Re: divide error in usbnet_update_max_qlen

[Oliver Neukum <oneukum@suse.com>]

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Am Montag, den 16.09.2019, 06:29 -0700 schrieb syzbot:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    f0df5c1b usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=117659fa600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
> dashboard link: https://syzkaller.appspot.com/bug?extid=6102c120be558c885f04
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12107ba9600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=146014e6600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+6102c120be558c885f04@syzkaller.appspotmail.com

#syz test: https://github.com/google/kasan.git f0df5c1b

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From 57c2443b2a7678a6f7f6437f741f49f06a5104fb Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@suse.com>
Date: Tue, 17 Sep 2019 11:51:55 +0200
Subject: [PATCH] usbnet: sanity checking of packet sizes

Malicious devices can set this to zero and we divide by it.
Introduce sanity checking.

Signed-off-by: Oliver Neukum <oneukum@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