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Date:   Wed, 22 Nov 2017 01:58:13 +0000
From:   Ben Hutchings <>
CC:, "David S. Miller" <>,
        "Bjørn Mork" <>,
        "Oliver Neukum" <>
Subject: [PATCH 3.16 125/133] net: cdc_ether: fix divide by 0 on bad

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


From: Bjørn Mork <>

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 <>
Acked-by: Oliver Neukum <>
Signed-off-by: David S. Miller <>
[bwh: Backported to 3.16: parsing code is organised differently]
Signed-off-by: Ben Hutchings <>
--- 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
 				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.

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