HID: Fix assumption that devices have inputs

HID: Fix assumption that devices have inputs

commit d9d4b1e46d9543a82c23f6df03f4ad697dab361b upstream.

The syzbot fuzzer found a slab-out-of-bounds write bug in the hid-gaff
driver.  The problem is caused by the driver's assumption that the
device must have an input report.  While this will be true for all
normal HID input devices, a suitably malicious device can violate the
assumption.

The same assumption is present in over a dozen other HID drivers.
This patch fixes them by checking that the list of hid_inputs for the
hid_device is nonempty before allowing it to be used.

Reported-and-tested-by: syzbot+403741a091bf41d4ae79@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
[bwh: Backported to 3.16:
 - Drop changes in hid-logitech-hidpp, hid-microsoft
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>