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

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Message-Id: <20100629115957.38BF.A69D9226@jp.fujitsu.com>
Date:	Tue, 29 Jun 2010 12:05:56 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	kosaki.motohiro@...fujitsu.com,
	Kees Cook <kees.cook@...onical.com>,
	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>,
	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>,
	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

> Am Freitag, den 25.06.2010, 08:56 +0900 schrieb KOSAKI Motohiro:
> > > 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.
> > > 
> > > This patch sanitizes task->comm to only contain printable characters
> > > when it is set.  Additionally, it redefines get_task_comm so that it is
> > > more obvious when misused by callers (presently nothing was incorrectly
> > > calling get_task_comm's unsafe use of strncpy).
> > > 
> > > Signed-off-by: Kees Cook <kees.cook@...onical.com>
> > 
> > I've reviewed this patch briefly, Here is my personal concern...
> > 
> > On Linux, non-printable leaking is fundamental, only fixing task->comm
> > doesn't solve syslog exploit issue. Probably all /proc/kmsg user should
> > have escaping non-pritables code.
> > 
> > However, task->comm is one of most easy injection data of kernel, because
> > we have prctl(PR_SET_NAME), attacker don't need root privilege. So,
> > conservative assumption seems guard from crappy fault. Plus, this patch
> > is very small and our small TASK_COMM_LEN lead that we don't need
> > big performance concern.
> > 
> > So, I don't find demerit in this proposal. but I'm not security specialist,
> > it's only personal thinking.
> > 
> Agree. I think a escaped printk should be a more generic solution.

Is this possible? printk() doesn't know userland locale. how do it escape correctly?
When we only concern task->comm, assuming ascii-only string is enough practical.
but printk generic logic should allow non-ascii, I think.

I think userland reader process only know correct escaping way.



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