
telnet client you can occasionally get a "assword for user:" prompt, which
is ... unexpected at best, and potentially insulting at worst :-)
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Run the Kerberos login/telnetd under Irix for a while. Or use this example
program to demonstrate the bug (yes, it's a gross program, but what do
you expect for a five-minute hack? :-) ).

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>

main(int argc, char *argv[])
char *master = NULL;
char *slave;
int masterfd, slavefd, i = 1;
char buf[256];

#ifdef sgi

slave = _getpty(&masterfd, O_RDWR|O_NDELAY, 0600, 0);

if (! slave) {
fprintf(stderr, "Cannot get pty, exiting\n");

if ((slavefd = open(slave, O_RDWR)) < 0) {
fprintf(stderr, "Cannot open slave, exiting\n");
master = "/dev/ptyr0";
slave = "/dev/ttyr0";

if ((masterfd = open(master, O_RDWR|O_NDELAY, 0600)) < 0) {
fprintf(stderr, "Cannot open master, exiting\n");

if ((slavefd = open(slave, O_RDWR|O_NDELAY, 0600)) < 0) {
fprintf(stderr, "Cannot open slave, exiting\n");
if (master)
printf("master pty = %s\n", master);
printf("slave pty = %s\n", slave);

printf("Writing data on slave pty ...\n");

write (slavefd, "hello", strlen("hello"));

printf("Switching master into packet mode...\n");

ioctl(masterfd, TIOCPKT, &i);

printf("Reading data from master ...\n");

i = read(masterfd, buf, 999);

printf("I got %d bytes, first byte was %02x\n", i, buf[0]);

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My solution was to add an "#ifdef sgi ... fputc('\0') ... #endif" at the
appropriate spots in login. I'm not sure what the right thing to do is.
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