Re: [PATCH] power: supply: cros_usbpd-charger: bound the EC-reported port count

On Mon, Jun 15, 2026 at 04:04:07AM -0500, Bryam Vargas via B4 Relay wrote:
> From: Bryam Vargas <[email protected]>
> 
> cros_usbpd_charger_probe() reads two port counts from the EC and uses
> one of them, num_charger_ports, as the loop bound when populating a
> fixed-size array:
> 
> 	struct port_data *ports[EC_USB_PD_MAX_PORTS];	/* 8 entries */
> 	...
> 	for (i = 0; i < charger->num_charger_ports; i++)
> 		charger->ports[charger->num_registered_psy++] = port;
> 
> Both num_usbpd_ports (from EC_CMD_USB_PD_PORTS) and num_charger_ports
> (from EC_CMD_CHARGE_PORT_COUNT) are u8 values reported by the EC. The
> only validation is a sanity check that compares the two EC-reported
> values against each other:
> 
> 	if (num_charger_ports < num_usbpd_ports ||
> 	    num_charger_ports > num_usbpd_ports + 1)
> 		return -EPROTO;
> 
> It never checks either count against EC_USB_PD_MAX_PORTS, the size of
> the ports[] array. A malfunctioning, malicious or compromised EC that
> reports num_usbpd_ports == num_charger_ports == N for any N > 8 (for
> example both 255) passes this check, and the loop then writes N pointers
> into the 8-entry ports[] array embedded in the devm_kzalloc()'d
> charger_data, overflowing it by up to 255 - 8 = 247 entries (~1976
> bytes): a slab out-of-bounds write.
> 
> Reject a port count larger than the ports[] array can hold.
> 
> Fixes: f68b883e8fad ("power: supply: add cros-ec USBPD charger driver.")
> Cc: [email protected]
> Signed-off-by: Bryam Vargas <[email protected]>

With or without the minor comment:
Reviewed-by: Tzung-Bi Shih <[email protected]>

> diff --git a/drivers/power/supply/cros_usbpd-charger.c b/drivers/power/supply/cros_usbpd-charger.c
> index 7d3e676a951c..d639957f9775 100644
> --- a/drivers/power/supply/cros_usbpd-charger.c
> +++ b/drivers/power/supply/cros_usbpd-charger.c
> @@ -589,10 +589,12 @@ static int cros_usbpd_charger_probe(struct platform_device *pd)
>  
>  	/*
>  	 * Sanity checks on the number of ports:
> -	 *  there should be at most 1 dedicated port
> +	 *  there should be at most 1 dedicated port, and the count is
> +	 *  reported by the EC, so it must not exceed the ports[] array.
>  	 */

Nit: The mention of EC is redundant.  I'd suggest:

"...must not exceed the maximum number of supported ports
 (EC_USB_PD_MAX_PORTS)"