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

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 4/10/2015 10:54 AM, Johannes Berg wrote:

> From: Johannes Berg <johannes.berg@intel.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@intel.com>
> ---
>   Documentation/networking/ip-sysctl.txt | 6 ++++++
>   include/uapi/linux/ip.h                | 1 +
>   net/ipv4/arp.c                         | 8 ++++++++
>   net/ipv4/devinet.c                     | 2 ++
>   4 files changed, 17 insertions(+)

[...]
> 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.
> +  */

    Hm, why this strange indentation?

> +	if (IN_DEV_CONF_GET(in_dev, DROP_GRATUITOUS_ARP) && sip == tip)
> +		goto out;
> +
>   /*
>    *     Special case: We must set Frame Relay source Q.922 address
>    */
[...]

WBR, Sergei