netdev - Re: [PATCH net] netfilter: nf_queue: Don't recompute the hook

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Message-ID: <20150623161709.GA3752@salvia>
Date:	Tue, 23 Jun 2015 18:17:10 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org, Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net] netfilter: nf_queue: Don't recompute the hook_list
 head

On Mon, Jun 22, 2015 at 09:56:37AM -0500, Eric W. Biederman wrote:
> Pablo Neira Ayuso <pablo@...filter.org> writes:
[...]
> > There is no nfnetlink_queue support for the netdev family at this
> > moment, so this can't be triggered unless you use an out of tree
> > module.
> >
> > I have a patch here to add a static key to disable userspace queueing
> > per family using a static key so that part would be basically
> > inactive.
> >
> > But if you really want to see this in 4.1, no problem, please just let
> > me know and I'll pass it to David, as I said it's basically not
> > resolving any urgent problem so this is not harming.
>
> So I have read through the code and I simply do not see anywhere
> that would prevent code in nft_queue to be called on a per netdevice
> chain, or where in nfqnl_enqueue_packet we would decided not to queue
> the packet.
>
> Could you please point me to what in the code makes this code path
> impossible to use?

int nf_queue(struct sk_buff *skb,
             struct nf_hook_ops *elem,
             struct nf_hook_state *state,
             unsigned int queuenum)
{
        const struct nf_afinfo *afinfo;
        ...

        afinfo = nf_get_afinfo(state->pf);
        if (!afinfo)
                goto err_unlock;

        ...
}

There is no afinfo for NFPROTO_NETDEV, so the packet the packet will
be dropped.

Therefore, there is no way nf_reinject() can be called neither for
bridge, arp, inet and netdev at this moment.

I have a patch here to restrict this easily in nft_queue so the user
knows this can't be used at configuration time.
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