linux-kernel - Re: fs, net: deadlock between bind/splice on af

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Message-ID: <CAM_iQpUibPgC6kW2JmkhmPneZ6p7z6QjYdAQ8ng+pxtiWJ7xVA@mail.gmail.com>
Date:   Thu, 9 Feb 2017 17:37:56 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Mateusz Guzik <mguzik@...hat.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Rainer Weikusat <rweikusat@...ileactivedefense.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: fs, net: deadlock between bind/splice on af_unix

On Tue, Feb 7, 2017 at 6:20 AM, Mateusz Guzik <mguzik@...hat.com> wrote:
>
> Yes, but unix_release_sock is expected to leave the file behind.
> Note I'm not claiming there is a leak, but that racing threads will be
> able to trigger a condition where you create a file and fail to bind it.
>

Which is expected, right? No one guarantees the success of file
creation is the success of bind, the previous code does but it is not
part of API AFAIK. Should a sane user-space application check
the file creation for a successful bind() or just check its return value?

> What to do with the file now?
>

We just do what unix_release_sock() does, so why do you keep
asking the same question?

If you still complain about the race with user-space, think about the
same race in-between a successful bind() and close(), nothing is new.