net: cdc_ether: fix divide by 0 on bad descriptors

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: Bjørn Mork <bjorn@mork.no>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: parsing code is organised differently]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/usb/cdc_ether.c b/drivers/net/usb/cdc_ether.c
index 43aa06b3f7c6949b353b8e466fde81c53bbbecca..a1ca4745d706646bf2fa1eb17ffcba89dacb6247 100644 (file)
--- a/drivers/net/usb/cdc_ether.c
+++ b/drivers/net/usb/cdc_ether.c
@@ -234,8 +234,9 @@ int usbnet_generic_cdc_bind(struct usbnet *dev, struct usb_interface *intf)
                                        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.
                         */