[PATCH] bridge: multicast: add sanity check for query source addresses

[PATCH] bridge: multicast: add sanity check for query source addresses

[Linus Lüssing]

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@redhat.com>
Signed-off-by: Linus Lüssing <linus.luessing@web.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;
+	}
+
 	if (skb->len == sizeof(*mld)) {
 		if (!pskb_may_pull(skb, sizeof(*mld))) {
 			err = -EINVAL;
-- 
1.7.10.4

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

[Hannes Frederic Sowa]

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@redhat.com>
> Signed-off-by: Linus Lüssing <linus.luessing@web.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

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

[Linus Lüssing]

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On Tue, Mar 04, 2014 at 10:06:14AM +0100, Hannes Frederic Sowa wrote:
> > 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.).

RFC3810, 5.2.13. refers to MLD reports, not queries, so that
shouldn't be relevant, section 5.1.14 should apply. Also the
bridge code only issues queries with a valid link-local source
address (see br_ip6_multicast_alloc_query() in
net/bridge/br_multicast.c). Where does Linux use :: for queries?

Cheers, Linus

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

[Hannes Frederic Sowa]

On Tue, Mar 04, 2014 at 11:43:55AM +0100, Linus Lüssing wrote:
> On Tue, Mar 04, 2014 at 10:06:14AM +0100, Hannes Frederic Sowa wrote:
> > > 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.).
> 
> RFC3810, 5.2.13. refers to MLD reports, not queries, so that
> shouldn't be relevant, section 5.1.14 should apply. Also the
> bridge code only issues queries with a valid link-local source
> address (see br_ip6_multicast_alloc_query() in
> net/bridge/br_multicast.c). Where does Linux use :: for queries?

Sorry, I confused queries with reports.
Your patch looks good, same check as in igmp6_event_query.

Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

Bye,

  Hannes

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

[David Miller]

From: Linus Lüssing <linus.luessing@web.de>
Date: Tue,  4 Mar 2014 03:57:35 +0100

> 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@redhat.com>
> Signed-off-by: Linus Lüssing <linus.luessing@web.de>

Applied.