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

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Date:	Fri, 1 Apr 2016 01:31:52 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Daniel Borkmann <daniel@...earbox.net>,
	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

Hi Daniel,

On 31.03.2016 23:52, Daniel Borkmann wrote:
> 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?

I actually decided to simply lock the sockets. So that there will always 
be a clear lock owner during the updates. I think this is cleaner. What 
do you think?

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

I just didn't do that part because we hold socket lock now.

> 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?

I just send out the patches, please have a look.

Thanks,
Hannes