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 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 + 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.
