Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()

From: Petr Machata <petrm@nvidia.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Petr Machata <petrm@nvidia.com>,
	Ziyang Xuan <william.xuanziyang@huawei.com>,
	<davem@davemloft.net>, <jgg@nvidia.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()
Date: Tue, 16 Nov 2021 15:20:31 +0100	[thread overview]
Message-ID: <87czn0tc5s.fsf@nvidia.com> (raw)
In-Reply-To: <20211115094940.138d86dc@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

Jakub Kicinski <kuba@kernel.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;