netdev - Re: [PATCH 3/4] ipv4: add option to drop gratuitous ARP packets

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Date:	Sat, 11 Apr 2015 13:59:51 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Johannes Berg <johannes@...solutions.net>
cc:	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	matti.gottlieb@...el.com, Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH 3/4] ipv4: add option to drop gratuitous ARP packets


	Hello,

On Fri, 10 Apr 2015, Johannes Berg wrote:

> From: Johannes Berg <johannes.berg@...el.com>
> 
> In certain 802.11 wireless deployments, there will be ARP proxies
> that use knowledge of the network to correctly answer requests.
> To prevent gratuitous ARP frames on the shared medium from being
> a problem, on such deployments wireless needs to drop them.
> 
> Enable this by providing an option called "drop_gratuitous_arp".
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> index 5f5c674e130a..5487d5e5191e 100644
> --- a/net/ipv4/arp.c
> +++ b/net/ipv4/arp.c
> @@ -715,6 +715,14 @@ static int arp_process(struct sk_buff *skb)
>  	    (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip)))
>  		goto out;
>  
> + /*
> +  *	For some 802.11 wireless deployments (and possibly other networks),
> +  *	there will be an ARP proxy and gratuitous ARP frames are attacks
> +  *	and thus should not be accepted.
> +  */
> +	if (IN_DEV_CONF_GET(in_dev, DROP_GRATUITOUS_ARP) && sip == tip)
> +		goto out;

	Does it happen for any pkt_type? IN_DEV_ARP_ACCEPT
is not ON by default, so new entries are not created but
update can happen at any time, even with simple request like
who-has OURIP tell PROXYIP and sha=hacker_mac sent by
attackers. Is that the only gap that needs to be protected
with this patch?

	May be only arptable_filter can help here to
protect ARP?

Regards

--
Julian Anastasov <ja@....bg>
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