Re: [PATCH] usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

[Jia-Ju Bai]

Thanks for the reply :)

On 2023/9/25 17:38, Greg KH wrote:
> On Mon, Sep 25, 2023 at 05:17:41PM +0800, Jia-Ju Bai wrote:
> > In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without
> > holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
> >
> >      spin_lock_irqsave(&hsotg->lock, flags);
> >      ...
> > 	if (!urb->hcpriv) {
> > 		dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n");
> > 		goto out;
> > 	}
> >      rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
> >      ...
> > out:
> >      spin_unlock_irqrestore(&hsotg->lock, flags);
> >
> > When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are
> > concurrently executed, the NULL check of "urb->hcpriv" can be executed
> > before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used
> > in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL
> > pointer dereference.
> Odd trailing spaces in your changelog text, is that intentional?

They are caused by the configuration of my file editor, and I changed it 
just now.

> > To fix this possible bug, "urb->hcpriv = NULL" should be executed with
> > holding the lock "hsotg->lock".
> >
> > Signed-off-by: Jia-Ju Bai <baijiaju@xxxxxxxxxxx>
> > ---
> >   drivers/usb/dwc2/hcd.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
> > index 657f1f659ffa..35c7a4df8e71 100644
> > --- a/drivers/usb/dwc2/hcd.c
> > +++ b/drivers/usb/dwc2/hcd.c
> > @@ -4769,8 +4769,8 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
> >   	if (qh_allocated && qh->channel && qh->channel->qh == qh)
> >   		qh->channel->qh = NULL;
> >   fail2:
> > -	spin_unlock_irqrestore(&hsotg->lock, flags);
> >   	urb->hcpriv = NULL;
> > +	spin_unlock_irqrestore(&hsotg->lock, flags);
> >   	kfree(qtd);
> >   fail1:
> >   	if (qh_allocated) {
> > --
> > 2.34.1
> What commit id does this fix?
>
> And how did you test this to verify it works properly?
>
> And how was it found?

I sent a v2 patch to add these details and fix the mistakes about 
trailing spaces.


Thanks,
Jia-Ju Bai