linux-kernel - Re: [PATCH] bridge: multicast: add sanity check for query source addresses

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Message-ID: <20140304090614.GA3952@order.stressinduktion.org>
Date:	Tue, 4 Mar 2014 10:06:14 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Linus Lüssing <linus.luessing@....de>
Cc:	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	Stephen Hemminger <stephen@...workplumber.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, Jan Stancek <jstancek@...hat.com>,
	Florian Westphal <fwestpha@...hat.com>
Subject: Re: [PATCH] bridge: multicast: add sanity check for query source addresses

On Tue, Mar 04, 2014 at 03:57:35AM +0100, Linus Lüssing wrote:
> MLD queries are supposed to have an IPv6 link-local source address
> according to RFC2710, section 4 and RFC3810, section 5.1.14. This patch
> adds a sanity check to ignore such broken MLD queries.
> 
> Without this check, such malformed MLD queries can result in a
> denial of service: The queries are ignored by any MLD listener
> therefore they will not respond with an MLD report. However,
> without this patch these malformed MLD queries would enable the
> snooping part in the bridge code, potentially shutting down the
> according ports towards these hosts for multicast traffic as the
> bridge did not learn about these listeners.
> 
> Reported-by: Jan Stancek <jstancek@...hat.com>
> Signed-off-by: Linus Lüssing <linus.luessing@....de>
> ---
>  net/bridge/br_multicast.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index ef66365..fb0e36f 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -1235,6 +1235,12 @@ static int br_ip6_multicast_query(struct net_bridge *br,
>  	    (port && port->state == BR_STATE_DISABLED))
>  		goto out;
>  
> +	/* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
> +	if (!(ipv6_addr_type(&ip6h->saddr) & IPV6_ADDR_LINKLOCAL)) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +

Shouldn't we allow empty source address, here?

Routers are supposed to drop them but bridges care. Linux uses ::
as source address as long as no valid LL addresses are available,
e.g. at boot-up (RFC3810 5.2.13.).

Greetings,

  Hannes

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