netdev - Re: [PATCH net] netlink: make sure -EBUSY won't escape from netlink

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Message-ID: <20150917054114.GN1983@Chimay.local>
Date:	Wed, 16 Sep 2015 22:41:14 -0700
From:	Christoph Paasch <christoph.paasch@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	daniel@...earbox.net, herbert@...dor.apana.org.au, tgraf@...g.ch,
	torvalds@...ux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] netlink: make sure -EBUSY won't escape from
 netlink_insert

Hello,

On 10/08/15 - 11:00:15, David Miller wrote:
> From: Daniel Borkmann <daniel@...earbox.net>
> Date: Fri,  7 Aug 2015 00:26:41 +0200
> > Linus reports the following deadlock on rtnl_mutex; triggered only
> > once so far (extract):
>  ...
> > It seems so far plausible that the recursive call into rtnetlink_rcv()
> > looks suspicious. One way, where this could trigger is that the senders
> > NETLINK_CB(skb).portid was wrongly 0 (which is rtnetlink socket), so
> > the rtnl_getlink() request's answer would be sent to the kernel instead
> > to the actual user process, thus grabbing rtnl_mutex() twice.
> > 
> > One theory would be that netlink_autobind() triggered via netlink_sendmsg()
> > internally overwrites the -EBUSY error to 0, but where it is wrongly
> > originating from __netlink_insert() instead. That would reset the
> > socket's portid to 0, which is then filled into NETLINK_CB(skb).portid
> > later on. As commit d470e3b483dc ("[NETLINK]: Fix two socket hashing bugs.")
> > also puts it, -EBUSY should not be propagated from netlink_insert().
> > 
> > It looks like it's very unlikely to reproduce. We need to trigger the
> > rhashtable_insert_rehash() handler under a situation where rehashing
> > currently occurs (one /rare/ way would be to hit ht->elasticity limits
> > while not filled enough to expand the hashtable, but that would rather
> > require a specifically crafted bind() sequence with knowledge about
> > destination slots, seems unlikely). It probably makes sense to guard
> > __netlink_insert() in any case and remap that error. It was suggested
> > that EOVERFLOW might be better than an already overloaded ENOMEM.
> > 
> > Reference: http://thread.gmane.org/gmane.linux.network/372676
> > Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> 
> Applied and queued up for -stable, thanks.

can this patch get queued up for 4.1 as well?
It seems to fix a similar issue in 4.1.6.


Thanks,
Christoph

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