Re: [PATCH 2/4] virtio_input: validate device-reported multitouch slot count

On Wed, Jul 15, 2026 at 5:50 PM Michael S. Tsirkin <[email protected]> wrote:
>
> On Wed, Jul 15, 2026 at 04:22:41PM +0200, Hari Mishal wrote:
> > nslots is derived from the ABS_MT_SLOT maximum reported by the
> > virtio device. A device could report a bogus maximum (e.g. -1)
> > making nslots = 0, which input_mt_init_slots() does not reject;
> > it returns success without allocating any slot storage, silently
> > leaving the device registered as multitouch capable with no
> > backing state.
>
> So let's disable multitouch instead?
>

So rather than failing the whole probe, just warn and clear
ABS_MT_SLOT from absbit in that case, so the rest of the device
still registers? I took my lead from input_mt_init_slots(), which
has its own internal cap and returns -EINVAL when the device
reports more than 1024 slots.
Shall I modify that case to get the same "warn and disable
multitouch" for consistency, or is a hard failure better there since
it's a different type of bad device data?
Happy to fix it either way! Just want to confirm before sending V2.

Cheers,
Hari