linux-kernel - Re: [PATCH] USB Pegasus driver - avoid a potential NULL pointer dereference.

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Message-ID: <9a8748490707281655u66e50bbfqba58687b579a85fe@mail.gmail.com>
Date:	Sun, 29 Jul 2007 01:55:00 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Satyam Sharma" <satyam.sharma@...il.com>
Cc:	"Petko Manolov" <petkan@...rs.sourceforge.net>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <greg@...ah.com>,
	linux-usb-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH] USB Pegasus driver - avoid a potential NULL pointer dereference.

On 29/07/07, Satyam Sharma <satyam.sharma@...il.com> wrote:
> Hi,
>
> On 7/29/07, Jesper Juhl <jesper.juhl@...il.com> wrote:
> > Hello,
> >
> > This patch makes sure we don't dereference a NULL pointer in
> > drivers/net/usb/pegasus.c::write_bulk_callback() in the initial
> > struct net_device *net = pegasus->net; assignment.
> > The existing code checks if 'pegasus' is NULL and bails out if
> > it is, so we better not touch that pointer until after that check.
> > [...]
> > diff --git a/drivers/net/usb/pegasus.c b/drivers/net/usb/pegasus.c
> > index a05fd97..04cba6b 100644
> > --- a/drivers/net/usb/pegasus.c
> > +++ b/drivers/net/usb/pegasus.c
> > @@ -768,11 +768,13 @@ done:
> >  static void write_bulk_callback(struct urb *urb)
> >  {
> >         pegasus_t *pegasus = urb->context;
> > -       struct net_device *net = pegasus->net;
> > +       struct net_device *net;
> >
> >         if (!pegasus)
> >                 return;
> >
> > +       net = pegasus->net;
> > +
> >         if (!netif_device_present(net) || !netif_running(net))
> >                 return;
>
> Is it really possible that we're called into this function with
> urb->context == NULL? If not, I'd suggest let's just get rid of
> the check itself, instead.
>
I'm not sure. I am not very familiar with this code. I just figured
that moving the assignment is potentially a little safer and it is
certainly no worse than the current code, so that's a safe and
potentially benneficial change. Removing the check may be safe but I'm
not certain enough to make that call...

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