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

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Message-ID: <20150921060636.GA30807@gondor.apana.org.au>
Date:	Mon, 21 Sep 2015 14:06:36 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
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

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.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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