[RFC] mac80211: disallow bridging managed/adhoc interfaces

[RFC] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

A number of people have tried to add a wireless interface
(in managed mode) to a bridge and then complained that it
doesn't work. It cannot work, however, because in 802.11
networks all packets need to be acknowledged and as such
need to be sent to the right address. Promiscuous doesn't
help here. The wireless address format used for these
links has only space for three addresses, the
 * transmitter, which must be equal to the sender (origin)
 * receiver (on the wireless medium), which is the AP in
   the case of managed mode
 * the recipient (destination), which is on the APs local
   network segment

In an IBSS, it is similar, but the receiver and recipient
must match and the third address is used as the BSSID.

To avoid such mistakes in the future, disallow adding a
wireless interface to a bridge.

Felix has recently added a four-address mode to the AP
and client side that can be used (after negotiating that
it is possible, which must happen out-of-band by setting
up both sides) for bridging, so allow that case.

Signed-off-by: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
---
 include/linux/if.h   |    1 +
 net/bridge/br_if.c   |    4 ++++
 net/mac80211/cfg.c   |    9 ++++++++-
 net/mac80211/iface.c |   17 +++++++++++++++--
 4 files changed, 28 insertions(+), 3 deletions(-)

--- wireless-testing.orig/include/linux/if.h	2009-11-17 14:18:36.000000000 +0100
+++ wireless-testing/include/linux/if.h	2009-11-17 14:19:04.000000000 +0100
@@ -70,6 +70,7 @@
 #define IFF_XMIT_DST_RELEASE 0x400	/* dev_hard_start_xmit() is allowed to
 					 * release skb->dst
 					 */
+#define IFF_DONT_BRIDGE 0x800		/* disallow bridging this ether dev */
 
 #define IF_GET_IFACE	0x0001		/* for querying only */
 #define IF_GET_PROTO	0x0002
--- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
+++ wireless-testing/net/bridge/br_if.c	2009-11-17 14:20:03.000000000 +0100
@@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
 	if (dev->br_port != NULL)
 		return -EBUSY;
 
+	/* No bridging devices that dislike that (e.g. wireless) */
+	if (dev->priv_flags & IFF_DONT_BRIDGE)
+		return -EINVAL;
+
 	p = new_nbp(br, dev);
 	if (IS_ERR(p))
 		return PTR_ERR(p);
--- wireless-testing.orig/net/mac80211/cfg.c	2009-11-17 14:21:24.000000000 +0100
+++ wireless-testing/net/mac80211/cfg.c	2009-11-17 14:37:13.000000000 +0100
@@ -106,8 +106,15 @@ static int ieee80211_change_iface(struct
 					    params->mesh_id_len,
 					    params->mesh_id);
 
-	if (params->use_4addr >= 0)
+	if (params->use_4addr >= 0) {
 		sdata->use_4addr = !!params->use_4addr;
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+
+		if ((sdata->vif.type == NL80211_IFTYPE_STATION ||
+		     sdata->vif.type == NL80211_IFTYPE_ADHOC) &&
+		    !sdata->use_4addr)
+			sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	}
 
 	if (sdata->vif.type != NL80211_IFTYPE_MONITOR || !flags)
 		return 0;
--- wireless-testing.orig/net/mac80211/iface.c	2009-11-17 14:20:19.000000000 +0100
+++ wireless-testing/net/mac80211/iface.c	2009-11-17 14:33:25.000000000 +0100
@@ -769,6 +769,11 @@ int ieee80211_if_change_type(struct ieee
 			sdata->local->hw.conf.channel->band);
 	sdata->drop_unencrypted = 0;
 	sdata->use_4addr = 0;
+	if (sdata->vif.type == NL80211_IFTYPE_STATION ||
+	    sdata->vif.type == NL80211_IFTYPE_ADHOC)
+		sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	else
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
 
 	return 0;
 }
@@ -843,8 +848,16 @@ int ieee80211_if_add(struct ieee80211_lo
 					    params->mesh_id_len,
 					    params->mesh_id);
 
-	if (params && params->use_4addr >= 0)
-		sdata->use_4addr = !!params->use_4addr;
+	if (sdata->vif.type == NL80211_IFTYPE_STATION ||
+	    sdata->vif.type == NL80211_IFTYPE_ADHOC)
+		sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	else
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+
+	if (params && params->use_4addr > 0) {
+		sdata->use_4addr = true;
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+	}
 
 	mutex_lock(&local->iflist_mtx);
 	list_add_tail_rcu(&sdata->list, &local->interfaces);


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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[John W. Linville]

On Tue, Nov 17, 2009 at 02:46:25PM +0100, Johannes Berg wrote:
> A number of people have tried to add a wireless interface
> (in managed mode) to a bridge and then complained that it
> doesn't work. It cannot work, however, because in 802.11
> networks all packets need to be acknowledged and as such
> need to be sent to the right address. Promiscuous doesn't
> help here. The wireless address format used for these
> links has only space for three addresses, the
>  * transmitter, which must be equal to the sender (origin)
>  * receiver (on the wireless medium), which is the AP in
>    the case of managed mode
>  * the recipient (destination), which is on the APs local
>    network segment
> 
> In an IBSS, it is similar, but the receiver and recipient
> must match and the third address is used as the BSSID.
> 
> To avoid such mistakes in the future, disallow adding a
> wireless interface to a bridge.
> 
> Felix has recently added a four-address mode to the AP
> and client side that can be used (after negotiating that
> it is possible, which must happen out-of-band by setting
> up both sides) for bridging, so allow that case.
> 
> Signed-off-by: Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>

ACK -- we get these complaints fairly often...

I don't think I've sent the 4addr stuff to Dave yet.  Should I just
take this through my tree?

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org			might be all we have.  Be ready.
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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 08:58 -0500, John W. Linville wrote:

> > To avoid such mistakes in the future, disallow adding a
> > wireless interface to a bridge.
> > 
> > Felix has recently added a four-address mode to the AP
> > and client side that can be used (after negotiating that
> > it is possible, which must happen out-of-band by setting
> > up both sides) for bridging, so allow that case.
> > 
> > Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
> 
> ACK -- we get these complaints fairly often...
> 
> I don't think I've sent the 4addr stuff to Dave yet.  Should I just
> take this through my tree?

After ack from Stephen maybe?

johannes

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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Michael Buesch]

On Tuesday 17 November 2009 14:46:25 Johannes Berg wrote:
> --- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
> +++ wireless-testing/net/bridge/br_if.c	2009-11-17 14:20:03.000000000 +0100
> @@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
>  	if (dev->br_port != NULL)
>  		return -EBUSY;
>  
> +	/* No bridging devices that dislike that (e.g. wireless) */
> +	if (dev->priv_flags & IFF_DONT_BRIDGE)
> +		return -EINVAL;

-EOPNOTSUPP?
That would probably produce a better error message in userspace.

-- 
Greetings, Michael.

Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[John W. Linville]

On Tue, Nov 17, 2009 at 03:04:52PM +0100, Michael Buesch wrote:
> On Tuesday 17 November 2009 14:46:25 Johannes Berg wrote:
> > --- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
> > +++ wireless-testing/net/bridge/br_if.c	2009-11-17 14:20:03.000000000 +0100
> > @@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
> >  	if (dev->br_port != NULL)
> >  		return -EBUSY;
> >  
> > +	/* No bridging devices that dislike that (e.g. wireless) */
> > +	if (dev->priv_flags & IFF_DONT_BRIDGE)
> > +		return -EINVAL;
> 
> -EOPNOTSUPP?
> That would probably produce a better error message in userspace.

Yes, good point.

-- 
John W. Linville		Someday the world will need a hero, and you
linville-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org			might be all we have.  Be ready.
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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 15:04 +0100, Michael Buesch wrote:
> On Tuesday 17 November 2009 14:46:25 Johannes Berg wrote:
> > --- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
> > +++ wireless-testing/net/bridge/br_if.c	2009-11-17 14:20:03.000000000 +0100
> > @@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
> >  	if (dev->br_port != NULL)
> >  		return -EBUSY;
> >  
> > +	/* No bridging devices that dislike that (e.g. wireless) */
> > +	if (dev->priv_flags & IFF_DONT_BRIDGE)
> > +		return -EINVAL;
> 
> -EOPNOTSUPP?
> That would probably produce a better error message in userspace.

Good idea, will wait a bit for other comments and fix this when I send
as [PATCH].

johannes

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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Stephen Hemminger]

On Tue, 17 Nov 2009 15:07:48 +0100
Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> wrote:

> On Tue, 2009-11-17 at 15:04 +0100, Michael Buesch wrote:
> > On Tuesday 17 November 2009 14:46:25 Johannes Berg wrote:
> > > --- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
> > > +++ wireless-testing/net/bridge/br_if.c	2009-11-17 14:20:03.000000000 +0100
> > > @@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
> > >  	if (dev->br_port != NULL)
> > >  		return -EBUSY;
> > >  
> > > +	/* No bridging devices that dislike that (e.g. wireless) */
> > > +	if (dev->priv_flags & IFF_DONT_BRIDGE)
> > > +		return -EINVAL;
> > 
> > -EOPNOTSUPP?
> > That would probably produce a better error message in userspace.

But there are people bridging wireless, and hostap even has a mode for
that. Especially people are bridging to wireless when the other interfaces
are VMs.

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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 08:37 -0800, Stephen Hemminger wrote:

> But there are people bridging wireless, and hostap even has a mode for
> that. 

But that's the AP side, which this patch doesn't attempt to prevent. It
just makes no sense to bridge when connected to an AP or part of an
IBSS.

johannes

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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Stephen Hemminger]

On Tue, 17 Nov 2009 17:43:43 +0100
Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> wrote:

> On Tue, 2009-11-17 at 08:37 -0800, Stephen Hemminger wrote:
> 
> > But there are people bridging wireless, and hostap even has a mode for
> > that. 
> 
> But that's the AP side, which this patch doesn't attempt to prevent. It
> just makes no sense to bridge when connected to an AP or part of an
> IBSS.
> 

Then how does this work now? And will your change break it?

                             kvm1
                            /
     ====> wlan0  --- bridge-- kvm2
                            \
                             kvm3
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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 09:04 -0800, Stephen Hemminger wrote:

> Then how does this work now? And will your change break it?
> 
>                              kvm1
>                             /
>      ====> wlan0  --- bridge-- kvm2
>                             \
>                              kvm3

What's the type of wlan0? If it's managed, i.e. connected to an AP,
it /doesn't/ actually work now, which is my point.

johannes

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Re: [RFC] mac80211: disallow bridging managed/adhoc interfaces

[Dan Williams]

On Tue, 2009-11-17 at 09:04 -0800, Stephen Hemminger wrote:
> On Tue, 17 Nov 2009 17:43:43 +0100
> Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> wrote:
> 
> > On Tue, 2009-11-17 at 08:37 -0800, Stephen Hemminger wrote:
> > 
> > > But there are people bridging wireless, and hostap even has a mode for
> > > that. 
> > 
> > But that's the AP side, which this patch doesn't attempt to prevent. It
> > just makes no sense to bridge when connected to an AP or part of an
> > IBSS.
> > 
> 
> Then how does this work now? And will your change break it?
> 
>                              kvm1
>                             /
>      ====> wlan0  --- bridge-- kvm2
>                             \
>                              kvm3

Are you sure 'bridge' isn't NAT-ed to wlan0 like libvirt/etc do by
default?  That's about the only way it can possibly work correctly with
wifi.

Dan


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[RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

A number of people have tried to add a wireless interface
(in managed mode) to a bridge and then complained that it
doesn't work. It cannot work, however, because in 802.11
networks all packets need to be acknowledged and as such
need to be sent to the right address. Promiscuous doesn't
help here. The wireless address format used for these
links has only space for three addresses, the
 * transmitter, which must be equal to the sender (origin)
 * receiver (on the wireless medium), which is the AP in
   the case of managed mode
 * the recipient (destination), which is on the APs local
   network segment

In an IBSS, it is similar, but the receiver and recipient
must match and the third address is used as the BSSID.

To avoid such mistakes in the future, disallow adding a
wireless interface to a bridge.

Felix has recently added a four-address mode to the AP
and client side that can be used (after negotiating that
it is possible, which must happen out-of-band by setting
up both sides) for bridging, so allow that case.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
---
v2: * change error code as requested by Michael
    * disallow changing wireless mode on a bridged iface

Should more (all?) of this be in cfg80211?

 include/linux/if.h   |    1 +
 net/bridge/br_if.c   |    4 ++++
 net/mac80211/cfg.c   |    9 ++++++++-
 net/mac80211/iface.c |   22 ++++++++++++++++++++--
 4 files changed, 33 insertions(+), 3 deletions(-)

--- wireless-testing.orig/include/linux/if.h	2009-11-17 14:18:36.000000000 +0100
+++ wireless-testing/include/linux/if.h	2009-11-17 14:19:04.000000000 +0100
@@ -70,6 +70,7 @@
 #define IFF_XMIT_DST_RELEASE 0x400	/* dev_hard_start_xmit() is allowed to
 					 * release skb->dst
 					 */
+#define IFF_DONT_BRIDGE 0x800		/* disallow bridging this ether dev */
 
 #define IF_GET_IFACE	0x0001		/* for querying only */
 #define IF_GET_PROTO	0x0002
--- wireless-testing.orig/net/bridge/br_if.c	2009-11-17 14:19:17.000000000 +0100
+++ wireless-testing/net/bridge/br_if.c	2009-11-17 15:07:59.000000000 +0100
@@ -390,6 +390,10 @@ int br_add_if(struct net_bridge *br, str
 	if (dev->br_port != NULL)
 		return -EBUSY;
 
+	/* No bridging devices that dislike that (e.g. wireless) */
+	if (dev->priv_flags & IFF_DONT_BRIDGE)
+		return -EOPNOTSUPP;
+
 	p = new_nbp(br, dev);
 	if (IS_ERR(p))
 		return PTR_ERR(p);
--- wireless-testing.orig/net/mac80211/cfg.c	2009-11-17 14:21:24.000000000 +0100
+++ wireless-testing/net/mac80211/cfg.c	2009-11-17 14:37:13.000000000 +0100
@@ -106,8 +106,15 @@ static int ieee80211_change_iface(struct
 					    params->mesh_id_len,
 					    params->mesh_id);
 
-	if (params->use_4addr >= 0)
+	if (params->use_4addr >= 0) {
 		sdata->use_4addr = !!params->use_4addr;
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+
+		if ((sdata->vif.type == NL80211_IFTYPE_STATION ||
+		     sdata->vif.type == NL80211_IFTYPE_ADHOC) &&
+		    !sdata->use_4addr)
+			sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	}
 
 	if (sdata->vif.type != NL80211_IFTYPE_MONITOR || !flags)
 		return 0;
--- wireless-testing.orig/net/mac80211/iface.c	2009-11-17 14:20:19.000000000 +0100
+++ wireless-testing/net/mac80211/iface.c	2009-11-17 17:56:08.000000000 +0100
@@ -745,6 +745,11 @@ int ieee80211_if_change_type(struct ieee
 	if (type == sdata->vif.type)
 		return 0;
 
+	/* if it's part of a bridge, reject changing type to station/ibss */
+	if (sdata->dev->br_port && (type == NL80211_IFTYPE_ADHOC ||
+				    type == NL80211_IFTYPE_STATION))
+		return -EBUSY;
+
 	/* Setting ad-hoc mode on non-IBSS channel is not supported. */
 	if (sdata->local->oper_channel->flags & IEEE80211_CHAN_NO_IBSS &&
 	    type == NL80211_IFTYPE_ADHOC)
@@ -769,6 +774,11 @@ int ieee80211_if_change_type(struct ieee
 			sdata->local->hw.conf.channel->band);
 	sdata->drop_unencrypted = 0;
 	sdata->use_4addr = 0;
+	if (sdata->vif.type == NL80211_IFTYPE_STATION ||
+	    sdata->vif.type == NL80211_IFTYPE_ADHOC)
+		sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	else
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
 
 	return 0;
 }
@@ -843,8 +853,16 @@ int ieee80211_if_add(struct ieee80211_lo
 					    params->mesh_id_len,
 					    params->mesh_id);
 
-	if (params && params->use_4addr >= 0)
-		sdata->use_4addr = !!params->use_4addr;
+	if (sdata->vif.type == NL80211_IFTYPE_STATION ||
+	    sdata->vif.type == NL80211_IFTYPE_ADHOC)
+		sdata->dev->priv_flags |= IFF_DONT_BRIDGE;
+	else
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+
+	if (params && params->use_4addr > 0) {
+		sdata->use_4addr = true;
+		sdata->dev->priv_flags &= ~IFF_DONT_BRIDGE;
+	}
 
 	mutex_lock(&local->iflist_mtx);
 	list_add_tail_rcu(&sdata->list, &local->interfaces);

Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Julian Calaby]

On Wed, Nov 18, 2009 at 07:48, Johannes Berg <johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> wrote:
> --- wireless-testing.orig/net/mac80211/iface.c  2009-11-17 14:20:19.000000000 +0100
> +++ wireless-testing/net/mac80211/iface.c       2009-11-17 17:56:08.000000000 +0100
> @@ -745,6 +745,11 @@ int ieee80211_if_change_type(struct ieee
>        if (type == sdata->vif.type)
>                return 0;
>
> +       /* if it's part of a bridge, reject changing type to station/ibss */
> +       if (sdata->dev->br_port && (type == NL80211_IFTYPE_ADHOC ||
> +                                   type == NL80211_IFTYPE_STATION))
> +               return -EBUSY;

Busy doesn't seem like the right error here ... maybe use -EOPNOTSUPP
like the next test?

Thanks,

-- 

Julian Calaby

Email: julian.calaby-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
.Plan: http://sites.google.com/site/juliancalaby/
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Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

[-- Attachment #1: Type: text/plain, Size: 1090 bytes --]

On Wed, 2009-11-18 at 09:42 +1100, Julian Calaby wrote:
> On Wed, Nov 18, 2009 at 07:48, Johannes Berg <johannes@sipsolutions.net> wrote:
> > --- wireless-testing.orig/net/mac80211/iface.c  2009-11-17 14:20:19.000000000 +0100
> > +++ wireless-testing/net/mac80211/iface.c       2009-11-17 17:56:08.000000000 +0100
> > @@ -745,6 +745,11 @@ int ieee80211_if_change_type(struct ieee
> >        if (type == sdata->vif.type)
> >                return 0;
> >
> > +       /* if it's part of a bridge, reject changing type to station/ibss */
> > +       if (sdata->dev->br_port && (type == NL80211_IFTYPE_ADHOC ||
> > +                                   type == NL80211_IFTYPE_STATION))
> > +               return -EBUSY;
> 
> Busy doesn't seem like the right error here ... maybe use -EOPNOTSUPP
> like the next test?

Not sure, it's a temporary error and you can fix it by removing it from
the bridge, so it's "busy" in the sense that it is fixed to the current
mode or any other bridging mode by being in the bridge ... it's not that
it doesn't support the mode.

johannes

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Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Julian Calaby]

On Wed, Nov 18, 2009 at 09:46, Johannes Berg <johannes@sipsolutions.net> wrote:
> On Wed, 2009-11-18 at 09:42 +1100, Julian Calaby wrote:
>> On Wed, Nov 18, 2009 at 07:48, Johannes Berg <johannes@sipsolutions.net> wrote:
>> > --- wireless-testing.orig/net/mac80211/iface.c  2009-11-17 14:20:19.000000000 +0100
>> > +++ wireless-testing/net/mac80211/iface.c       2009-11-17 17:56:08.000000000 +0100
>> > @@ -745,6 +745,11 @@ int ieee80211_if_change_type(struct ieee
>> >        if (type == sdata->vif.type)
>> >                return 0;
>> >
>> > +       /* if it's part of a bridge, reject changing type to station/ibss */
>> > +       if (sdata->dev->br_port && (type == NL80211_IFTYPE_ADHOC ||
>> > +                                   type == NL80211_IFTYPE_STATION))
>> > +               return -EBUSY;
>>
>> Busy doesn't seem like the right error here ... maybe use -EOPNOTSUPP
>> like the next test?
>
> Not sure, it's a temporary error and you can fix it by removing it from
> the bridge, so it's "busy" in the sense that it is fixed to the current
> mode or any other bridging mode by being in the bridge ... it's not that
> it doesn't support the mode.

Arguably the test following this (ensuring that we don't set ad-hoc
mode on a non-ad-hoc channel) is equally temporary - i.e. both actions
require the user to do something before they'll work again.

But then, the test after that - for whether the interface is running -
returns -EBUSY - and is just as easy to remedy, so........

Thanks,

-- 

Julian Calaby

Email: julian.calaby@gmail.com
.Plan: http://sites.google.com/site/juliancalaby/

Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Stephen Hemminger]

On Tue, 17 Nov 2009 21:48:18 +0100
Johannes Berg <johannes@sipsolutions.net> wrote:

> A number of people have tried to add a wireless interface
> (in managed mode) to a bridge and then complained that it
> doesn't work. It cannot work, however, because in 802.11
> networks all packets need to be acknowledged and as such
> need to be sent to the right address. Promiscuous doesn't
> help here. The wireless address format used for these
> links has only space for three addresses, the
>  * transmitter, which must be equal to the sender (origin)
>  * receiver (on the wireless medium), which is the AP in
>    the case of managed mode
>  * the recipient (destination), which is on the APs local
>    network segment
> 
> In an IBSS, it is similar, but the receiver and recipient
> must match and the third address is used as the BSSID.
> 
> To avoid such mistakes in the future, disallow adding a
> wireless interface to a bridge.
> 
> Felix has recently added a four-address mode to the AP
> and client side that can be used (after negotiating that
> it is possible, which must happen out-of-band by setting
> up both sides) for bridging, so allow that case.
> 
> Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

Looks good, maybe true four-address mode support will be available
more widely, and this will no longer be an issue.

Acked-by: Stephen Hemminger <shemminger@vyatta.com>

Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 14:42 -0800, Stephen Hemminger wrote:

> > Felix has recently added a four-address mode to the AP
> > and client side that can be used (after negotiating that
> > it is possible, which must happen out-of-band by setting
> > up both sides) for bridging, so allow that case.

> Looks good, maybe true four-address mode support will be available
> more widely, and this will no longer be an issue.

Doubt it, it breaks the current 802.11 standard, and I think 802.1X too
if you use WPA/RSN. Anyway, thanks.

I'll take a look tomorrow if we can do this generically in cfg80211, and
then send a [PATCH] either way.

johannes

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Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Stefan Monnier]

> A number of people have tried to add a wireless interface
> (in managed mode) to a bridge and then complained that it
> doesn't work. It cannot work, however, because in 802.11
[...]
> To avoid such mistakes in the future, disallow adding a
> wireless interface to a bridge.

As someone who's been bitten by this, I fully support this change.
Still, it makes me wonder: my broadcom-based home-router using the wl.o
driver can be set in "client bridge" mode.  How does it work?


        Stefan

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Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[John W. Linville]

On Tue, Nov 17, 2009 at 08:59:03PM -0500, Stefan Monnier wrote:
> > A number of people have tried to add a wireless interface
> > (in managed mode) to a bridge and then complained that it
> > doesn't work. It cannot work, however, because in 802.11
> [...]
> > To avoid such mistakes in the future, disallow adding a
> > wireless interface to a bridge.
> 
> As someone who's been bitten by this, I fully support this change.
> Still, it makes me wonder: my broadcom-based home-router using the wl.o
> driver can be set in "client bridge" mode.  How does it work?

If I'm not mistaken, that has a bunch of code embedded in it that
among other things can do a layer-2 version of NAT to rewrite the
MAC adresses for frames on the air.

YMMV...

John
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Re: [RFC v2] mac80211: disallow bridging managed/adhoc interfaces

[Johannes Berg]

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On Tue, 2009-11-17 at 21:59 -0500, John W. Linville wrote:

> > As someone who's been bitten by this, I fully support this change.
> > Still, it makes me wonder: my broadcom-based home-router using the wl.o
> > driver can be set in "client bridge" mode.  How does it work?
> 
> If I'm not mistaken, that has a bunch of code embedded in it that
> among other things can do a layer-2 version of NAT to rewrite the
> MAC adresses for frames on the air.

Yeah, that's how it works. You can probably achieve the same effect with
the ebtable_nat module in ebtables but I've never even attempted to try
that.

johannes

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