linux-kernel - Re: [PATCH] usb: musb: Fix potential NULL dereference

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Date:   Fri, 25 Jan 2019 16:37:48 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Bin Liu <b-liu@...com>
cc:     "Matwey V. Kornilov" <matwey.kornilov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:MUSB MULTIPOINT HIGH SPEED DUAL-ROLE CONTROLLER" 
        <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: musb: Fix potential NULL dereference

On Fri, 25 Jan 2019, Bin Liu wrote:

> On Thu, Jan 24, 2019 at 09:47:02PM +0300, Matwey V. Kornilov wrote:
> > By the way, why do we need to store the qh in urb->hcpriv?
> > qh can always be accessible through urb->ep->hcpriv
> > Wouldn't it be better to drop entire urb->hcpriv usage?
> 
> I am not sure why. The code is there since the first commit in a decade
> ago. But I tend to agree with you.
> 
> In a quick search for urb->hcpriv and urb->ep->hcpriv, based on the
> usage in core/hcd.c, it seems to me that urb->hcpriv should not be
> changed in each controller driver, but I see both have been used in most
> controller drivers. I will leave this to others to educate me.

In some of the older HCDs, urb->hcpriv != NULL is used to indicate that 
urb is on an endpoint queue.  Perhaps that usage was copied.

Alan Stern