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

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Date:	Thu, 19 Jul 2007 18:29:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
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

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.
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