Subject: Re: [PATCH net] Bridge: Fix ipv6 mc snooping if bridge has no ipv6 address

From: Linus Lüssing <[email-masked]>
Date: Sat, 25 Jun 2016 16:20:28 +0200

On Fri, Jun 24, 2016 at 12:35:18PM +0200, Daniel Danzberger wrote:
> The bridge is falsly dropping ipv6 mulitcast packets if there is:
>  1. No ipv6 address assigned on the brigde.
>  2. No external mld querier present.
>  3. The internal querier enabled.
> 
> When the bridge fails to build mld queries, because it has no
> ipv6 address, it slilently returns, but keeps the local querier enabled.
> This specific case causes confusing packet loss.
> 
> Ipv6 multicast snooping can only work if:
>  a) An external querier is present
>  OR
>  b) The bridge has an ipv6 address an is capable of sending own queries
> 
> Otherwise it has to forward/flood the ipv6 multicast traffic,
> because snooping cannot work.
> 
> This patch fixes the issue by adding a flag to the bridge struct that
> indicates that there is currently no ipv6 address assinged to the bridge
> and returns a false state for the local querier in
> __br_multicast_querier_exists().

Fixes: 1d81d4c3dd88 ("bridge: check return value of ipv6_dev_get_saddr()")