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

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Date:	Fri, 13 Nov 2009 22:26:20 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	Valdis.Kletnieks@...edu
Cc:	Casey Schaufler <casey@...aufler-ca.com>,
	James Morris <jmorris@...ei.org>,
	"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 Fri, 13 Nov 2009, Valdis.Kletnieks@...edu wrote:

> On Thu, 12 Nov 2009 18:11:55 PST, Casey Schaufler said:
> > James Morris wrote:
> > > Do you see potential for a buffer overrun in this case?
> 
> > No, but I hate arguing with people who think that every time
> > they see strcmp that they have found a security flaw.
> 
> How do you feel about people who think every time they see strcmp()
> "Oh crap, something that needs auditing"? ;)
> 
> The biggest problem with strcmp() is that even if it got audited when that code
> went in, it's prone to unaudited breakage when somebody changes something in
> some other piece of code, quite often in some other .c file in some other
> directory.
> 
> Julia, is there a way to use coccinelle to detect unsafe changes like that?  Or
> is expressing those semantics too difficult?

Could you give a concrete example of something that would be a problem?
If something like alias analysis is required, to know what strings a 
variable might be bound to, that might be difficult.  Coccinelle works 
better when there is some concrete codeto match against.  But it is 
possible to eg match functions that have a certain property of their 
return value, or to collect all of the values that are stored in a 
structure field.

julia
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