usb: typec: ucsi: displayport: Fix OOB altmode array index

The UCSI displayport driver indexes the connector's port altmode array
with the GET_CURRENT_CAM response after checking it is not 0xff. The
port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
not equal to 0xff, the kernel may crash with an array index OOB error.

Update the UCSI displayport driver to verify the current cam is less
than UCSI_MAX_ALTMODES before accessing the port altmode array.

Fixes: af8622f6a5 ("usb: typec: ucsi: Support for DisplayPort alt mode")
Cc: [email protected]
Signed-off-by: Jameson Thies <[email protected]>
Reviewed-by: Benson Leung <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/usb/typec/ucsi/displayport.c

@@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
 		cur = 0xff;
 	}
 
-	if (cur != 0xff) {
+	if (cur < UCSI_MAX_ALTMODES) {
 		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
 		goto err_unlock;
 	}