From foo@baz Tue 01 Oct 2019 03:27:55 PM CEST
From: Oliver Neukum <oneukum@suse.com>
Date: Thu, 19 Sep 2019 10:23:08 +0200
Subject: usbnet: sanity checking of packet sizes and device mtu

From: Oliver Neukum <oneukum@suse.com>

[ Upstream commit 280ceaed79f18db930c0cc8bb21f6493490bf29c ]

After a reset packet sizes and device mtu can change and need
to be reevaluated to calculate queue sizes.
Malicious devices can set this to zero and we divide by it.
Introduce sanity checking.

Reported-and-tested-by:  syzbot+6102c120be558c885f04@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/usb/usbnet.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -344,6 +344,8 @@ void usbnet_update_max_qlen(struct usbne
 {
 	enum usb_device_speed speed = dev->udev->speed;
 
+	if (!dev->rx_urb_size || !dev->hard_mtu)
+		goto insanity;
 	switch (speed) {
 	case USB_SPEED_HIGH:
 		dev->rx_qlen = MAX_QUEUE_MEMORY / dev->rx_urb_size;
@@ -360,6 +362,7 @@ void usbnet_update_max_qlen(struct usbne
 		dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;
 		break;
 	default:
+insanity:
 		dev->rx_qlen = dev->tx_qlen = 4;
 	}
 }