linux-kernel - Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes

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Message-ID: <20100629145137.GD4175@outflux.net>
Date:	Tue, 29 Jun 2010 07:51:37 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Veaceslav Falico <vfalico@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Neil Horman <nhorman@...driver.com>,
	Roland McGrath <roland@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Stefani Seibold <stefani@...bold.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Paris <eparis@...hat.com>,
	James Morris <jmorris@...ei.org>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Dhaval Giani <dhaval.giani@...il.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Steve Grubb <sgrubb@...hat.com>,
	Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes

On Tue, Jun 29, 2010 at 10:36:50AM +0100, Alan Cox wrote:
> > Through get_task_comm() and many direct uses of task->comm in the kernel,
> > it is possible for escape codes and other non-printables to leak into
> > dmesg, syslog, etc.  In the worst case, these strings could be used to
> > attack administrators using vulnerable terminal emulators, and at least
> > cause confusion through the injection of \r characters.
> 
> If an administrator has a vulnerable terminal emulator they have other
> problems.

Totally agreed.

> Please do any filtering you must in the yama security module where it
> only affects that. One way to approach it without losing data within the
> module might be to use HTML style encoding within Yama so your own tools
> can undo the 'sanitizing' rather than losing information ?

I'm not interested in sanitizing this in Yama.  The use of task->comm via
printk was seen as a flaw.  I didn't agree (see above about terminal),
and suggested that if it was a flaw, it was a flaw with printk or
task->comm itself.  Since "fixing" both of those have been vetoed,
I have no more interest in the filtering.

What I do have interest in is fixing get_task_comm's use of buffers, which
is theoretically problematic in some future where someone accidentally
calls it with a buffer smaller than sizeof(task->comm).

I'll send a patch that only fixes that and leaves out the filtering.

-Kees

-- 
Kees Cook
Ubuntu Security Team
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