From: Rainer Weikusat <rweikusat@mobileactivedefense.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Rainer Weikusat <rweikusat@mobileactivedefense.com>,
        Eric Dumazet <edumazet@google.com>, Dmitry Vyukov <dvyukov@google.com>,
        Benjamin LaHaise <bcrl@kvack.org>,
        "David S. Miller" <davem@davemloft.net>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        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>
Subject: Re: use-after-free in sock_wake_async
In-Reply-To: <1448483017.24696.33.camel@edumazet-glaptop2.roam.corp.google.com>
	(Eric Dumazet's message of "Wed, 25 Nov 2015 12:23:37 -0800")
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Date: Wed, 25 Nov 2015 20:57:59 +0000
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Eric Dumazet <eric.dumazet@gmail.com> writes:
> On Wed, 2015-11-25 at 11:50 -0800, Eric Dumazet wrote:
>
>> >                 other->sk_data_ready(other);
>> > +               unix_state_unlock(other);
>
>
> Also, problem with such construct is that we wakeup a thread that will
> block on the lock we hold.
>
> Beauty of sk_data_ready() is to call it once we hold no lock any more,
> to enable another cpu to immediately proceed.
>
> In this case, 'other' can not disappear, so it should be safe.

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 in order to improve performance
unless performance was actually found to be lacking and because it would
step onto to many different people's turf.
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