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Date: Wed, 4 Mar 2026 14:28:24 +0100
From: Florian Westphal <fw@strlen.de>
To: Phil Sutter <phil@nwl.cc>, Pablo Neira Ayuso <pablo@netfilter.org>,
	Helen Koike <koike@igalia.com>, netfilter-devel@vger.kernel.org,
	coreteam@netfilter.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel-dev@igalia.com
Subject: Re: [PATCH] netfilter: nf_tables: fix use-after-free on ops->dev
Message-ID: <aagzeEIkk1v4OmJk@strlen.de>
References: <20260302212605.689909-1-koike@igalia.com>
 <aaYYiPTO5JYOlhhY@chamomile>
 <aagqaq6LNJnrg8eC@orbyte.nwl.cc>
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Phil Sutter <phil@nwl.cc> wrote:
> But isn't __nf_unregister_net_hook() still called immediately when
> handling NETDEV_UNREGISTER event? I guess struct nf_hook_ops::dev may
> still be accessed afterwards since ops is RCU-freed. Is Helen's report
> inaccurate in that regard?

Its a red herring.

The device is registered twice.  But UNREGISTER only removes ONE
instance.

Then, later, when a different device (same name!) invokes netlink handler,
the walk finds the old, free'd net_device.

I hacked UNREGISTER to handle this: no more splat.
I reverted this change and altered REGISTER to never allow
double-register: no splats.