Re: [bug-inetutils] Telnetd fails to handle some of TIOCPKT control bytes.

[Takashi Yano]

Thank you for your reply.

With your patch, I have confirmed the problem has disappeared.

However, I am a little bit concerned about calling pty_get_char(0)
twice in the case of TIOCPKT_FLUSHWRITE or TIOCPKT_IOCTL.

Is it intentional behaviour?


On Sat, 21 Mar 2015 19:44:45 +0100
Mats Erik Andersson <address@hidden> wrote:

> Saturday den 28 February 2015 klockan 14:15 skrev Takashi Yano detta:
> > Package: inetutils
> > Version: 1.9.2 or older
> > 
> > Telnetd in inetutils package lacks handling of some of TIOCPKT
> > control bytes. The most influential thing is a lack of handling
> > of TIOCPKT_DATA. TIOCPKT_DATAs i.e. '\0's frequently appear in
> > the stream of network side. TIOCPKT_FLUSHREAD, TIOCPKT_STOP and
> > TIOPKT_START leak out into network side too.
> > 
> > To fix this problem, I have made following patch.
> > 
> > In this patch, the first byte from read() is always treated as
> > a TIOCPKT control byte. Therefore, it is simply read out instead
> > of being peeked. This is based on description in man tty_ioctl,
> > which says the first byte returned by read() is always a TIOCPKT
> > control byte.
> > 
> 
> These are all valid observations.  Based on previous messages
> on this issue and on your discussion, I arrived at a solution
> which has been pushed to the development head.  The relevant
> changes to inetutils-1.9.2 are reproduced below.  Exactly as
> you have observed, the issue boils down to a call pty_get_char(0)
> which got hidden in a subcase, instead of being executed every
> time the PTY delivered a packet.
> 
> Thanks for bringing the matter to my attentions (I had lost
> contact with the list from November 28th until this week!)
> 
> Best regards,
>   Mats Erik Andersson
> 
> 
> --- telnetd/telnetd.c.orig
> +++ telnetd/telnetd.c
> @@ -658,7 +658,7 @@
>        if (FD_ISSET (pty, &ibits))
>       {
>         /* Something to read from the pty... */
> -       if (pty_read () < 0)
> +       if (pty_read () <= 0)
>           break;
>         c = pty_get_char (1);
>  #if defined TIOCPKT_IOCTL
> @@ -689,9 +689,8 @@
>                                  IAC, SB, TELOPT_LFLOW,
>                                  flowmode ? LFLOW_ON : LFLOW_OFF, IAC, SE);
>               }
> -           pty_get_char (0);
>           }
> -
> +       pty_get_char (0);
>       }
>  
>        while (pty_input_level () > 0)


-- 
Takashi Yano <address@hidden>