From: ebiederm@xmission.com (Eric W. Biederman)
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Dmitry Vyukov <dvyukov@google.com>,
"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, 17 Jan 2017 21:07:05 +1300 [thread overview]
Message-ID: <87wpduaz4m.fsf@xmission.com> (raw)
In-Reply-To: <20161209064144.GZ1555@ZenIV.linux.org.uk> (Al Viro's message of "Fri, 9 Dec 2016 06:41:44 +0000")
Al Viro <viro@ZenIV.linux.org.uk> writes:
> On Thu, Dec 08, 2016 at 10:32:00PM -0800, Cong Wang wrote:
>
>> > Why do we do autobind there, anyway, and why is it conditional on
>> > SOCK_PASSCRED? Note that e.g. for SOCK_STREAM we can bloody well get
>> > to sending stuff without autobind ever done - just use socketpair()
>> > to create that sucker and we won't be going through the connect()
>> > at all.
>>
>> In the case Dmitry reported, unix_dgram_sendmsg() calls unix_autobind(),
>> not SOCK_STREAM.
>
> Yes, I've noticed. What I'm asking is what in there needs autobind triggered
> on sendmsg and why doesn't the same need affect the SOCK_STREAM case?
With respect to the conditionality on SOCK_PASSCRED those are the linux
semantics. Semantically that is the way the code has behaved since
2.1.15 when support for passing credentials was added to the code.
So I presume someone thought it was a good idea to have a name for
a socket that is sending credentials to another socket. It certainly
seems reasonable at first glance.
With socketpair the only path that doesn't enforce this with
SOCK_STREAM and SOCK_PASSCRED that is either an oversight or a don't
care because we already know who is at the other end.
I can imagine two possible fixes:
1) Declare that splice is non-sense in the presence of SOCK_PASSCRED.
2) Someone adds a preparation operation that can be called on
af_unix sockets that will ensure the autobind happens before
any problematic locks are taken.
Eric
next prev parent reply other threads:[~2017-01-17 8:12 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
2017-02-10 1:37 ` Cong Wang
2017-01-17 8:07 ` Eric W. Biederman [this message]
[not found] ` <065031f0-27c5-443d-82f9-2f475fcef8c3@googlegroups.com>
2017-06-23 16:30 ` Cong Wang
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