usbnet: ipheth: add CDC NCM support

Recent iOS releases support CDC NCM encapsulation on RX. This mode is
the default on macOS and Windows. In this mode, an iOS device may include
one or more Ethernet frames inside a single URB.

Freshly booted iOS devices start in legacy mode, but are put into
NCM mode by the official Apple driver. When reconnecting such a device
from a macOS/Windows machine to a Linux host, the device stays in
NCM mode, making it unusable with the legacy ipheth driver code.

To correctly support such a device, the driver has to either support
the NCM mode too, or put the device back into legacy mode.

To match the behaviour of the macOS/Windows driver, and since there
is no documented control command to revert to legacy mode, implement
NCM support. The device is attempted to be put into NCM mode by default,
and falls back to legacy mode if the attempt fails.

Signed-off-by: Foster Snowhill <[e-mail]>
Tested-by: Georgi Valkov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/usb/ipheth.c

···
 #include <linux/ethtool.h>
 #include <linux/usb.h>
 #include <linux/workqueue.h>
+#include <linux/usb/cdc.h>
 
 #define USB_VENDOR_APPLE        0x05ac
 
···
 #define IPHETH_USBINTF_SUBCLASS 253
 #define IPHETH_USBINTF_PROTO    1
 
-#define IPHETH_BUF_SIZE         1514
 #define IPHETH_IP_ALIGN		2	/* padding at front of URB */
+#define IPHETH_NCM_HEADER_SIZE  (12 + 96) /* NCMH + NCM0 */
+#define IPHETH_TX_BUF_SIZE      ETH_FRAME_LEN
+#define IPHETH_RX_BUF_SIZE_LEGACY (IPHETH_IP_ALIGN + ETH_FRAME_LEN)
+#define IPHETH_RX_BUF_SIZE_NCM	65536
+
 #define IPHETH_TX_TIMEOUT       (5 * HZ)
 
 #define IPHETH_INTFNUM          2
···
 #define IPHETH_CTRL_TIMEOUT     (5 * HZ)
 
 #define IPHETH_CMD_GET_MACADDR   0x00
+#define IPHETH_CMD_ENABLE_NCM    0x04
 #define IPHETH_CMD_CARRIER_CHECK 0x45
 
 #define IPHETH_CARRIER_CHECK_TIMEOUT round_jiffies_relative(1 * HZ)
···
 	u8 bulk_out;
 	struct delayed_work carrier_work;
 	bool confirmed_pairing;
+	int (*rcvbulk_callback)(struct urb *urb);
+	size_t rx_buf_len;
 };
 
 static int ipheth_rx_submit(struct ipheth_device *dev, gfp_t mem_flags);
···
 	if (rx_urb == NULL)
 		goto free_tx_urb;
 
-	tx_buf = usb_alloc_coherent(iphone->udev, IPHETH_BUF_SIZE,
+	tx_buf = usb_alloc_coherent(iphone->udev, IPHETH_TX_BUF_SIZE,
 				    GFP_KERNEL, &tx_urb->transfer_dma);
 	if (tx_buf == NULL)
 		goto free_rx_urb;
 
-	rx_buf = usb_alloc_coherent(iphone->udev, IPHETH_BUF_SIZE + IPHETH_IP_ALIGN,
+	rx_buf = usb_alloc_coherent(iphone->udev, iphone->rx_buf_len,
 				    GFP_KERNEL, &rx_urb->transfer_dma);
 	if (rx_buf == NULL)
 		goto free_tx_buf;
···
 	return 0;
 
 free_tx_buf:
-	usb_free_coherent(iphone->udev, IPHETH_BUF_SIZE, tx_buf,
+	usb_free_coherent(iphone->udev, IPHETH_TX_BUF_SIZE, tx_buf,
 			  tx_urb->transfer_dma);
 free_rx_urb:
 	usb_free_urb(rx_urb);
···
 
 static void ipheth_free_urbs(struct ipheth_device *iphone)
 {
-	usb_free_coherent(iphone->udev, IPHETH_BUF_SIZE + IPHETH_IP_ALIGN, iphone->rx_buf,
+	usb_free_coherent(iphone->udev, iphone->rx_buf_len, iphone->rx_buf,
 			  iphone->rx_urb->transfer_dma);
-	usb_free_coherent(iphone->udev, IPHETH_BUF_SIZE, iphone->tx_buf,
+	usb_free_coherent(iphone->udev, IPHETH_TX_BUF_SIZE, iphone->tx_buf,
 			  iphone->tx_urb->transfer_dma);
 	usb_free_urb(iphone->rx_urb);
 	usb_free_urb(iphone->tx_urb);
···
 	usb_kill_urb(dev->rx_urb);
 }
 
+static int ipheth_consume_skb(char *buf, int len, struct ipheth_device *dev)
+{
+	struct sk_buff *skb;
+
+	skb = dev_alloc_skb(len);
+	if (!skb) {
+		dev->net->stats.rx_dropped++;
+		return -ENOMEM;
+	}
+
+	skb_put_data(skb, buf, len);
+	skb->dev = dev->net;
+	skb->protocol = eth_type_trans(skb, dev->net);
+
+	dev->net->stats.rx_packets++;
+	dev->net->stats.rx_bytes += len;
+	netif_rx(skb);
+
+	return 0;
+}
+
+static int ipheth_rcvbulk_callback_legacy(struct urb *urb)
+{
+	struct ipheth_device *dev;
+	char *buf;
+	int len;
+
+	dev = urb->context;
+
+	if (urb->actual_length <= IPHETH_IP_ALIGN) {
+		dev->net->stats.rx_length_errors++;
+		return -EINVAL;
+	}
+	len = urb->actual_length - IPHETH_IP_ALIGN;
+	buf = urb->transfer_buffer + IPHETH_IP_ALIGN;
+
+	return ipheth_consume_skb(buf, len, dev);
+}
+
+static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
+{
+	struct usb_cdc_ncm_nth16 *ncmh;
+	struct usb_cdc_ncm_ndp16 *ncm0;
+	struct usb_cdc_ncm_dpe16 *dpe;
+	struct ipheth_device *dev;
+	int retval = -EINVAL;
+	char *buf;
+	int len;
+
+	dev = urb->context;
+
+	if (urb->actual_length < IPHETH_NCM_HEADER_SIZE) {
+		dev->net->stats.rx_length_errors++;
+		return retval;
+	}
+
+	ncmh = urb->transfer_buffer;
+	if (ncmh->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN) ||
+	    le16_to_cpu(ncmh->wNdpIndex) >= urb->actual_length) {
+		dev->net->stats.rx_errors++;
+		return retval;
+	}
+
+	ncm0 = urb->transfer_buffer + le16_to_cpu(ncmh->wNdpIndex);
+	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN) ||
+	    le16_to_cpu(ncmh->wHeaderLength) + le16_to_cpu(ncm0->wLength) >=
+	    urb->actual_length) {
+		dev->net->stats.rx_errors++;
+		return retval;
+	}
+
+	dpe = ncm0->dpe16;
+	while (le16_to_cpu(dpe->wDatagramIndex) != 0 &&
+	       le16_to_cpu(dpe->wDatagramLength) != 0) {
+		if (le16_to_cpu(dpe->wDatagramIndex) >= urb->actual_length ||
+		    le16_to_cpu(dpe->wDatagramIndex) +
+		    le16_to_cpu(dpe->wDatagramLength) > urb->actual_length) {
+			dev->net->stats.rx_length_errors++;
+			return retval;
+		}
+
+		buf = urb->transfer_buffer + le16_to_cpu(dpe->wDatagramIndex);
+		len = le16_to_cpu(dpe->wDatagramLength);
+
+		retval = ipheth_consume_skb(buf, len, dev);
+		if (retval != 0)
+			return retval;
+
+		dpe++;
+	}
+
+	return 0;
+}
+
 static void ipheth_rcvbulk_callback(struct urb *urb)
 {
 	struct ipheth_device *dev;
-	struct sk_buff *skb;
-	int status;
-	char *buf;
-	int len;
+	int retval, status;
 
 	dev = urb->context;
 	if (dev == NULL)
···
 		dev->net->stats.rx_length_errors++;
 		return;
 	}
-	len = urb->actual_length - IPHETH_IP_ALIGN;
-	buf = urb->transfer_buffer + IPHETH_IP_ALIGN;
 
-	skb = dev_alloc_skb(len);
-	if (!skb) {
-		dev_err(&dev->intf->dev, "%s: dev_alloc_skb: -ENOMEM\n",
-			__func__);
-		dev->net->stats.rx_dropped++;
+	/* RX URBs starting with 0x00 0x01 do not encapsulate Ethernet frames,
+	 * but rather are control frames. Their purpose is not documented, and
+	 * they don't affect driver functionality, okay to drop them.
+	 * There is usually just one 4-byte control frame as the very first
+	 * URB received from the bulk IN endpoint.
+	 */
+	if (unlikely
+		(((char *)urb->transfer_buffer)[0] == 0 &&
+		 ((char *)urb->transfer_buffer)[1] == 1))
+		goto rx_submit;
+
+	retval = dev->rcvbulk_callback(urb);
+	if (retval != 0) {
+		dev_err(&dev->intf->dev, "%s: callback retval: %d\n",
+			__func__, retval);
 		return;
 	}
 
-	skb_put_data(skb, buf, len);
-	skb->dev = dev->net;
-	skb->protocol = eth_type_trans(skb, dev->net);
-
-	dev->net->stats.rx_packets++;
-	dev->net->stats.rx_bytes += len;
+rx_submit:
 	dev->confirmed_pairing = true;
-	netif_rx(skb);
 	ipheth_rx_submit(dev, GFP_ATOMIC);
 }
 
···
 	return retval;
 }
 
+static int ipheth_enable_ncm(struct ipheth_device *dev)
+{
+	struct usb_device *udev = dev->udev;
+	int retval;
+
+	retval = usb_control_msg(udev,
+				 usb_sndctrlpipe(udev, IPHETH_CTRL_ENDP),
+				 IPHETH_CMD_ENABLE_NCM, /* request */
+				 0x41, /* request type */
+				 0x00, /* value */
+				 0x02, /* index */
+				 NULL,
+				 0,
+				 IPHETH_CTRL_TIMEOUT);
+
+	dev_info(&dev->intf->dev, "%s: usb_control_msg: %d\n",
+		 __func__, retval);
+
+	return retval;
+}
+
 static int ipheth_rx_submit(struct ipheth_device *dev, gfp_t mem_flags)
 {
 	struct usb_device *udev = dev->udev;
···
 
 	usb_fill_bulk_urb(dev->rx_urb, udev,
 			  usb_rcvbulkpipe(udev, dev->bulk_in),
-			  dev->rx_buf, IPHETH_BUF_SIZE + IPHETH_IP_ALIGN,
+			  dev->rx_buf, dev->rx_buf_len,
 			  ipheth_rcvbulk_callback,
 			  dev);
 	dev->rx_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
···
 	int retval;
 
 	/* Paranoid */
-	if (skb->len > IPHETH_BUF_SIZE) {
+	if (skb->len > IPHETH_TX_BUF_SIZE) {
 		WARN(1, "%s: skb too large: %d bytes\n", __func__, skb->len);
 		dev->net->stats.tx_dropped++;
 		dev_kfree_skb_any(skb);
···
 	dev->net = netdev;
 	dev->intf = intf;
 	dev->confirmed_pairing = false;
+	dev->rx_buf_len = IPHETH_RX_BUF_SIZE_LEGACY;
+	dev->rcvbulk_callback = ipheth_rcvbulk_callback_legacy;
 	/* Set up endpoints */
 	hintf = usb_altnum_to_altsetting(intf, IPHETH_ALT_INTFNUM);
 	if (hintf == NULL) {
···
 	retval = ipheth_get_macaddr(dev);
 	if (retval)
 		goto err_get_macaddr;
+
+	retval = ipheth_enable_ncm(dev);
+	if (!retval) {
+		dev->rx_buf_len = IPHETH_RX_BUF_SIZE_NCM;
+		dev->rcvbulk_callback = ipheth_rcvbulk_callback_ncm;
+	}
 
 	INIT_DELAYED_WORK(&dev->carrier_work, ipheth_carrier_check_work);