linux-kernel - Re: [NETLINK] Don't attach callback to a going-away netlink socket

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Message-ID: <4625DEFC.7040701@sw.ru>
Date:	Wed, 18 Apr 2007 13:03:56 +0400
From:	Pavel Emelianov <xemul@...ru>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
CC:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org, Patrick McHardy <kaber@...sh.net>,
	Kirill Korotaev <dev@...nvz.org>
Subject: Re: [NETLINK] Don't attach callback to a going-away netlink socket

Evgeniy Polyakov wrote:
> On Wed, Apr 18, 2007 at 12:32:40PM +0400, Pavel Emelianov (xemul@...ru) wrote:
>> Evgeniy Polyakov wrote:
>>> On Wed, Apr 18, 2007 at 12:16:18PM +0400, Pavel Emelianov (xemul@...ru) wrote:
>>>> Sorry, I forgot to put netdev and David in Cc when I first sent it.
>>>>
>>>> There is a race between netlink_dump_start() and netlink_release()
>>>> that can lead to the situation when a netlink socket with non-zero
>>>> callback is freed.
>>> Out of curiosity, why not to fix a netlink_dump_start() to remove
>>> callback in error path, since in 'no-error' path it removes it in
>> Error path is not relevant here. The problem is that we
>> keep a calback on a socket that is about to be freed.
> 
> Yes, you are right, that it will not be freed in netlink_release(), 
> but it will be freed in netlink_dump() after it is processed (in no-error 
> path only though).
> 

But error path will leak it. On success path we would have
a leaked packet in sk_write_queue, since we did't see it in
skb_queue_purge() while doing netlink_release().

Of course we can place the struts in code to handle the case
when we have a released socket with the attached callback, but
it is more correct (IMHO) not to allow to attach the callbacks
to dead sockets.
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