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

From: Herbert Xu <herbert@gondor.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:

quoted

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Fri, 18 Sep 2015 19:16:50 +0800

quoted

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@kernel.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.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.