linux-kernel - Re: [ 02/42] TTY: do not update atime/mtime on read/write

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Date:	Tue, 30 Apr 2013 16:50:53 -0700
From:	Simon Kirby <sim@...tway.ca>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [ 02/42] TTY: do not update atime/mtime on read/write

On Mon, Apr 29, 2013 at 06:37:24PM -0700, Greg Kroah-Hartman wrote:

> On Mon, Apr 29, 2013 at 05:36:40PM -0700, Simon Kirby wrote:
> > On Mon, Apr 29, 2013 at 05:21:17PM -0700, Greg Kroah-Hartman wrote:
> > 
> > > On Mon, Apr 29, 2013 at 05:14:45PM -0700, Simon Kirby wrote:
> > > > On Mon, Apr 29, 2013 at 12:01:44PM -0700, Greg Kroah-Hartman wrote:
> > > > 
> > > > > 3.8-stable review patch.  If anyone has any objections, please let me know.
> > > > 
> > > > I object. This breaks functionality I use every day (seeing who else is
> > > > working on stuff with "w").
> > > > 
> > > > Furthermore, the patch does not actually fix the hole referenced (see
> > > > ptmx-keystroke-latency.c on http://vladz.devzero.fr/013_ptmx-timing.php).
> > > > I can still reproduce the timing capture even with this patch applied
> > > > (in 3.9-rc8).
> > > 
> > > How?  There are no keystrokes being reported to other users, or did we
> > > miss something with this patch?
> > 
> > wget http://vladz.devzero.fr/svn/codes/PoC/ptmx-keystroke-latency.c
> > gcc -O ptmx-keystroke-latency ptmx-keystroke-latency.c
> > ./ptmx-keystroke-latency
> > 
> > Log in to another tty, as another user. See keystroke timing. 3.9-rc8.
> > 
> > Seems like it was missed. Meanwhile, idle times in "w" do not update.
> 
> Ah, it's using inotify on the /dev/ptmx device.  Jiri, your change
> really doesn't affect that at all :(
> 
> Simon, you mention a grsec change somewhere that addresses this issue.
> Any hints on where that would be?

Yes, see Jiri's comments in the original patch (b0de59b5733d):

http://vladz.devzero.fr/013_ptmx-timing.php

The grsec patch is linked from there:

http://grsecurity.net/~spender/sidechannel.diff

Simon-
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