Re: [syzbot] WARNING in hid_submit_ctrl/usb_submit_urb

On Fri, 20 Aug 2021, Alan Stern wrote:

quoted

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

That's good to know.  Still, I suspect there's a better way of handling 
this condition.

In particular, does it make sense to accept descriptors for input or 
feature reports with length zero?  I can't imagine what good such 
reports would do.

I quickly went through drivers + some hidraw users, and can't spot any use 
case for it.

On the other hand, I'm not familiar enough with the code to know the 
right way to reject these descriptors and reports.  It looks like the 
HID subsystem was not designed with this sort of check in mind.

Benjamin and Jiri, what do you think?  Is it okay to allow descriptors 
for zero-length reports and just pretend they have length 1 (as the 
patch tested by syzbot did), or should we instead reject them during 
probing?

I think it's a good band-aid for 5.14 (or 5.14-stable if we don't make 
it), and if it turns out to break something (which I don't expect), than 
we can look into rejecting already during probe.

Benjamin, is there a way to run this quickly through your HID regression 
testing machinery?

Thanks,

-- 
Jiri Kosina
SUSE Labs