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

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

[Jon Maxwell]

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)
+				fdb_notify(br, fdb, RTM_NEWNEIGH);
 			fdb->dst = source;
 			fdb->updated = jiffies;
 			if (unlikely(added_by_user))
-- 
1.8.3.1

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

[Jiri Pirko]

Tue, May 13, 2014 at 09:55:08AM CEST, jmaxwell37@gmail.com 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)
>+				fdb_notify(br, fdb, RTM_NEWNEIGH);
> 			fdb->dst = source;
> 			fdb->updated = jiffies;
> 			if (unlikely(added_by_user))
>-- 
>1.8.3.1


Reviewed-by: Jiri Pirko <jiri@resnulli.us>

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

[Stephen Hemminger]

On Tue, 13 May 2014 17:16:11 +0200
Jiri Pirko <jiri@resnulli.us> wrote:

> Tue, May 13, 2014 at 09:55:08AM CEST, jmaxwell37@gmail.com 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)
> >+				fdb_notify(br, fdb, RTM_NEWNEIGH);
> > 			fdb->dst = source;
> > 			fdb->updated = jiffies;
> > 			if (unlikely(added_by_user))
> >-- 
> >1.8.3.1
> 
> 
> Reviewed-by: Jiri Pirko <jiri@resnulli.us>

I like the patch, but please add unlikely() to this conditional.
This is in the fast path code for bridge learning.

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

[Toshiaki Makita]

(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

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

[Jon Maxwell]

----- Original Message -----
> From: "Toshiaki Makita" <makita.toshiaki@lab.ntt.co.jp>
> To: "Jon Maxwell" <jmaxwell37@gmail.com>, stephen@networkplumber.org
> Cc: davem@davemloft.net, vyasevic@redhat.com, bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
> linux-kernel@vger.kernel.org, jpirko@redhat.com, jmaxwell@redhat.com
> Sent: Wednesday, May 14, 2014 10:34:38 AM
> Subject: Re: [PATCH net] bridge: notify user space of fdb port change
> 
> (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.

It may save a few instructions but I have not tested it.

> 
> > +				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.

It was not on purpose but for this particular case there will be burst of notifies 
so it probably does not matter. However I agree it should be after the update.
I will do that along with adding the unlikely() conditional and resubmit.

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

I would prefer to leave this portion as alone and only use the if 
statement for the notify.

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

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

[Jon Maxwell]

> ----- Original Message -----
> > From: "Toshiaki Makita" <makita.toshiaki@lab.ntt.co.jp>
> > To: "Jon Maxwell" <jmaxwell37@gmail.com>, stephen@networkplumber.org
> > Cc: davem@davemloft.net, vyasevic@redhat.com,
> > bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
> > linux-kernel@vger.kernel.org, jpirko@redhat.com, jmaxwell@redhat.com
> > Sent: Wednesday, May 14, 2014 10:34:38 AM
> > Subject: Re: [PATCH net] bridge: notify user space of fdb port change
> > 
> > (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.
> 
> It may save a few instructions but I have not tested it.
> 
> > 
> > > +				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.
> 
> It was not on purpose but for this particular case there will be burst of
> notifies
> so it probably does not matter. However I agree it should be after the
> update.
> I will do that along with adding the unlikely() conditional and resubmit.
> 
> > 
> > Also, isn't it better to move update of dst into "if" block?
> 
> I would prefer to leave this portion as alone and only use the if
> statement for the notify.
> 
> > 
> > 	if (source != fdb->dst) {
> > 		fdb->dst = source;
> > 		modified = true;
> > 	}
> > 	...
> > 	if (modified) ...
> > 

Makita-san,

I recoded this using your idea and ran it through a reproducer.
It work fine. After some more consideration I agree that 
setting fdb->dst = source is only required when source != fdb->dst.

Thanks for your suggestions. This is the revised patch. It should 
retain the original behaviour except for the notify after the fdb update.  

Please let me know if you have any further input?

$ diff -Naur br_fdb.c br_fdb.c.patch
--- br_fdb.c        2014-05-17 12:43:23.346319609 +1000
+++ br_fdb.c.patch        2014-05-17 16:54:46.280235728 +1000
@@ -487,6 +487,7 @@
 {
         struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
         struct net_bridge_fdb_entry *fdb;
+        bool fdb_modified = 0;
 
         /* some users want to always flood. */
         if (hold_time(br) == 0)
@@ -507,10 +508,16 @@
                                         source->dev->name);
                 } else {
                         /* fastpath: update of existing entry */
-                        fdb->dst = source;
+                        if (unlikely(source != fdb->dst))
+                                {
+                                fdb->dst = source;
+                                fdb_modified = 1;
+                                }
                         fdb->updated = jiffies;
                         if (unlikely(added_by_user))
                                 fdb->added_by_user = 1;
+                        if (unlikely(fdb_modified))
+                                fdb_notify(br, fdb, RTM_NEWNEIGH);
                 }
         } else {
                 spin_lock(&br->hash_lock);


> > Thanks,
> > Toshiaki Makita
> > 
> 

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

[Toshiaki Makita]

(2014/05/23 13:59), Jon Maxwell wrote:
...
> Makita-san,
> 
> I recoded this using your idea and ran it through a reproducer.
> It work fine. After some more consideration I agree that 
> setting fdb->dst = source is only required when source != fdb->dst.
> 
> Thanks for your suggestions. This is the revised patch. It should 
> retain the original behaviour except for the notify after the fdb update.  
> 
> Please let me know if you have any further input?

I have no more comments except for style problems (bracket position,
indentation, type mismatch).
thank you for rewriting :)

Thanks,
Toshiaki Makita

> 
> $ diff -Naur br_fdb.c br_fdb.c.patch
> --- br_fdb.c        2014-05-17 12:43:23.346319609 +1000
> +++ br_fdb.c.patch        2014-05-17 16:54:46.280235728 +1000
> @@ -487,6 +487,7 @@
>  {
>          struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
>          struct net_bridge_fdb_entry *fdb;
> +        bool fdb_modified = 0;
>  
>          /* some users want to always flood. */
>          if (hold_time(br) == 0)
> @@ -507,10 +508,16 @@
>                                          source->dev->name);
>                  } else {
>                          /* fastpath: update of existing entry */
> -                        fdb->dst = source;
> +                        if (unlikely(source != fdb->dst))
> +                                {
> +                                fdb->dst = source;
> +                                fdb_modified = 1;
> +                                }
>                          fdb->updated = jiffies;
>                          if (unlikely(added_by_user))
>                                  fdb->added_by_user = 1;
> +                        if (unlikely(fdb_modified))
> +                                fdb_notify(br, fdb, RTM_NEWNEIGH);
>                  }
>          } else {
>                  spin_lock(&br->hash_lock);
> 
> 

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

[Jon Maxwell]

> I have no more comments except for style problems (bracket position,
> indentation, type mismatch).
> thank you for rewriting :)

np, yes this is a draft but I will make sure complies with checkpatch.pl
before submitting it.

Regards

Jon

> 
> Thanks,
> Toshiaki Makita
> 
> > 
> > $ diff -Naur br_fdb.c br_fdb.c.patch
> > --- br_fdb.c        2014-05-17 12:43:23.346319609 +1000
> > +++ br_fdb.c.patch        2014-05-17 16:54:46.280235728 +1000
> > @@ -487,6 +487,7 @@
> >  {
> >          struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
> >          struct net_bridge_fdb_entry *fdb;
> > +        bool fdb_modified = 0;
> >  
> >          /* some users want to always flood. */
> >          if (hold_time(br) == 0)
> > @@ -507,10 +508,16 @@
> >                                          source->dev->name);
> >                  } else {
> >                          /* fastpath: update of existing entry */
> > -                        fdb->dst = source;
> > +                        if (unlikely(source != fdb->dst))
> > +                                {
> > +                                fdb->dst = source;
> > +                                fdb_modified = 1;
> > +                                }
> >                          fdb->updated = jiffies;
> >                          if (unlikely(added_by_user))
> >                                  fdb->added_by_user = 1;
> > +                        if (unlikely(fdb_modified))
> > +                                fdb_notify(br, fdb, RTM_NEWNEIGH);
> >                  }
> >          } else {
> >                  spin_lock(&br->hash_lock);
> > 
> > 
> 

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

[Jon Maxwell]

----- Original Message -----
> From: "Jon Maxwell" <jmaxwell@redhat.com>
> To: stephen@networkplumber.org
> Cc: davem@davemloft.net, "makita toshiaki" <makita.toshiaki@lab.ntt.co.jp>, vyasevic@redhat.com,
> bridge@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jpirko@redhat.com
> Sent: Friday, May 16, 2014 6:12:51 PM
> Subject: Re: [PATCH net] bridge: notify user space of fdb port change
> 
> Please use this patch. My bad, the previous one
> incorrectly did the notify before fdb->added_by_user = 1.
> 

I just realized I did the port compare after fdb->dst = source;
So the notify will never trigger. It's been a long
day, I'll rewrite this tomorrow and resubmit after 
testing it on my reproducer. Please ignore this one
too.

> ----- Original Message -----
> > From: "Jon Maxwell" <jmaxwell37@gmail.com>
> > To: stephen@networkplumber.org
> > Cc: davem@davemloft.net, "makita toshiaki" <makita.toshiaki@lab.ntt.co.jp>,
> > vyasevic@redhat.com,
> > bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
> > linux-kernel@vger.kernel.org, jpirko@redhat.com,
> > jmaxwell@redhat.com, "Jon Maxwell" <jmaxwell37@gmail.com>
> > Sent: Friday, May 16, 2014 6:08:39 PM
> > Subject: [PATCH net] bridge: notify user space of fdb port change
> > 
> > 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..67480c2 100644
> > --- a/net/bridge/br_fdb.c
> > +++ b/net/bridge/br_fdb.c
> > @@ -511,6 +511,8 @@ void br_fdb_update(struct net_bridge *br, struct
> > net_bridge_port *source,
> >  			fdb->updated = jiffies;
> >  			if (unlikely(added_by_user))
> >  				fdb->added_by_user = 1;
> > +			if (unlikely(source->port_no != fdb->dst->port_no))
> > +				fdb_notify(br, fdb, RTM_NEWNEIGH);
> >  		}
> >  	} else {
> >  		spin_lock(&br->hash_lock);
> > --
> > 1.8.3.1
> > 
> > 
> 

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

[Jon Maxwell]

Please use this patch. My bad, the previous one 
incorrectly did the notify before fdb->added_by_user = 1.

----- Original Message -----
> From: "Jon Maxwell" <jmaxwell37@gmail.com>
> To: stephen@networkplumber.org
> Cc: davem@davemloft.net, "makita toshiaki" <makita.toshiaki@lab.ntt.co.jp>, vyasevic@redhat.com,
> bridge@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jpirko@redhat.com,
> jmaxwell@redhat.com, "Jon Maxwell" <jmaxwell37@gmail.com>
> Sent: Friday, May 16, 2014 6:08:39 PM
> Subject: [PATCH net] bridge: notify user space of fdb port change
> 
> 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..67480c2 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -511,6 +511,8 @@ void br_fdb_update(struct net_bridge *br, struct
> net_bridge_port *source,
>  			fdb->updated = jiffies;
>  			if (unlikely(added_by_user))
>  				fdb->added_by_user = 1;
> +			if (unlikely(source->port_no != fdb->dst->port_no))
> +				fdb_notify(br, fdb, RTM_NEWNEIGH);
>  		}
>  	} else {
>  		spin_lock(&br->hash_lock);
> --
> 1.8.3.1
> 
> 

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

[Jon Maxwell]

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..67480c2 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -511,6 +511,8 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 			fdb->updated = jiffies;
 			if (unlikely(added_by_user))
 				fdb->added_by_user = 1;
+			if (unlikely(source->port_no != fdb->dst->port_no))
+				fdb_notify(br, fdb, RTM_NEWNEIGH);
 		}
 	} else {
 		spin_lock(&br->hash_lock);
-- 
1.8.3.1

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

[Jon Maxwell]

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..c2642f5 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -509,6 +509,8 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 			/* fastpath: update of existing entry */
 			fdb->dst = source;
 			fdb->updated = jiffies;
+			if (unlikely(source->port_no != fdb->dst->port_no))
+				fdb_notify(br, fdb, RTM_NEWNEIGH);
 			if (unlikely(added_by_user))
 				fdb->added_by_user = 1;
 		}
-- 
1.8.3.1