i2c: cp2615: fix serial string NULL-deref at probe

The cp2615 driver uses the USB device serial string as the i2c adapter
name but does not make sure that the string exists.

Verify that the device has a serial number before accessing it to avoid
triggering a NULL-pointer dereference (e.g. with malicious devices).

Fixes: 4a76954 ("i2c: cp2615: add i2c driver for Silicon Labs' CP2615 Digital Audio Bridge")
Cc: [email protected]	# 5.13
Cc: Bence Csókás <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
Reviewed-by: Bence Csókás <[email protected]>
Signed-off-by: Andi Shyti <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: jhovold

drivers/i2c/busses/i2c-cp2615.c

@@ -298,6 +298,9 @@ cp2615_i2c_probe(struct usb_interface *usbif, const struct usb_device_id *id)
 	if (!adap)
 		return -ENOMEM;
 
+	if (!usbdev->serial)
+		return -EINVAL;
+
 	strscpy(adap->name, usbdev->serial, sizeof(adap->name));
 	adap->owner = THIS_MODULE;
 	adap->dev.parent = &usbif->dev;