Re: [PATCH] Input: goodix - clamp the device-reported contact count

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Sun, Jun 14, 2026 at 01:44:07PM +0200, Hans de Goede wrote:
> Hi,
> 
> On 13-Jun-26 04:10, Bryam Vargas via B4 Relay wrote:
> > From: Bryam Vargas <hexlabsecurity@proton.me>
> > 
> > goodix_ts_read_input_report() copies the number of touch points reported
> > by the device into an on-stack buffer
> > 
> > 	u8 point_data[2 + GOODIX_MAX_CONTACT_SIZE * GOODIX_MAX_CONTACTS];
> > 
> > which is sized for at most GOODIX_MAX_CONTACTS (10) contacts. The only
> > runtime check bounds the per-interrupt count against ts->max_touch_num,
> > but that value is taken verbatim from a 4-bit field of the device
> > configuration block and is never clamped:
> > 
> > 	ts->max_touch_num = ts->config[MAX_CONTACTS_LOC] & 0x0f;
> > 
> > The nibble can be 0..15, so a malfunctioning, malicious or counterfeit
> > controller (or an attacker tampering with the I2C bus) can advertise up
> > to 15 contacts. goodix_ts_read_input_report() then accepts a touch_num
> > of up to 15 and the second goodix_i2c_read() writes
> > ts->contact_size * (touch_num - 1) bytes past the one-contact header into
> > point_data - up to 30 bytes (45 with the 9-byte report format) beyond the
> > 92-byte buffer: a stack out-of-bounds write.
> > 
> > Clamp max_touch_num to GOODIX_MAX_CONTACTS, the number of contacts
> > point_data[] is sized for, when reading it from the configuration.
> > 
> > Fixes: a7ac7c95d468 ("Input: goodix - use max touch number from device config")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
> 
> Thanks, patch looks good to me:
> 
> Reviewed-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
> 
> Regards,
> 
> Hans
> 
> 
> > ---
> >  drivers/input/touchscreen/goodix.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
> > index f8798d11ec03..17fcfe45988c 100644
> > --- a/drivers/input/touchscreen/goodix.c
> > +++ b/drivers/input/touchscreen/goodix.c
> > @@ -1057,7 +1057,8 @@ static void goodix_read_config(struct goodix_ts_data *ts)
> >  	}
> >  
> >  	ts->int_trigger_type = ts->config[TRIGGER_LOC] & 0x03;
> > -	ts->max_touch_num = ts->config[MAX_CONTACTS_LOC] & 0x0f;
> > +	ts->max_touch_num = min(ts->config[MAX_CONTACTS_LOC] & 0x0f,
> > +				GOODIX_MAX_CONTACTS);

Should we drop the report if is has bogus data in it?

Thanks.

-- 
Dmitry