usbnet: remove generic hard_header_len check

This patch removes a generic hard_header_len check from the usbnet
module that is causing dropped packages under certain circumstances
for devices that send rx packets that cross urb boundaries.

One example is the AX88772B which occasionally send rx packets that
cross urb boundaries where the remaining partial packet is sent with
no hardware header. When the buffer with a partial packet is of less
number of octets than the value of hard_header_len the buffer is
discarded by the usbnet module.

With AX88772B this can be reproduced by using ping with a packet
size between 1965-1976.

The bug has been reported here:

https://bugzilla.kernel.org/show_bug.cgi?id=29082

This patch introduces the following changes:
- Removes the generic hard_header_len check in the rx_complete
function in the usbnet module.
- Introduces a ETH_HLEN check for skbs that are not cloned from
within a rx_fixup callback.
- For safety a hard_header_len check is added to each rx_fixup
callback function that could be affected by this change.
These extra checks could possibly be removed by someone
who has the hardware to test.
- Removes a call to dev_kfree_skb_any() and instead utilizes the
dev->done list to queue skbs for cleanup.

The changes place full responsibility on the rx_fixup callback
functions that clone skbs to only pass valid skbs to the
usbnet_skb_return function.

Signed-off-by: Emil Goode <[e-mail]>
Reported-by: Igor Gnatenko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/usb/ax88179_178a.c

···
 	u16 hdr_off;
 	u32 *pkt_hdr;
 
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	skb_trim(skb, skb->len - 4);
 	memcpy(&rx_hdr, skb_tail_pointer(skb), 4);
 	le32_to_cpus(&rx_hdr);

drivers/net/usb/gl620a.c

···
 	u32			size;
 	u32			count;
 
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	header = (struct gl_header *) skb->data;
 
 	// get the packet count of the received skb

drivers/net/usb/mcs7830.c

···
 {
 	u8 status;
 
-	if (skb->len == 0) {
-		dev_err(&dev->udev->dev, "unexpected empty rx frame\n");
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len) {
+		dev_err(&dev->udev->dev, "unexpected tiny rx frame\n");
 		return 0;
 	}
 

drivers/net/usb/net1080.c

···
 	struct nc_trailer	*trailer;
 	u16			hdr_len, packet_len;
 
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	if (!(skb->len & 0x01)) {
 		netdev_dbg(dev->net, "rx framesize %d range %d..%d mtu %d\n",
 			   skb->len, dev->net->hard_header_len, dev->hard_mtu,

drivers/net/usb/qmi_wwan.c

···
 {
 	__be16 proto;
 
-	/* usbnet rx_complete guarantees that skb->len is at least
-	 * hard_header_len, so we can inspect the dest address without
-	 * checking skb->len
-	 */
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	switch (skb->data[0] & 0xf0) {
 	case 0x40:
 		proto = htons(ETH_P_IP);

drivers/net/usb/rndis_host.c

···
  */
 int rndis_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	/* peripheral may have batched packets to us... */
 	while (likely(skb->len)) {
 		struct rndis_data_hdr	*hdr = (void *)skb->data;

drivers/net/usb/smsc75xx.c

···
 
 static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	while (skb->len > 0) {
 		u32 rx_cmd_a, rx_cmd_b, align_count, size;
 		struct sk_buff *ax_skb;

drivers/net/usb/smsc95xx.c

···
 
 static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	while (skb->len > 0) {
 		u32 header, align_count;
 		struct sk_buff *ax_skb;

drivers/net/usb/sr9800.c

···
 {
 	int offset = 0;
 
+	/* This check is no longer done by usbnet */
+	if (skb->len < dev->net->hard_header_len)
+		return 0;
+
 	while (offset + sizeof(u32) < skb->len) {
 		struct sk_buff *sr_skb;
 		u16 size;

drivers/net/usb/usbnet.c

···
 	}
 	// else network stack removes extra byte if we forced a short packet
 
-	if (skb->len) {
-		/* all data was already cloned from skb inside the driver */
-		if (dev->driver_info->flags & FLAG_MULTI_PACKET)
-			dev_kfree_skb_any(skb);
-		else
-			usbnet_skb_return(dev, skb);
+	/* all data was already cloned from skb inside the driver */
+	if (dev->driver_info->flags & FLAG_MULTI_PACKET)
+		goto done;
+
+	if (skb->len < ETH_HLEN) {
+		dev->net->stats.rx_errors++;
+		dev->net->stats.rx_length_errors++;
+		netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);
+	} else {
+		usbnet_skb_return(dev, skb);
 		return;
 	}
 
-	netif_dbg(dev, rx_err, dev->net, "drop\n");
-	dev->net->stats.rx_errors++;
 done:
 	skb_queue_tail(&dev->done, skb);
 }
···
 	switch (urb_status) {
 	/* success */
 	case 0:
-		if (skb->len < dev->net->hard_header_len) {
-			state = rx_cleanup;
-			dev->net->stats.rx_errors++;
-			dev->net->stats.rx_length_errors++;
-			netif_dbg(dev, rx_err, dev->net,
-				  "rx length %d\n", skb->len);
-		}
 		break;
 
 	/* stalls need manual reset. this is rare ... except that