linux-kernel - Re: [PATCH][isapnp] Fix a potential NULL pointer dereference in isapnp_read

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Date:	Wed, 4 Jul 2007 03:04:13 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Jaroslav Kysela" <perex@...e.cz>
Subject: Re: [PATCH][isapnp] Fix a potential NULL pointer dereference in isapnp_read_tag()

On 03/07/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Sun, 1 Jul 2007 01:38:31 +0200
> Jesper Juhl <jesper.juhl@...il.com> wrote:
>
> > The Coverity checker spotted (as bug #809) that we dereference 'type'
> > long before we actually test it against NULL in
> > drivers/pnp/isapnp/core.c::isapnp_read_tag() - both branches of the
> > 'if (tag & 0x80)' dereference type, and since this 'if' is before the test
> > against NULL and the return of -1, this will blow up is ever type is NULL.
> > This is easy to fix by simply moving the NULL test to the beginning of
> > the function.
> >
[snip]
>
> dood, look at the callers.  NULL is not possible here.
>
You are right, there's absolutely no way that we could get a NULL
pointer there - that was sloppy of me :-(

I guess we should just get rid of the check completely.  I'll cook up
a patch for that tomorrow.

-- 
Jesper Juhl <jesper.juhl@...il.com>
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