Re: [PATCH v2] HID: core: Sanitize event code and type when mapping input

On Thu, Aug 27, 2020 at 11:33 AM Jiri Kosina [off-list ref] wrote:

On Wed, 26 Aug 2020, Marc Zyngier wrote:

quoted

When calling into hid_map_usage(), the passed event code is
blindly stored as is, even if it doesn't fit in the associated bitmap.

This event code can come from a variety of sources, including devices
masquerading as input devices, only a bit more "programmable".

Instead of taking the event code at face value, check that it actually
fits the corresponding bitmap, and if it doesn't:
- spit out a warning so that we know which device is acting up
- NULLify the bitmap pointer so that we catch unexpected uses

Code paths that can make use of untrusted inputs can now check
that the mapping was indeed correct and bail out if not.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
* From v1:
  - Dropped the input.c changes, and turned hid_map_usage() into
    the validation primitive.
  - Handle mapping failures in hidinput_configure_usage() and
    mt_touch_input_mapping() (on top of hid_map_usage_clear() which
    was already handled)

Benjamin, could you please run this through your regression testing
machinery?

It's a non-trivial core change, at the same time I'd like not to postpone
it for 5.10 due to its nature.

OK, just passed the v4 to the testsuite, and this seems good. It won't
break touchscreens nor keyboards/mice that needed to be added in the
past.

So this is a go for me.

Cheers,
Benjamin

Thanks,

--
Jiri Kosina
SUSE Labs