netdev - Re: [PATCH net] tun, bpf: fix suspicious RCU usage in tun_{attach,detach}

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Date:	Thu, 31 Mar 2016 23:52:57 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>
CC:	eric.dumazet@...il.com, alexei.starovoitov@...il.com,
	mkubecek@...e.cz, sasha.levin@...cle.com, jslaby@...e.cz,
	mst@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] tun, bpf: fix suspicious RCU usage in tun_{attach,detach}_filter

On 03/31/2016 09:48 PM, Hannes Frederic Sowa wrote:
[...]
> Tightest solution would probably be to combine both patches.
>
> bool called_by_tuntap;
>
> old_fp = rcu_dereference_protected(sk->sk_filter, called_by_tuntap ? lockdep_rtnl_is_held() : lockdep_sock_is_held());

If I understand you correctly with combining them, you mean you'd still
need the API change to pass the bool 'called_by_tuntap' down, right?

If so, your main difference is, after all, to replace the sock_owned_by_user()
with the lockdep_sock_is_held() construction instead, correct?

But then, isn't it already sufficient when you pass the bool itself down
that 'demuxes' in this case between the sock_owned_by_user() vs
lockdep_rtnl_is_held() check?

Thanks,
Daniel