From: Hannes Frederic Sowa <hannes@stressinduktion•org>
To: David Miller <davem@davemloft•net>
Cc: daniel@iogearbox•net, eric.dumazet@gmail•com,
alexei.starovoitov@gmail•com, mkubecek@suse•cz,
sasha.levin@oracle•com, jslaby@suse•cz, mst@redhat•com,
netdev@vger•kernel.org
Subject: Re: [PATCH net] tun, bpf: fix suspicious RCU usage in tun_{attach,detach}_filter
Date: Thu, 31 Mar 2016 21:48:27 +0200 [thread overview]
Message-ID: <56FD7F0B.5090602@stressinduktion.org> (raw)
In-Reply-To: <20160331.153630.1640223846173244431.davem@davemloft.net>
On 31.03.2016 21:36, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@stressinduktion•org>
> Date: Thu, 31 Mar 2016 21:24:12 +0200
>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 4b81b71171b4ce..8ab270d5ce5507 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -1166,7 +1166,8 @@ static int __sk_attach_prog(struct bpf_prog
>> *prog, struct sock *sk)
>> }
>>
>> old_fp = rcu_dereference_protected(sk->sk_filter,
>> - sock_owned_by_user(sk));
>> + lockdep_rtnl_is_held() ||
>> + lockdep_sock_is_held(sk));
>> rcu_assign_pointer(sk->sk_filter, fp);
>>
>> if (old_fp)
>
> I have the same objections Daniel did.
>
> Not all socket filter clients use RTNL as the synchornization
> mechanism. The caller, or some descriptive element, should tell us
> what that synchronizing element is.
>
> Yes, I understand how these RTNL checks can pass "accidently" but
> the opposite is true too. A socket locking synchornizing user,
> who didn't lock the socket, might now pass because RTNL happens
> to be held elsewhere.
Actually lockdep_rtnl_is_held checks if this specific code/thread holds
the lock and no other cpu/thread. So it will not pass here in case
another cpu has the lock.
lockdep stores the current held locks in current->held_locks, if we
preempt we switch current pointer, if we take a spin_lock we can't sleep
thus not preempt. Thus we always know that this specific code has the lock.
Using sock_owned_by_user actually has this problem, and thus I am
replacing it. We don't know who has the socket locked.
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());
Bye,
Hannes
next prev parent reply other threads:[~2016-03-31 19:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-31 0:13 [PATCH net] tun, bpf: fix suspicious RCU usage in tun_{attach,detach}_filter Daniel Borkmann
2016-03-31 1:18 ` Alexei Starovoitov
2016-03-31 5:01 ` Michal Kubecek
2016-03-31 5:08 ` Alexei Starovoitov
2016-03-31 5:22 ` Michal Kubecek
2016-03-31 5:43 ` Alexei Starovoitov
2016-03-31 11:35 ` Daniel Borkmann
2016-03-31 11:59 ` Eric Dumazet
2016-03-31 12:16 ` Daniel Borkmann
2016-03-31 19:21 ` David Miller
2016-03-31 19:24 ` Hannes Frederic Sowa
2016-03-31 19:31 ` Alexei Starovoitov
2016-03-31 19:48 ` David Miller
2016-03-31 19:36 ` David Miller
2016-03-31 19:48 ` Hannes Frederic Sowa [this message]
2016-03-31 19:50 ` David Miller
2016-03-31 21:52 ` Daniel Borkmann
2016-03-31 23:31 ` Hannes Frederic Sowa
2016-03-31 12:12 ` Hannes Frederic Sowa
2016-03-31 9:15 ` Jiri Slaby
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