netdev - Re: [PATCH] bridge: Forward EAPOL Kconfig option BRIDGE_PAE

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Date:	Tue, 28 Jun 2011 08:10:15 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Lamparter <equinox@...c24.net>
Cc:	Nick Carter <ncarter100@...il.com>, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [PATCH] bridge: Forward EAPOL Kconfig option BRIDGE_PAE_FORWARD

On Tue, 28 Jun 2011 17:02:57 +0200
David Lamparter <equinox@...c24.net> wrote:

> On Sat, Jun 25, 2011 at 12:33:05AM +0100, Nick Carter wrote:
> > @@ -98,6 +98,14 @@ int br_handle_frame_finish(struct sk_buff *skb)
> >  	}
> > 
> >  	if (skb) {
> > +		/* Prevent Crosstalk where a Supplicant on one Port attempts to
> > +		 * interfere with authentications occurring on another Port.
> > +		 * (IEEE Std 802.1X-2001 C.3.3)
> > +		 */
> > +		if (unlikely(!br->pae_forward &&
> > +		    skb->protocol == htons(ETH_P_PAE)))
> > +			goto drop;
> > +
> >  		if (dst)
> >  			br_forward(dst->dst, skb, skb2);
> >  		else
> > @@ -166,6 +174,10 @@ struct sk_buff *br_handle_frame(struct sk_buff *skb)
> >  		if (p->br->stp_enabled == BR_NO_STP && dest[5] == 0)
> >  			goto forward;
> > 
> > +		/* Check if PAE frame should be forwarded */
> > +		if (p->br->pae_forward && skb->protocol == htons(ETH_P_PAE))
> > +			goto forward;
> > +
> >  		if (NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, skb, skb->dev,
> >  			    NULL, br_handle_local_finish))
> >  			return NULL;	/* frame consumed by filter */
> 
> No, please don't.
> 
> Linux bridging has two "grand" modes: dumb and STP enabled.
> 
> If we're running a dumb bridge, we behave like an ethernet hub without
> any intelligence, and in that case we should absolutely forward 802.1X
> frames. We may have (e.g. VM) client(s) that want to authenticate with a
> physical switch.
> (For the spec, this counts as "repeater", not "bridge"/"switch")
> 
> If we're running with STP enabled, then 802.1X traffic should already be
> caught by the general ethernet link-local multicast drop (which applies
> to 01:80:c2:/24 and therefore catches 802.1X too.)

The problem is that STP is not enabled by default, and most people don't
know how to enable it.
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