linux-kernel - Re: [PATCH v4] netlink: Fix autobind race condition that leads to zero port ID

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Message-Id: <20150920.231104.525285577747035896.davem@davemloft.net>
Date:	Sun, 20 Sep 2015 23:11:04 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	tj@...nel.org, cwang@...pensource.com, tom@...bertland.com,
	kafai@...com, kernel-team@...com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, torvalds@...ux-foundation.org,
	jiri@...nulli.us, nicolas.dichtel@...nd.com, tgraf@...g.ch,
	sfeldma@...il.com
Subject: Re: [PATCH v4] netlink: Fix autobind race condition that leads to
 zero port ID

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Mon, 21 Sep 2015 14:06:36 +0800

> On Sun, Sep 20, 2015 at 10:55:21PM -0700, David Miller wrote:
>> From: Herbert Xu <herbert@...dor.apana.org.au>
>> Date: Fri, 18 Sep 2015 19:16:50 +0800
>> 
>> > The commit c0bb07df7d981e4091432754e30c9c720e2c0c78 ("netlink:
>> > Reset portid after netlink_insert failure") introduced a race
>> > condition where if two threads try to autobind the same socket
>> > one of them may end up with a zero port ID.  This led to kernel
>> > deadlocks that were observed by multiple people.
>> > 
>> > This patch reverts that commit and instead fixes it by introducing
>> > a separte rhash_portid variable so that the real portid is only set
>> > after the socket has been successfully hashed.
>> > 
>> > Fixes: c0bb07df7d98 ("netlink: Reset portid after netlink_insert failure")
>> > Reported-by: Tejun Heo <tj@...nel.org>
>> > Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
>> > Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
>> 
>> Applied and queued up for -stable, thanks Herbert.
> 
> Sorry but Dave but there are still races with v4 as Tejun pointed
> out.  I'm still working on it and I could post them as incremental
> patches if that's the easiest.

Oops, sorry about that.

Yeah at this point incremental patches work the best.

Thanks.
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