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Date: Wed, 18 Apr 2007 12:42:07 +0400 From: Evgeniy Polyakov <johnpol@....mipt.ru> To: Patrick McHardy <kaber@...sh.net> Cc: Pavel Emelianov <xemul@...ru>, 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, Kirill Korotaev <dev@...nvz.org> Subject: Re: [NETLINK] Don't attach callback to a going-away netlink socket On Wed, Apr 18, 2007 at 10:26:31AM +0200, Patrick McHardy (kaber@...sh.net) 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 > > netlink_dump(). > > > 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? > > And, btw, can release method be called while socket is being used, I > > thought about proper reference counters should prevent this, but not > > 100% sure with RCU dereferencing of the descriptor. > > > 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? -- Evgeniy Polyakov - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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