Re: [PATCH v2] usb: gadget: core: Check for unset descriptor

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Jul 25, 2024 at 02:23:25PM -0400, Alan Stern wrote:
> On Thu, Jul 25, 2024 at 06:56:19AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jul 24, 2024 at 09:04:20PM -0400, crwulff@gmail.com wrote:
> > > From: Chris Wulff <crwulff@gmail.com>
> > > 
> > > Make sure the descriptor has been set before looking at maxpacket.
> > > This fixes a null pointer panic in this case.
> > > 
> > > This may happen if the gadget doesn't properly set up the endpoint
> > > for the current speed, or the gadget descriptors are malformed and
> > > the descriptor for the speed/endpoint are not found.
> > > 
> > > No current gadget driver is known to have this problem, but this
> > > may cause a hard-to-find bug during development of new gadgets.
> > > 
> > > Fixes: 54f83b8c8ea9 ("USB: gadget: Reject endpoints with 0 maxpacket value")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Chris Wulff <crwulff@gmail.com>
> > > ---
> > > v2: Added WARN_ONCE message & clarification on causes
> > > v1: https://lore.kernel.org/all/20240721192048.3530097-2-crwulff@gmail.com/
> > > ---
> > >  drivers/usb/gadget/udc/core.c | 10 ++++------
> > >  1 file changed, 4 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> > > index 2dfae7a17b3f..81f9140f3681 100644
> > > --- a/drivers/usb/gadget/udc/core.c
> > > +++ b/drivers/usb/gadget/udc/core.c
> > > @@ -118,12 +118,10 @@ int usb_ep_enable(struct usb_ep *ep)
> > >  		goto out;
> > >  
> > >  	/* UDC drivers can't handle endpoints with maxpacket size 0 */
> > > -	if (usb_endpoint_maxp(ep->desc) == 0) {
> > > -		/*
> > > -		 * We should log an error message here, but we can't call
> > > -		 * dev_err() because there's no way to find the gadget
> > > -		 * given only ep.
> > > -		 */
> > > +	if (!ep->desc || usb_endpoint_maxp(ep->desc) == 0) {
> > > +		WARN_ONCE(1, "%s: ep%d (%s) has %s\n", __func__, ep->address, ep->name,
> > > +			  (!ep->desc) ? "NULL descriptor" : "maxpacket 0");
> > 
> > So you just rebooted a machine that hit this, that's not good at all.
> > Please log the error and recover, don't crash a system (remember,
> > panic-on-warn is enabled in billions of Linux systems.)
> 
> That should not be a problem.  This WARN_ONCE is expected never to be 
> triggered except by a buggy gadget driver.  It's a debugging tool; the 
> developer will get an indication in the kernel log of where the problem 
> is instead of just a panic.

Ok, if this can never be hit by a user action, then it's ok to leave
as-is, it wasn't obvious to me that this is the case, sorry.  I'll
queue this up after -rc1 is out.

thanks,

greg k-h