linux-kernel - Re: [PATCH] net: arp, ipv6: handle special case of tap device

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Date:   Wed, 3 Oct 2018 09:25:12 -0400 (EDT)
From:   Vladis Dronov <vdronov@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, syzkaller@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: arp, ipv6: handle special case of tap device

> From: "David Miller" <davem@...emloft.net>
> Sent: Wednesday, October 3, 2018 7:25:40 AM
>
> > Probably, this functionality is already used by some userspace, so I
> > believe, I cannot just remove TUNSETLINK ioctl.
> 
> Who uses it, how do they use it, and what do they sanely expect about
> the link layer header properties of a tap device which has had ->type
> changed?

Honestly, I have no idea. I was working on a syzkaller bug report and
found that the reason for that bug was TUNSETLINK ioctl.

This ioctl was introduced 13 years ago with ff4cc3ac93e1d and it says:

> For use with
> wireless and other networking types it should be possible to set the
> ARP type via an ioctl.

, that's all. Let me try to prepare a patch that sets dev->addr_len and
dev->broadcast according to dev->type. I would probably need an advise
what other fields must be adjusted too.

Otherwise, we can just to remove the TUNSETLINK ioctl.

Best regards,
Vladis Dronov | Red Hat, Inc. | Product Security Engineer