siano: make it work again with CONFIG_VMAP_STACK

commit f9c85ee6 upstream.

Reported as a Kaffeine bug:
	https://bugs.kde.org/show_bug.cgi?id=375811

The USB control messages require DMA to work. We cannot pass
a stack-allocated buffer, as it is not warranted that the
stack would be into a DMA enabled area.

On Kernel 4.9, the default is to not accept DMA on stack anymore
on x86 architecture. On other architectures, this has been a
requirement since Kernel 2.2. So, after this patch, this driver
should likely work fine on all archs.

Tested with USB ID 2040:5510: Hauppauge Windham
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
[bwh: Backported to 3.2:
 - s/sms_msg_hdr/SmsMsgHdr_ST/
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/media/dvb/siano/smsusb.c

@@ -181,11 +181,20 @@ static int smsusb_start_streaming(struct smsusb_device_t *dev)
 static int smsusb_sendrequest(void *context, void *buffer, size_t size)
 {
 	struct smsusb_device_t *dev = (struct smsusb_device_t *) context;
-	int dummy;
+	struct SmsMsgHdr_ST *phdr;
+	int dummy, ret;
 
-	smsendian_handle_message_header((struct SmsMsgHdr_ST *)buffer);
-	return usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 2),
-			    buffer, size, &dummy, 1000);
+	phdr = kmalloc(size, GFP_KERNEL);
+	if (!phdr)
+		return -ENOMEM;
+	memcpy(phdr, buffer, size);
+
+	smsendian_handle_message_header((struct SmsMsgHdr_ST *)phdr);
+	ret = usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 2),
+			    phdr, size, &dummy, 1000);
+
+	kfree(phdr);
+	return ret;
 }
 
 static char *smsusb1_fw_lkup[] = {