linux-kernel - [PATCH 3.2 59/61] net: cdc_ether: fix divide by 0 on bad descriptors

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Date:   Wed, 22 Nov 2017 02:11:06 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Bjørn Mork" <bjorn@...k.no>,
        "Oliver Neukum" <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.2 59/61] net: cdc_ether: fix divide by 0 on bad descriptors

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

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

From: Bjørn Mork <bjorn@...k.no>

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@...k.no>
Acked-by: Oliver Neukum <oneukum@...e.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2: parsing code is organised differently]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/net/usb/cdc_ether.c
+++ b/drivers/net/usb/cdc_ether.c
@@ -234,8 +234,9 @@ 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.
 			 */