Re: [syzbot] divide error in usbnet_start_xmit

On 19.10.21 05:17, syzbot wrote:

quoted

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@syzkaller.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@suse.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@suse.com>
Reported-by: syzbot+76bb1d34ffa0adc03baa@syzkaller.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;