On Thu, Oct 24, 2019 at 7:57 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 24 Oct 2019, Andrey Konovalov wrote: > > > > Is this really the sort of thing we need to catch? It isn't a bug in > > > any existing kernel code, as far as I know. Maybe only gadgetfs and > > > configfs need to worry about it. > > > > Hi Alan, > > > > Do you mean that the gadget driver must ensure that the max packet > > size in the endpoint descriptor is not zero? Do HCDs rely on that? I > > can add this check into the driver we use for USB fuzzing. > > Well, if there are any gadget drivers in the kernel which do set an > endpoint's maxpacket size to 0, they should be fixed. I'm not aware of > any. > > Of course, gadget drivers in userspace are always suspect. That's why > I suggested having gadgetfs and configfs perform this check. Even so > it's not really a _security_ risk, because only the superuser is > allowed to run a userspace gadget driver. (Although obviously it is > better to have a clean failure than to crash the system when a buggy > program runs with superuser privileges.) > > Yes, HCDs do depend on endpoints having reasonable maxpacket values. I > suppose the core should check for this. Currently we check for values > that are too large or invalid in other ways (like high-speed bulk > endpoints with maxpacket != 512), but we don't check for 0. Oh, I think I've confused the terms here. I meant to ask about UDCs. The question is whether it's OK to try and emulate a gadget with maxpacket = 0 on a board with a hardware UDC? Or can it cause issues? The fact that HCDs must ensure correct maxpacket values of course makes sense. > > In fact, that sounds like a much better solution to the problem > overall. Let's see if this patch fixes the bug... > > Alan Stern > > #syz test: https://github.com/google/kasan.git 22be26f7 > > drivers/usb/core/config.c | 5 +++++ > 1 file changed, 5 insertions(+) > > Index: usb-devel/drivers/usb/core/config.c > =================================================================== > --- usb-devel.orig/drivers/usb/core/config.c > +++ usb-devel/drivers/usb/core/config.c > @@ -348,6 +348,11 @@ static int usb_parse_endpoint(struct dev > > /* Validate the wMaxPacketSize field */ > maxp = usb_endpoint_maxp(&endpoint->desc); > + if (maxp == 0) { > + dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has wMaxPacketSize 0, skipping\n", > + cfgno, inum, asnum, d->bEndpointAddress); > + goto skip_to_next_endpoint_or_interface_descriptor; > + } > > /* Find the highest legal maxpacket size for this endpoint */ > i = 0; /* additional transactions per microframe */ >
