[PATCH] usbnet: sanity checking of packet sizes and device mtu

[Oliver Neukum]

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+6102c120be558c885...@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneu...@suse.com>
---
 drivers/net/usb/usbnet.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 58952a79b05f..e44849499b89 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -339,6 +339,8 @@ void usbnet_update_max_qlen(struct usbnet *dev)
 {
        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;
@@ -355,6 +357,7 @@ void usbnet_update_max_qlen(struct usbnet *dev)
                dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;
                break;
        default:
+insanity:
                dev->rx_qlen = dev->tx_qlen = 4;
        }
 }
-- 
2.16.4