Re: [PATCH] TTY: do not reset master's packet mode

From: Jiri Slaby
Date: Wed Feb 20 2013 - 11:40:42 EST

On 02/20/2013 02:19 PM, Karel Zak wrote:
> On Tue, Jan 15, 2013 at 11:26:22PM +0100, Jiri Slaby wrote:
>> Now that login from util-linux is forced to drop all references to a
>> TTY which it wants to hangup (to reach reference count 1) we are
>> seeing issues with telnet. When login closes its last reference to the
>> slave PTY, it also resets packet mode on the *master* side. And we
>> have a race here.
> [...]
>> By this I am resurrecting an old bug, see References. We are hitting
>> it regularly now, i.e. with updated util-linux, ergo login.
>> Here, I am changing a behavior introduced back in 2.1 times. It would
>> better have a long time testing before goes upstream.
> It would be nice to found a quick way how to resolve this problem,
> because telnet+login is broken now... and for end users it seems like
> a regression.

Oh, the patch is in the TTY tree and I suppose it will go to 3.9-rc1
(and to stable as we will get to same later -rc -- to have some testing).

> Maybe the requirement (patch) to close all references to TTY before
> hangup should reverted or we can make an exception in login(1) code to
> keep TTY open when login(1) is executed with -h (as used by telned).

If we reverted the patch in login, we would have to revert also a patch
in the TTY which closes a window allowing you to crash a kernel at will
(in fact that patch disallows multiple opens when hanging up a terminal.
IOW only the one to hang the terminal is allowed to have it opened.)

suse labs
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