On Tue, Jun 04, 2024 at 10:09:43AM -0700, Nikita Zhandarovich wrote:
> Hi,
>
> On 6/4/24 07:15, Jiri Kosina wrote:
> > On Tue, 4 Jun 2024, Kees Cook wrote:
> >
> >> This isn't the right solution. The problem is that hid_class_descriptor
> >> is a flexible array but was sized as a single element fake flexible
> >> array:
> >>
> >> struct hid_descriptor {
> >> __u8 bLength;
> >> __u8 bDescriptorType;
> >> __le16 bcdHID;
> >> __u8 bCountryCode;
> >> __u8 bNumDescriptors;
> >>
> >> struct hid_class_descriptor desc[1];
> >> } __attribute__ ((packed));
> >>
> >> This likely needs to be:
> >>
> >> struct hid_class_descriptor desc[] __counted_by(bNumDescriptors);
> >>
> >> And then check for any sizeof() uses of the struct that might have changed.
> >
> > Ah, you are of course right, not sure what I was thinking. Thanks a lot
> > for catching my brainfart.
> >
> > I am dropping the patch for now; Nikita, will you please send a refreshed
> > one?
> >
>
> Thanks for catching my mistake.
>
> I'll gladly send a revised version, hoping to do it very soon.
I spent a little more time looking at this, and I'm not sure I
understand where the actual space for the descriptors comes from?
There's interface->extra that is being parsed, and effectively
hid_descriptor is being mapped into it, but it uses "sizeof(struct
hid_descriptor)" for the limit. Is more than 1 descriptor expected to
work correctly? Or is the limit being ignored? I'm a bit confused by
this code...
--
Kees Cook
