[PATCH synaptics] Reset num_active_touches on DeviceOff (#52496)

[Chase Douglas]

On 08/29/2012 11:54 PM, Peter Hutterer wrote:
> When disabling the device, reset num_active_touches to zero. Otherwise,
> num_active_touches stays at the value it was on DeviceOff(). Future touches
> add to that value until the index may go past priv->open_slots[].
> That causes spurious memory corruption on touch ends.
>
> And as of 55fc42e7c9b4948cadd4f98ef7b6a3b12e268e3e we ignore pre-existing
> touches anyway.
>
> Test-case:
> - place num_touches fingers on the touchpad
> - xinput disable <device>
> - lift fingers
> - xinput enable <device>
> - place finger on device, num_active_touches is now (num_touches + 1)
>
> X.Org Bug 52496 <http://bugs.freedesktop.org/show_bug.cgi?id=52496>
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> ---
>   src/synaptics.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/src/synaptics.c b/src/synaptics.c
> index 27a37d7..0472197 100644
> --- a/src/synaptics.c
> +++ b/src/synaptics.c
> @@ -977,6 +977,7 @@ SynapticsReset(SynapticsPrivate * priv)
>       priv->lastButtons = 0;
>       priv->prev_z = 0;
>       priv->prevFingers = 0;
> +    priv->num_active_touches = 0;
>       memset(priv->open_slots, 0, priv->num_slots * sizeof(int));
>   }
>
> @@ -2611,6 +2612,7 @@ UpdateTouchState(InputInfoPtr pInfo, struct SynapticsHwState *hw)
>           if (hw->slot_state[i] == SLOTSTATE_OPEN) {
>               priv->open_slots[priv->num_active_touches] = i;
>               priv->num_active_touches++;
> +            BUG_WARN(priv->num_active_touches > priv->num_slots);
>           }
>           else if (hw->slot_state[i] == SLOTSTATE_CLOSE) {
>               Bool found = FALSE;
>

Ugh, I thought we caught all of these...

Reviewed-by: Chase Douglas <chase.douglas at canonical.com>