From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751570AbXDRJIO (ORCPT ); Wed, 18 Apr 2007 05:08:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751564AbXDRJIO (ORCPT ); Wed, 18 Apr 2007 05:08:14 -0400 Received: from relay.2ka.mipt.ru ([194.85.82.65]:59622 "EHLO 2ka.mipt.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751570AbXDRJIN (ORCPT ); Wed, 18 Apr 2007 05:08:13 -0400 Date: Wed, 18 Apr 2007 13:07:20 +0400 From: Evgeniy Polyakov To: Patrick McHardy Cc: Pavel Emelianov , David Miller , Linux Netdev List , Andrew Morton , Linux Kernel Mailing List , devel@openvz.org, Kirill Korotaev Subject: Re: [NETLINK] Don't attach callback to a going-away netlink socket Message-ID: <20070418090720.GA25070@2ka.mipt.ru> References: <4625D3D2.9030507@sw.ru> <20070418081707.GA29267@2ka.mipt.ru> <4625D637.2040308@trash.net> <20070418084206.GA4241@2ka.mipt.ru> <4625DBE2.5090402@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: <4625DBE2.5090402@trash.net> User-Agent: Mutt/1.5.9i X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (2ka.mipt.ru [0.0.0.0]); Wed, 18 Apr 2007 13:07:28 +0400 (MSD) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 18, 2007 at 10:50:42AM +0200, Patrick McHardy (kaber@trash.net) wrote: > >>It already does (netlink_destroy_callback), but that doesn't help > >>with this race though since without this patch we don't enter the > >>error path. > > > > I thought that with releasing a socket, which will have a callback > > attached only results in a leak of the callback? In that case we can > > just free it in dump() just like it is done in no-error path already. > > Or do I miss something additional? > > That would only work if there is nothing to dump (cb->dump returns 0). > Otherwise it is not freed. That is what I referred to as error path. Btw, with positive return value we end up in subsequent call to input which will free callback under lock as expected. I do not object against the patch, just want to make a clear vision about dumps - if callback is allocated to be used in dump only, then we could just free it there without passing to next round. > >>The problem is asynchronous processing of the dump request in the > >>context of a different process. Process requests a dump, message > >>is queued and process returns from sendmsg since some other process > >>is already processing the queue. Then the process closes the socket, > >>resulting in netlink_release being called. When the dump request > >>is finally processed the race Pavel described might happen. This > >>can only happen for netlink families that use mutex_try_lock for > >>queue processing of course. > > > > > > Doesn't it called from ->sk_data_ready() which is synchronous with > > respect to sendmsg, not sure about conntrack though, but it looks so? > > > Yes, but for kernel sockets we end up calling the input function, > which when mutex_trylock is used returns immediately when some > other process is already processing the queue, so the requesting > process might close the socket before the request is processed. So far it is only netfilter and gennetlink, we would see huge dump from netlink_sock_destruct. Anyway, that is possible situation, thanks for clearing this up. -- Evgeniy Polyakov