AZL-100199

In the Linux kernel, the following vulnerability has been resolved:

power: supply: cros_usbpd-charger: bound the EC-reported port count

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.