net: cdc_ether: fix divide by 0 on bad descriptors

bmork · gregkh · commit caeeef8438c3 · 2017-11-21T09:21:18.000+01:00
commit 2cb80187ba065d7decad7c6614e35e07aec8a974 upstream.

Setting dev-&gt;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 &lt;bjorn@mork.no&gt;
Acked-by: Oliver Neukum &lt;oneukum@suse.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
Signed-off-by: Ben Hutchings &lt;ben.hutchings@codethink.co.uk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
diff --git a/drivers/net/usb/cdc_ether.c b/drivers/net/usb/cdc_ether.c
@@ -221,7 +221,7 @@ int usbnet_generic_cdc_bind(struct usbnet *dev, struct usb_interface *intf)
 			goto bad_desc;
 	}
 
-	if (header.usb_cdc_ether_desc) {
+	if (header.usb_cdc_ether_desc && 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.

Original file line number	Diff line number	Diff line change
`@@ -221,7 +221,7 @@ int usbnet_generic_cdc_bind(struct usbnet dev, struct usb_interface intf)`
`221`	`221`	`goto bad_desc;`
`222`	`222`	`}`
`223`	`223`
`224`		`- if (header.usb_cdc_ether_desc) {`
	`224`	`+ if (header.usb_cdc_ether_desc && info->ether->wMaxSegmentSize) {`
`225`	`225`	`dev->hard_mtu = le16_to_cpu(info->ether->wMaxSegmentSize);`
`226`	`226`	`/* because of Zaurus, we may be ignoring the host`
`227`	`227`	`* side link address we were given.`