[PATCH 3.16 125/133] net: cdc_ether: fix divide by 0 on bad descriptors

[Ben Hutchings]

3.16.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: BjÃrn Mork <bjorn@xxxxxxx>

commit 2cb80187ba065d7decad7c6614e35e07aec8a974 upstream.

Setting dev->hard_mtu to 0 will cause a divide error in
usbnet_probe. Protect against devices with bogus CDC Ethernet
functional descriptors by ignoring a zero wMaxSegmentSize.

Signed-off-by: BjÃrn Mork <bjorn@xxxxxxx>
Acked-by: Oliver Neukum <oneukum@xxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: parsing code is organised differently]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/net/usb/cdc_ether.c
+++ b/drivers/net/usb/cdc_ether.c
@@ -235,8 +235,9 @@ int usbnet_generic_cdc_bind(struct usbne
 					info->ether->bLength);
 				goto bad_desc;
 			}
-			dev->hard_mtu = le16_to_cpu(
-						info->ether->wMaxSegmentSize);
+			if (info->ether->wMaxSegmentSize)
+				dev->hard_mtu = le16_to_cpu(
+					info->ether->wMaxSegmentSize);
 			/* because of Zaurus, we may be ignoring the host
 			 * side link address we were given.
 			 */