media: rc: validate that "rc_proto" is reasonable

Smatch complains that "rc_proto" comes from the user and it can result
in shift wrapping in ir_raw_encode_scancode()

    drivers/media/rc/rc-ir-raw.c:526 ir_raw_encode_scancode()
    error: undefined (user controlled) shift '1 << protocol'

This is true, but I reviewed the surrounding code and it appears
harmless. Anyway, let's verify that "rc_proto" is valid as a kernel
hardening measure.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/rc/lirc_dev.c

@@ -263,7 +263,8 @@ static ssize_t lirc_transmit(struct file *file, const char __user *buf,
 			goto out_unlock;
 		}
 
-		if (scan.flags || scan.keycode || scan.timestamp) {
+		if (scan.flags || scan.keycode || scan.timestamp ||
+		    scan.rc_proto > RC_PROTO_MAX) {
 			ret = -EINVAL;
 			goto out_unlock;
 		}

include/uapi/linux/lirc.h

@@ -226,6 +226,7 @@ enum rc_proto {
 	RC_PROTO_RCMM24		= 25,
 	RC_PROTO_RCMM32		= 26,
 	RC_PROTO_XBOX_DVD	= 27,
+	RC_PROTO_MAX		= RC_PROTO_XBOX_DVD,
 };
 
 #endif