linux-kernel - Re: [PATCH 5/5] staging/otus: Move a dereference below a NULL test

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Date:	Sat, 11 Jul 2009 13:58:05 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>, gregkh@...e.de,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 5/5] staging/otus: Move a dereference below a NULL test

On Sat, 11 Jul 2009, Julia Lawall wrote:

> On Sat, 11 Jul 2009, Jiri Slaby wrote:
> 
> > On 07/11/2009 12:17 PM, Jaswinder Singh Rajput wrote:
> > > On Sat, 2009-07-11 at 10:17 +0200, Jiri Slaby wrote:
> > >> On 07/11/2009 09:51 AM, Julia Lawall wrote:
> > >>> --- a/drivers/staging/otus/wwrap.c
> > >>> +++ b/drivers/staging/otus/wwrap.c
> > >>> @@ -1016,12 +1016,13 @@ void kevent(struct work_struct *work)
> > >>>  {
> > >>>      struct usbdrv_private *macp =
> > >>>                 container_of(work, struct usbdrv_private, kevent);
> > >>> -    zdev_t *dev = macp->device;
> > >>> +    zdev_t *dev;
> > >>>  
> > >>>      if (macp == NULL)
> > >>>      {
> > >>>          return;
> > >>>      }
> > >>
> > >> The test is rather useless here.
> > >>
> > > 
> > > Why useless, it should be non-null before setting to dev.
> > 
> > Even if work was NULL, macp won't be NULL.
> 
> work could be a small negative number such that calling container_of would 
> return 0.

On the other hand, that does not seem to be possible in this case, since 
work is passed through INIT_WORK, which dereferences the work value.

julia
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