Subject: Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes
From: Stefani Seibold <stefani@seibold.net>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Kees Cook <kees.cook@canonical.com>, linux-kernel@vger.kernel.org,
       Greg Kroah-Hartman <gregkh@suse.de>,
       Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
       Veaceslav Falico <vfalico@redhat.com>,
       Alexander Viro <viro@zeniv.linux.org.uk>,
       Oleg Nesterov <oleg@redhat.com>, Neil Horman <nhorman@tuxdriver.com>,
       Roland McGrath <roland@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
       Thomas Gleixner <tglx@linutronix.de>, Eric Paris <eparis@redhat.com>,
       James Morris <jmorris@namei.org>,
       "Andrew G. Morgan" <morgan@kernel.org>,
       Dhaval Giani <dhaval.giani@gmail.com>,
       "Serge E. Hallyn" <serue@us.ibm.com>, Steve Grubb <sgrubb@redhat.com>,
       Christoph Hellwig <hch@lst.de>, linux-fsdevel@vger.kernel.org
In-Reply-To: <20100625082722.8031.A69D9226@jp.fujitsu.com>
References: <20100624190527.GD5917@outflux.net>
	 <20100625082722.8031.A69D9226@jp.fujitsu.com>
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Date: Mon, 28 Jun 2010 19:48:38 +0200
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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@canonical.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.

Stefani


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