linux-kernel - Re: [PATCH 4.19 57/72] usb: usb251xb: fix to avoid potential NULL pointer dereference

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Date:   Sat, 4 May 2019 08:45:27 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Aditya Pakki <pakki001@....edu>,
        Richard Leitner <richard.leitner@...data.com>,
        "Sasha Levin (Microsoft)" <sashal@...nel.org>
Subject: Re: [PATCH 4.19 57/72] usb: usb251xb: fix to avoid potential NULL
 pointer dereference

On Fri, May 03, 2019 at 11:32:35PM +0200, Pavel Machek wrote:
> On Thu 2019-05-02 17:21:19, Greg Kroah-Hartman wrote:
> > [ Upstream commit 41f00e6e9e55546390031996b773e7f3c1d95928 ]
> > 
> > of_match_device in usb251xb_probe can fail and returns a NULL pointer.
> > The patch avoids a potential NULL pointer dereference in this scenario.
> > 
> > Signed-off-by: Aditya Pakki <pakki001@....edu>
> > Reviewed-by: Richard Leitner <richard.leitner@...data.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Signed-off-by: Sasha Levin (Microsoft) <sashal@...nel.org>
> > ---
> >  drivers/usb/misc/usb251xb.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
> > index a6efb9a72939..5f7734c729b1 100644
> > --- a/drivers/usb/misc/usb251xb.c
> > +++ b/drivers/usb/misc/usb251xb.c
> > @@ -601,7 +601,7 @@ static int usb251xb_probe(struct usb251xb *hub)
> >  							   dev);
> >  	int err;
> >  
> > -	if (np) {
> > +	if (np && of_id) {
> >  		err = usb251xb_get_ofdata(hub,
> >  					  (struct usb251xb_data *)of_id->data);
> >  		if (err) {
> 
> Are you sure this si correct?
> 
> If of_id is NULL, this will proceed without setting up hub->conf_data
> etc.
> 
> I'd expect it to just return error from probe...?

I think it will error out later on.

> Was this tested?

Don't know, error paths are hard to test :)

But the code obviously fixes a null dereference, so that's a good thing.

thanks,

greg k-h