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

[Bryam Vargas via B4 Relay]

From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

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@xxxxxxxxxxxxxxx
Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
---
 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);
 
 	x_max = get_unaligned_le16(&ts->config[RESOLUTION_LOC]);
 	y_max = get_unaligned_le16(&ts->config[RESOLUTION_LOC + 2]);

---
base-commit: 8e65320d91cdc3b241d4b94855c88459b91abf66
change-id: 20260612-b4-disp-6844625d-463f81173dc6

Best regards,
-- 
Bryam Vargas <hexlabsecurity@xxxxxxxxx>