Re: [V2 PATCH] usb: mtu3: fix NULL pointer dereference

Chunfeng Yun
2020-07-02T02:53:29Z

On Wed, 2020-07-01 at 13:58 +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 30, 2020 at 03:42:22PM +0800, Chunfeng Yun wrote:
> > Some pointers are dereferenced before successful checks.
> >
> > Reported-by: Markus Elfring <Markus.Elfring@web.de>
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> > ---
> > v2: nothing changed, but abandon another patch
> > ---
> > drivers/usb/mtu3/mtu3_gadget.c | 25 ++++++++++++++++++-------
> > 1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/usb/mtu3/mtu3_gadget.c b/drivers/usb/mtu3/mtu3_gadget.c
> > index f93732e..1689ca8 100644
> > --- a/drivers/usb/mtu3/mtu3_gadget.c
> > +++ b/drivers/usb/mtu3/mtu3_gadget.c
> > @@ -332,14 +332,21 @@ static int mtu3_gadget_queue(struct usb_ep *ep,
> >
> > static int mtu3_gadget_dequeue(struct usb_ep *ep, struct usb_request *req)
> > {
> > - struct mtu3_ep *mep = to_mtu3_ep(ep);
> > - struct mtu3_request *mreq = to_mtu3_request(req);
> > + struct mtu3_ep *mep;
> > + struct mtu3_request *mreq;
> > struct mtu3_request *r;
> > + struct mtu3 *mtu;
> > unsigned long flags;
> > int ret = 0;
> > - struct mtu3 *mtu = mep->mtu;
> >
> > - if (!ep || !req || mreq->mep != mep)
> > + if (!ep || !req)
> > + return -EINVAL;
>
> How will either of those ever be NULL? The kernel will not call this
> function with either of them being NULL, right?
Yes, I find all class drivers already ensure they are not NULL.

>
> > +
> > + mep = to_mtu3_ep(ep);
> > + mtu = mep->mtu;
> > +
> > + mreq = to_mtu3_request(req);
> > + if (mreq->mep != mep)
> > return -EINVAL;
> >
> > dev_dbg(mtu->dev, "%s : req=%p\n", __func__, req);
> > @@ -373,8 +380,8 @@ static int mtu3_gadget_dequeue(struct usb_ep *ep, struct usb_request *req)
> > */
> > static int mtu3_gadget_ep_set_halt(struct usb_ep *ep, int value)
> > {
> > - struct mtu3_ep *mep = to_mtu3_ep(ep);
> > - struct mtu3 *mtu = mep->mtu;
> > + struct mtu3_ep *mep;
> > + struct mtu3 *mtu;
> > struct mtu3_request *mreq;
> > unsigned long flags;
> > int ret = 0;
> > @@ -382,6 +389,9 @@ static int mtu3_gadget_ep_set_halt(struct usb_ep *ep, int value)
> > if (!ep)
> > return -EINVAL;
>
> Same here, how can that ever happen?
Maybe when the class driver has something wrong:)

You mean it's better to remove these unnecessary checks?

Thanks

>
> >
> > + mep = to_mtu3_ep(ep);
> > + mtu = mep->mtu;
> > +
> > dev_dbg(mtu->dev, "%s : %s...", __func__, ep->name);
> >
> > spin_lock_irqsave(&mtu->lock, flags);
> > @@ -422,11 +432,12 @@ static int mtu3_gadget_ep_set_halt(struct usb_ep *ep, int value)
> > /* Sets the halt feature with the clear requests ignored */
> > static int mtu3_gadget_ep_set_wedge(struct usb_ep *ep)
> > {
> > - struct mtu3_ep *mep = to_mtu3_ep(ep);
> > + struct mtu3_ep *mep;
> >
> > if (!ep)
> > return -EINVAL;
>
> Again, same here.
>
> thanks,
>
> greg k-h