linux-kernel - Re: [PATCH] Fix a use after free bug in kernel->userspace relay file support

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Message-ID: <20070720014236.GA5836@Krystal>
Date:	Thu, 19 Jul 2007 21:42:36 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Paul Mundt <lethal@...ux-sh.org>,
	Tom Zanussi <zanussi@...ibm.com>,
	Karim Yaghmour <karim@...rsys.com>,
	Jesper Juhl <jesper.juhl@...il.com>,
	"David J. Wilder" <wilder@...ibm.com>
Subject: Re: [PATCH] Fix a use after free bug in kernel->userspace relay file support

* Andrew Morton (akpm@...ux-foundation.org) wrote:
> On Thu, 19 Jul 2007 21:09:09 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > Coverity spotted what looks like a real possible case of using a 
> > variable after it has been freed.
> > The problem is in kernel/relay.c::relay_open_buf()
> > 
> > If the code hits "goto free_buf;" it ends up in this code :
> > 
> >   free_buf:
> >     	relay_destroy_buf(buf);	<--- calls kfree() on 'buf'.
> >   free_name:
> >    	kfree(tmpname);
> >   end:
> >   	return buf;		<-- use after free of 'buf'.
> > 
> > I read through the callers and they all handle a NULL return 
> > from this function as an error (and hitting the 'free_buf' label 
> > only happens on failure to chan->cb->create_buf_file(), so that 
> > looks like a clear error to me). 
> > 
> > The patch simply sets 'buf' to NULL after the call to 
> > relay_destroy_buf(buf); - as far as I can see that should take 
> > care of the problem.
> > 
> > The patch also corrects a reference to a documentation file while 
> > I was at it.
> > 
> > Note from Mathieu: the documentation reference change should have been
> > done in a separate patch, but I guess no one will really care.
> > 
> > Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
> > Acked-by: "David J. Wilder" <wilder@...ibm.com>
> > Tested-by: "David J. Wilder" <wilder@...ibm.com>
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> 
> I'm going to infer from all this that the patch was actually written
> by Jesper.  Correct?
> 
> If so, it shuld have had From: Jesper Juhl <jesper.juhl@...il.com>
> right at the start of the changelog.

Yes, it's the case. Thanks.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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