1 files changed, 52 insertions, 35 deletions

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 46afb95ffabe..bb1364f85bd1 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -61,7 +61,18 @@
 #define IPHETH_USBINTF_PROTO    1
 
 #define IPHETH_IP_ALIGN		2	/* padding at front of URB */
-#define IPHETH_NCM_HEADER_SIZE  (12 + 96) /* NCMH + NCM0 */
+/* On iOS devices, NCM headers in RX have a fixed size regardless of DPE count:
+ * - NTH16 (NCMH): 12 bytes, as per CDC NCM 1.0 spec
+ * - NDP16 (NCM0): 96 bytes, of which
+ *    - NDP16 fixed header: 8 bytes
+ *    - maximum of 22 DPEs (21 datagrams + trailer), 4 bytes each
+ */
+#define IPHETH_NDP16_MAX_DPE	22
+#define IPHETH_NDP16_HEADER_SIZE (sizeof(struct usb_cdc_ncm_ndp16) + \
+				  IPHETH_NDP16_MAX_DPE * \
+				  sizeof(struct usb_cdc_ncm_dpe16))
+#define IPHETH_NCM_HEADER_SIZE	(sizeof(struct usb_cdc_ncm_nth16) + \
+				 IPHETH_NDP16_HEADER_SIZE)
 #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
@@ -207,15 +218,23 @@ static int ipheth_rcvbulk_callback_legacy(struct urb *urb)
 	return ipheth_consume_skb(buf, len, dev);
 }
 
+/* In "NCM mode", the iOS device encapsulates RX (phone->computer) traffic
+ * in NCM Transfer Blocks (similarly to CDC NCM). However, unlike reverse
+ * tethering (handled by the `cdc_ncm` driver), regular tethering is not
+ * compliant with the CDC NCM spec, as the device is missing the necessary
+ * descriptors, and TX (computer->phone) traffic is not encapsulated
+ * at all. Thus `ipheth` implements a very limited subset of the spec with
+ * the sole purpose of parsing RX URBs.
+ */
 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;
+	u16 dg_idx, dg_len;
 	int retval = -EINVAL;
 	char *buf;
-	int len;
 
 	dev = urb->context;
 
@@ -226,40 +245,42 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 
 	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;
-	}
+	    /* On iOS, NDP16 directly follows NTH16 */
+	    ncmh->wNdpIndex != cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16)))
+		goto rx_error;
 
-	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;
-	}
+	ncm0 = urb->transfer_buffer + sizeof(struct usb_cdc_ncm_nth16);
+	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN))
+		goto rx_error;
 
 	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) {
+	for (int dpe_i = 0; dpe_i < IPHETH_NDP16_MAX_DPE; ++dpe_i, ++dpe) {
+		dg_idx = le16_to_cpu(dpe->wDatagramIndex);
+		dg_len = le16_to_cpu(dpe->wDatagramLength);
+
+		/* Null DPE must be present after last datagram pointer entry
+		 * (3.3.1 USB CDC NCM spec v1.0)
+		 */
+		if (dg_idx == 0 && dg_len == 0)
+			return 0;
+
+		if (dg_idx < IPHETH_NCM_HEADER_SIZE ||
+		    dg_idx >= urb->actual_length ||
+		    dg_len > urb->actual_length - dg_idx) {
 			dev->net->stats.rx_length_errors++;
 			return retval;
 		}
 
-		buf = urb->transfer_buffer + le16_to_cpu(dpe->wDatagramIndex);
-		len = le16_to_cpu(dpe->wDatagramLength);
+		buf = urb->transfer_buffer + dg_idx;
 
-		retval = ipheth_consume_skb(buf, len, dev);
+		retval = ipheth_consume_skb(buf, dg_len, dev);
 		if (retval != 0)
 			return retval;
-
-		dpe++;
 	}
 
-	return 0;
+rx_error:
+	dev->net->stats.rx_errors++;
+	return retval;
 }
 
 static void ipheth_rcvbulk_callback(struct urb *urb)
@@ -552,11 +573,10 @@ static int ipheth_probe(struct usb_interface *intf,
 			const struct usb_device_id *id)
 {
 	struct usb_device *udev = interface_to_usbdev(intf);
+	struct usb_endpoint_descriptor *ep_in, *ep_out;
 	struct usb_host_interface *hintf;
-	struct usb_endpoint_descriptor *endp;
 	struct ipheth_device *dev;
 	struct net_device *netdev;
-	int i;
 	int retval;
 
 	netdev = alloc_etherdev(sizeof(struct ipheth_device));
@@ -582,19 +602,16 @@ static int ipheth_probe(struct usb_interface *intf,
 		goto err_endpoints;
 	}
 
-	for (i = 0; i < hintf->desc.bNumEndpoints; i++) {
-		endp = &hintf->endpoint[i].desc;
-		if (usb_endpoint_is_bulk_in(endp))
-			dev->bulk_in = endp->bEndpointAddress;
-		else if (usb_endpoint_is_bulk_out(endp))
-			dev->bulk_out = endp->bEndpointAddress;
-	}
-	if (!(dev->bulk_in && dev->bulk_out)) {
-		retval = -ENODEV;
+	retval = usb_find_common_endpoints_reverse(hintf, &ep_in, &ep_out,
+						   NULL, NULL);
+	if (retval) {
 		dev_err(&intf->dev, "Unable to find endpoints\n");
 		goto err_endpoints;
 	}
 
+	dev->bulk_in = ep_in->bEndpointAddress;
+	dev->bulk_out = ep_out->bEndpointAddress;
+
 	dev->ctrl_buf = kmalloc(IPHETH_CTRL_BUF_SIZE, GFP_KERNEL);
 	if (dev->ctrl_buf == NULL) {
 		retval = -ENOMEM;