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

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Date:	Fri, 25 Jun 2010 08:56:28 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	kosaki.motohiro@...fujitsu.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>,
	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

> 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.



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