Re: [PATCH net] bridge: notify user space of fdb port change

Toshiaki Makita
2014-05-14T00:34:52Z

(2014/05/13 16:55), Jon Maxwell wrote:
> From: Jon Maxwell <jmaxwell37@gmail.com>
>
> There has been a number incidents recently where customers running KVM have
> reported that VM hosts on different Hypervisors are unreachable. Based on
> pcap traces we found that the bridge was broadcasting the ARP request out
> onto the network. However some NICs have an inbuilt switch which on occasions
> were broadcasting the VMs ARP request back through the physical NIC on the
> Hypervisor. This resulted in the bridge changing ports and incorrectly learning
> that the VMs mac address was external. As a result the ARP reply was directed
> back onto the external network and VM never updated it's ARP cache. This patch
> will notify the bridge command to identify such port toggling.
>
> Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
> ---
> net/bridge/br_fdb.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 9203d5a..37742e2 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -507,6 +507,8 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
> source->dev->name);
> } else {
> /* fastpath: update of existing entry */
> + if (source->port_no != fdb->dst->port_no)

It seems that we don't need to fetch port_no and it is enough to compare
source and fdb->dst.

> + fdb_notify(br, fdb, RTM_NEWNEIGH);
> fdb->dst = source;
> fdb->updated = jiffies;
> if (unlikely(added_by_user))
>

This notifies fdb entry before updating existing entry. Is this on purpose?
I think we should notify the updated fdb entry.
Similar code fdb_add_entry() does after updating it.

Also, isn't it better to move update of dst into "if" block?

if (source != fdb->dst) {
fdb->dst = source;
modified = true;
}
...
if (modified) ...

Thanks,
Toshiaki Makita