linux-kernel - Re: [PATCH 3/4] security/selinux: decrement sizeof size in strncmp

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Message-ID: <alpine.LRH.2.00.0911130833220.5497@tundra.namei.org>
Date:	Fri, 13 Nov 2009 08:41:26 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Casey Schaufler <casey@...aufler-ca.com>
cc:	Julia Lawall <julia@...u.dk>, "Serge E. Hallyn" <serue@...ibm.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/4] security/selinux: decrement sizeof size in strncmp

On Thu, 12 Nov 2009, Casey Schaufler wrote:

> I strongly suggest that this is not what is wanted.
>     strcmp(x,y)
> and
>     strncmp(x,y,sizeof(y))
> 
> are functionally equivalent and strcmp has a bad reputation in
> the security community because it is associated with potential
> buffer overrun issues.

Do you see potential for a buffer overrun in this case?

The strings being compared are "sysfs" and the name field of 'struct 
file_system_type'.  The kernel code elsewhere assumes the latter string to 
be a valid zero-terminated string, and we should, too.


- James
-- 
James Morris
<jmorris@...ei.org>
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