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From: Hannes Frederic Sowa <hannes@stressinduktion.org>
To: Eric Dumazet <eric.dumazet@gmail.com>,
        Rainer Weikusat <rweikusat@mobileactivedefense.com>
Cc: Eric Dumazet <edumazet@google.com>, Dmitry Vyukov <dvyukov@google.com>,
        Benjamin LaHaise <bcrl@kvack.org>,
        "David S. Miller" <davem@davemloft.net>,
        Al Viro <viro@zeniv.linux.org.uk>, David Howells <dhowells@redhat.com>,
        Ying Xue <ying.xue@windriver.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        netdev <netdev@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>
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Subject: Re: use-after-free in sock_wake_async
Date: Wed, 25 Nov 2015 23:32:12 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1609
Lines: 43

On Wed, Nov 25, 2015, at 23:09, Eric Dumazet wrote:
> On Wed, 2015-11-25 at 20:57 +0000, Rainer Weikusat wrote:
> 
> > I do agree that keeping the ->sk_data_ready outside of the lock will
> > very likely have performance advantages. That's just something I
> > wouldn't have undertaken because I'd be reluctant to make a fairly
> > complicated change to a lot of code.
> 
> All I am saying is that we can keep current performance.
> 
> We already have the core infrastructure, we only need to properly use
> it.
> 
> I will split my changes in two parts.
> 
> One part doing a very boring change of
> 
> rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA
> for X in SOCK_ASYNC_NOSPACE SOCK_ASYNC_WAITDATA 
> 
>  set_bit(X, &sk->sk_socket->flags) -> sk_set_bit(X, sk)
>  clear_bit(X, &sk->sk_socket->flags) -> sk_clear_bit(X, sk)

sk_set_bit and sk_clear_bit will forward the set_bit and clear_bit into
the socket_wq like you explained above?

> The rename will help backports to catch code that might have been
> removed in recent kernels.
> 
> Then the second patch will do the actual changes, and they will look
> very sensible for people wanting to review them, and or familiar with
> the stack, do not worry ;)

Do you see a chance to inline socket_wq into struct socket and discard
struct socket_alloc in one go by rcu in socket_destroy_inode?

Thanks,
Hannes
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