netdev - Re: [PATCH] bonding: do not enslave CAN devices

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Date:   Wed, 26 Feb 2020 20:23:26 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     mkl@...gutronix.de
Cc:     socketcan@...tkopp.net, linux-can@...r.kernel.org,
        netdev@...r.kernel.org,
        syzbot+c3ea30e1e2485573f953@...kaller.appspotmail.com,
        dvyukov@...gle.com, j.vosburgh@...il.com, vfalico@...il.com,
        andy@...yhouse.net, stable@...r.kernel.org
Subject: Re: [PATCH] bonding: do not enslave CAN devices

From: Marc Kleine-Budde <mkl@...gutronix.de>
Date: Tue, 25 Feb 2020 21:32:41 +0100

> On 1/30/20 2:30 PM, Oliver Hartkopp wrote:
>> Since commit 8df9ffb888c ("can: make use of preallocated can_ml_priv for per
>> device struct can_dev_rcv_lists") the device specific CAN receive filter lists
>> are stored in netdev_priv() and dev->ml_priv points to these filters.
>> 
>> In the bug report Syzkaller enslaved a vxcan1 CAN device and accessed the
>> bonding device with a PF_CAN socket which lead to a crash due to an access of
>> an unhandled bond_dev->ml_priv pointer.
>> 
>> Deny to enslave CAN devices by the bonding driver as the resulting bond_dev
>> pretends to be a CAN device by copying dev->type without really being one.
>> 
>> Reported-by: syzbot+c3ea30e1e2485573f953@...kaller.appspotmail.com
>> Fixes: 8df9ffb888c ("can: make use of preallocated can_ml_priv for per
>> device struct can_dev_rcv_lists")
>> Cc: linux-stable <stable@...r.kernel.org> # >= v5.4
>> Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>
> Acked-by: Marc Kleine-Budde <mkl@...gutronix.de>
> 
> What's the preferred to upstream this? I could take this via the
> linux-can tree.

What I don't get is why the PF_CAN is blindly dereferencing a device
assuming what is behind bond_dev->ml_priv.

If it assumes a device it access is CAN then it should check the
device by comparing the netdev_ops or via some other means.

This restriction seems arbitrary.