netdev - Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real

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Message-ID: <87czn0tc5s.fsf@nvidia.com>
Date:   Tue, 16 Nov 2021 15:20:31 +0100
From:   Petr Machata <petrm@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Petr Machata <petrm@...dia.com>,
        Ziyang Xuan <william.xuanziyang@...wei.com>,
        <davem@...emloft.net>, <jgg@...dia.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()


Jakub Kicinski <kuba@...nel.org> writes:

> On Mon, 15 Nov 2021 18:04:42 +0100 Petr Machata wrote:
>
>> I'm not sure why this wasn't happening before. After the veto,
>> register_vlan_dev() follows with a goto out_unregister_netdev, which
>> calls unregister_netdevice() calls unregister_netdevice_queue(), which
>> issues a notifier NETDEV_UNREGISTER, which invokes vlan_device_event(),
>> which calls unregister_vlan_dev(), which used to dev_put(real_dev),
>> which seems like it should have caused the same issue. Dunno.
>
> Does the notifier trigger unregister_vlan_dev()? I thought the notifier
> triggers when lower dev is unregistered.

Right, I misinterpreted this bit:

        vlan_info = rtnl_dereference(dev->vlan_info);
        if (!vlan_info)
                goto out;