From: Mateusz Guzik <mguzik@redhat.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Al Viro <viro@zeniv.linux.org.uk>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>,
Rainer Weikusat <rweikusat@mobileactivedefense.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
netdev <netdev@vger.kernel.org>,
Eric Dumazet <edumazet@google.com>,
syzkaller <syzkaller@googlegroups.com>
Subject: Re: fs, net: deadlock between bind/splice on af_unix
Date: Tue, 7 Feb 2017 15:20:35 +0100 [thread overview]
Message-ID: <20170207142035.vfnyrbggb6kbfzgd@dhcp-1-212.brq.redhat.com> (raw)
In-Reply-To: <CAM_iQpVG+ybcv1DAc01y3c=CRmUgMqocEnp-efhVM0c-t4hZ0w@mail.gmail.com>
On Sun, Feb 05, 2017 at 11:22:12PM -0800, Cong Wang wrote:
> On Tue, Jan 31, 2017 at 10:14 AM, Mateusz Guzik <mguzik@redhat.com> wrote:
> > On Mon, Jan 30, 2017 at 10:44:03PM -0800, Cong Wang wrote:
> >> Mind being more specific?
> >
> > Consider 2 threads which bind the same socket, but with different paths.
> >
> > Currently exactly one file will get created, the one used to bind.
> >
> > With your patch both threads can succeed creating their respective
> > files, but only one will manage to bind. The other one must error out,
> > but it already created a file it is unclear what to do with.
>
> In this case, it simply puts the path back:
>
> err = -EINVAL;
> if (u->addr)
> goto out_up;
> [...]
>
> out_up:
> mutex_unlock(&u->bindlock);
> out_put:
> if (err)
> path_put(&path);
> out:
> return err;
>
>
> Which is what unix_release_sock() does too:
>
> if (path.dentry)
> path_put(&path);
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.
What to do with the file now?
Untested, but likely a working solution would rework the code so that
e.g. a flag is set and the lock can be dropped.
next prev parent reply other threads:[~2017-02-07 14:20 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 14:47 fs, net: deadlock between bind/splice on af_unix Dmitry Vyukov
2016-12-08 16:30 ` Dmitry Vyukov
2016-12-09 0:08 ` Cong Wang
2016-12-09 1:32 ` Al Viro
2016-12-09 6:32 ` Cong Wang
2016-12-09 6:41 ` Al Viro
2017-01-16 9:32 ` Dmitry Vyukov
2017-01-17 21:21 ` Cong Wang
2017-01-18 9:17 ` Dmitry Vyukov
2017-01-20 4:57 ` Cong Wang
2017-01-20 22:52 ` Dmitry Vyukov
2017-01-23 19:00 ` Cong Wang
2017-01-26 23:29 ` Mateusz Guzik
2017-01-27 5:11 ` Cong Wang
2017-01-27 6:41 ` Mateusz Guzik
2017-01-31 6:44 ` Cong Wang
2017-01-31 18:14 ` Mateusz Guzik
2017-02-06 7:22 ` Cong Wang
2017-02-07 14:20 ` Mateusz Guzik [this message]
2017-02-10 1:37 ` Cong Wang
2017-01-17 8:07 ` Eric W. Biederman
[not found] ` <065031f0-27c5-443d-82f9-2f475fcef8c3@googlegroups.com>
2017-06-23 16:30 ` Cong Wang
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