Re: [PATCH] usb: gadget: Check for NULL pointer in disconnect

[Badhri Jagan Sridharan]

> Do you really see some udc drivers call it after composite_unbind is
> called? If it is, you may add dump_stack() to track that error.
>
> Besides this, function suspended_show is needed to add cdev NULL pointer
> checking.

We see this happening occasionally in *not yet* upstreamed UDC
code of some vendors (Yes, disconnect being called after unbind)
After reviewing the entire composite.c file, I did notice that
none of the functions check for NULL pointer when cdev is
obtained from get_gadget_data.
Is crashing/bringing down the whole kernel intentionally
left to happen ? Isn't printing a WARN/ERROR msg and
returning not the preferable approach ?

On 03/22/2015 12:43 AM, Peter Chen wrote:
> On Fri, Mar 20, 2015 at 04:40:52PM -0700, Badhri Jagan Sridharan wrote:
> > Added a safety net to make sure that
> > composite_disconnect does not end up disconneting
> > a NULL device. Prevents NULL pointer crash.
> >
> > Signed-off-by: Badhri Jagan Sridharan <Badhri@xxxxxxxxxx>
> > ---
> >   drivers/usb/gadget/composite.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> > index 13adfd1..90b37bd 100644
> > --- a/drivers/usb/gadget/composite.c
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -1823,6 +1823,11 @@ void composite_disconnect(struct usb_gadget *gadget)
> >   	struct usb_composite_dev	*cdev = get_gadget_data(gadget);
> >   	unsigned long			flags;
> >
> > +	if (!cdev) {
> > +		WARN(1, "Trying to disconnect a NULL composite device\n");
> > +		return;
> > +	}
> > +
>
> Do you really see some udc drivers call it after composite_unbind is
> called? If it is, you may add dump_stack() to track that error.
>
> Besides this, function suspended_show is needed to add cdev NULL pointer
> checking.
>
> >   	/* REVISIT:  should we have config and device level
> >   	 * disconnect callbacks?
> >   	 */
> > --
> > 2.2.0.rc0.207.ga3a616c
> >
> > --
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