netdev - Re: [syzbot] divide error in usbnet_start

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Message-ID: <c5a75b9b-bc2b-2bd8-f57c-833e6ca4c192@suse.com>
Date:   Tue, 19 Oct 2021 10:14:20 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     syzbot <syzbot+76bb1d34ffa0adc03baa@...kaller.appspotmail.com>,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] divide error in usbnet_start_xmit


On 19.10.21 05:17, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    c03fb16bafdf Merge 5.15-rc6 into usb-next
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=12d48f1f300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c27d285bdb7457e2
> dashboard link: https://syzkaller.appspot.com/bug?extid=76bb1d34ffa0adc03baa
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14fe6decb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c7bcaf300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+76bb1d34ffa0adc03baa@...kaller.appspotmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git c03fb16bafdf

>From a5270791d4480e9a6bc009c69a4454039aa160e7 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@...e.com>
Date: Tue, 19 Oct 2021 10:02:42 +0200
Subject: [PATCH] usbnet: sanity check for maxpacket

We cannot leave maxpacket at 0 because we divide by it.
Devices that give us a 0 there are unlikely to work, but let's
assume a 1, so we don't oops and a least try to operate.

Signed-off-by: Oliver Neukum <oneukum@...e.com>
Reported-by: syzbot+76bb1d34ffa0adc03baa@...kaller.appspotmail.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 840c1c2ab16a..2bdc3e0c1579 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1788,6 +1788,9 @@ usbnet_probe (struct usb_interface *udev, const
struct usb_device_id *prod)
     if (!dev->rx_urb_size)
         dev->rx_urb_size = dev->hard_mtu;
     dev->maxpacket = usb_maxpacket (dev->udev, dev->out, 1);
+    if (dev->maxpacket == 0)
+        /* that is a strange device */
+        dev->maxpacket = 1;
 
     /* let userspace know we have a random address */
     if (ether_addr_equal(net->dev_addr, node_id))
-- 
2.26.2