Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

Sending with a fixed linux-wireless ML address. Please kindly send your
replies using linux-wireless@

On 02/27/2018 11:08 AM, Rafał Miłecki wrote:
> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
> FullMAC WiFi chipset.
>
>
> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
> 1) IFLA_BRPORT_MCAST_TO_UCAST
> 2) Clients isolation in hostapd
> 3) Hairpin mode enabled
>
> For more details please see Linus's patch description:
> https://patchwork.kernel.org/patch/9530669/
> and maybe hairpin mode patch:
> https://lwn.net/Articles/347344/
>
> Short version: in that setup packets received from a bridged wireless
> interface can be handled back to it for transmission.
>
>
> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
> standard that was replaced by 802.11r.
>
> Whenever a new station associates, firmware generates a packet like:
> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
> (just masked 2 bytes of my MAC)
>
> For mode details you can see discussion in my brcmfmac patch thread:
> https://patchwork.kernel.org/patch/10191451/
>
>
> The problem is that bridge (in setup as above) handles such a packet
> back to the device.
>
> That makes Broadcom's FullMAC firmware believe that a given station
> just connected to another AP in a network (which doesn't even exist).
> As a result firmware immediately disassociates that station. It's
> simply impossible to connect to the router. Every association is
> followed by immediate disassociation.
>
>
> Can you see any solution for this problem? Is that an option to stop
> multicast-to-unicast from touching 802.11f packets? Some other ideas?
> Obviously I can't modify Broadcom's firmware and drop that obsoleted
> standard.

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Arend van Spriel]

On 2/27/2018 11:14 AM, Rafał Miłecki wrote:
> Sending with a fixed linux-wireless ML address. Please kindly send your
> replies using linux-wireless@
>
> On 02/27/2018 11:08 AM, Rafał Miłecki wrote:
>> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>> FullMAC WiFi chipset.
>>
>>
>> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
>> 1) IFLA_BRPORT_MCAST_TO_UCAST
>> 2) Clients isolation in hostapd
>> 3) Hairpin mode enabled
>>
>> For more details please see Linus's patch description:
>> https://patchwork.kernel.org/patch/9530669/
>> and maybe hairpin mode patch:
>> https://lwn.net/Articles/347344/
>>
>> Short version: in that setup packets received from a bridged wireless
>> interface can be handled back to it for transmission.
>>
>>
>> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
>> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
>> standard that was replaced by 802.11r.
>>
>> Whenever a new station associates, firmware generates a packet like:
>> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
>> (just masked 2 bytes of my MAC)
>>
>> For mode details you can see discussion in my brcmfmac patch thread:
>> https://patchwork.kernel.org/patch/10191451/
>>
>>
>> The problem is that bridge (in setup as above) handles such a packet
>> back to the device.

 From reading the referenced links I understand the hairpin mode is 
causing the packet to be sent back to the device, and the hairpin mode 
is required for MCAST_TO_UCAST, right?

>> That makes Broadcom's FullMAC firmware believe that a given station
>> just connected to another AP in a network (which doesn't even exist).
>> As a result firmware immediately disassociates that station. It's
>> simply impossible to connect to the router. Every association is
>> followed by immediate disassociation.
>>
>>
>> Can you see any solution for this problem? Is that an option to stop
>> multicast-to-unicast from touching 802.11f packets? Some other ideas?
>> Obviously I can't modify Broadcom's firmware and drop that obsoleted
>> standard.

As far as I can tell you are correct that the 802.11f amendment was 
never adopted into the 802.11 standard. I will ask internally if we 
still have a reason for carrying it in our firmware.

Regards,
Arend

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 28 February 2018 at 12:31, Arend van Spriel
<arend.vanspriel@broadcom.com> wrote:
> On 2/27/2018 11:14 AM, Rafa=C5=82 Mi=C5=82ecki wrote:
>>
>> Sending with a fixed linux-wireless ML address. Please kindly send your
>> replies using linux-wireless@
>>
>> On 02/27/2018 11:08 AM, Rafa=C5=82 Mi=C5=82ecki wrote:
>>>
>>> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>>> FullMAC WiFi chipset.
>>>
>>>
>>> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
>>> 1) IFLA_BRPORT_MCAST_TO_UCAST
>>> 2) Clients isolation in hostapd
>>> 3) Hairpin mode enabled
>>>
>>> For more details please see Linus's patch description:
>>> https://patchwork.kernel.org/patch/9530669/
>>> and maybe hairpin mode patch:
>>> https://lwn.net/Articles/347344/
>>>
>>> Short version: in that setup packets received from a bridged wireless
>>> interface can be handled back to it for transmission.
>>>
>>>
>>> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
>>> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
>>> standard that was replaced by 802.11r.
>>>
>>> Whenever a new station associates, firmware generates a packet like:
>>> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
>>> (just masked 2 bytes of my MAC)
>>>
>>> For mode details you can see discussion in my brcmfmac patch thread:
>>> https://patchwork.kernel.org/patch/10191451/
>>>
>>>
>>> The problem is that bridge (in setup as above) handles such a packet
>>> back to the device.
>
>
> From reading the referenced links I understand the hairpin mode is causin=
g
> the packet to be sent back to the device, and the hairpin mode is require=
d
> for MCAST_TO_UCAST, right?
>
>>> That makes Broadcom's FullMAC firmware believe that a given station
>>> just connected to another AP in a network (which doesn't even exist).
>>> As a result firmware immediately disassociates that station. It's
>>> simply impossible to connect to the router. Every association is
>>> followed by immediate disassociation.
>>>
>>>
>>> Can you see any solution for this problem? Is that an option to stop
>>> multicast-to-unicast from touching 802.11f packets? Some other ideas?
>>> Obviously I can't modify Broadcom's firmware and drop that obsoleted
>>> standard.
>
>
> As far as I can tell you are correct that the 802.11f amendment was never
> adopted into the 802.11 standard. I will ask internally if we still have =
a
> reason for carrying it in our firmware.

Thanks! Having at least a way to disable it would be nice.

That said I think we still should look for a solution for existing
firmwares. I guess it may takes months to years to never to release
new firmwares for all supported chipsets.

--=20
Rafa=C5=82

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 27 February 2018 at 18:05, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Tue, 27 Feb 2018 11:08:20 +0100
> Rafa=C5=82 Mi=C5=82ecki <zajec5@gmail.com> wrote:
>
>> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>> FullMAC WiFi chipset.
>>
>>
>> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
>> 1) IFLA_BRPORT_MCAST_TO_UCAST
>> 2) Clients isolation in hostapd
>> 3) Hairpin mode enabled
>>
>> For more details please see Linus's patch description:
>> https://patchwork.kernel.org/patch/9530669/
>> and maybe hairpin mode patch:
>> https://lwn.net/Articles/347344/
>>
>> Short version: in that setup packets received from a bridged wireless
>> interface can be handled back to it for transmission.
>>
>>
>> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
>> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
>> standard that was replaced by 802.11r.
>>
>> Whenever a new station associates, firmware generates a packet like:
>> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
>> (just masked 2 bytes of my MAC)
>>
>> For mode details you can see discussion in my brcmfmac patch thread:
>> https://patchwork.kernel.org/patch/10191451/
>>
>>
>> The problem is that bridge (in setup as above) handles such a packet
>> back to the device.
>>
>> That makes Broadcom's FullMAC firmware believe that a given station
>> just connected to another AP in a network (which doesn't even exist).
>> As a result firmware immediately disassociates that station. It's
>> simply impossible to connect to the router. Every association is
>> followed by immediate disassociation.
>>
>>
>> Can you see any solution for this problem? Is that an option to stop
>> multicast-to-unicast from touching 802.11f packets? Some other ideas?
>> Obviously I can't modify Broadcom's firmware and drop that obsoleted
>> standard.
>>
>
> ebtables is your friend in dealing with weird and broken devices.

It may be weird, not sure if actually broken. Anyway I'd like to have
some generic solution instead of telling every user to use ebtables to
workaround the problem.

--=20
Rafa=C5=82

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Linus Lüssing]

On Mon, Mar 12, 2018 at 10:46:45AM +0100, Rafał Miłecki wrote:
> On 27 February 2018 at 18:05, Stephen Hemminger
[...]
> > ebtables is your friend in dealing with weird and broken devices.
> 
> It may be weird, not sure if actually broken. Anyway I'd like to have
> some generic solution instead of telling every user to use ebtables to
> workaround the problem.

I agree that a "broken by default" in OpenWRT/LEDE for a variety
of Broadcom devices is not really acceptable.

Technically we could teach netifd in OpenWRT/LEDE to configure
ebtables accordingly, at least for a list of affected devices,
so that users would not have to. However, as ebtables is not
managed by the fw3 in OpenWRT/LEDE, that would probably interfer
with user provided ebtables rules and scripts...


> That said I think we still should look for a solution for existing
> firmwares. I guess it may takes months to years to never to release
> new firmwares for all supported chipsets.

Hm, we could change the default in OpenWRT/LEDE for
multicast-to-unicast (or more precisely bridge hairpinning) to
disabled again for now.

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Linus Lüssing]

On Tue, Feb 27, 2018 at 11:08:20AM +0100, Rafał Miłecki wrote:
> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
> FullMAC WiFi chipset.

Hi Rafał,

Thanks for reporting this issue!

> Can you see any solution for this problem? Is that an option to stop
> multicast-to-unicast from touching 802.11f packets? Some other ideas?
> Obviously I can't modify Broadcom's firmware and drop that obsoleted
> standard.

Just to avoid some potential confusion: This is more an issue of
hairpinning than it is an issue of multicast-to-unicast per se,
right?

That is, if you set this to 0 manually:
/sys/class/net/<ap-iface>/brport/multicast_to_unicast
Then the issue still occurs, right?

Regards, Linus

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Linus Lüssing]

On Mon, Mar 12, 2018 at 12:08:56PM +0100, Linus Lüssing wrote:
> On Tue, Feb 27, 2018 at 11:08:20AM +0100, Rafał Miłecki wrote:
> > I've problem when using OpenWrt/LEDE on a home router with Broadcom's
> > FullMAC WiFi chipset.
> 
> Hi Rafał,
> 
> Thanks for reporting this issue!
> 
> > Can you see any solution for this problem? Is that an option to stop
> > multicast-to-unicast from touching 802.11f packets? Some other ideas?
> > Obviously I can't modify Broadcom's firmware and drop that obsoleted
> > standard.
> 
> Just to avoid some potential confusion: This is more an issue of
> hairpinning than it is an issue of multicast-to-unicast per se,
> right?
> 
> That is, if you set this to 0 manually:
> /sys/class/net/<ap-iface>/brport/multicast_to_unicast
> Then the issue still occurs, right?

Btw., if in OpenWRT/LEDE you set 'option multicast_to_unicast 0'
in /etc/config/network for the bridge (and not bridge port)
then netifd should refrain from setting the bridge hairpinning and
AP isolation on wireless devices, too, if I remember correctly.

Can you confirm that the issue disappears for you then?

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 12 March 2018 at 12:48, Linus L=C3=BCssing <linus.luessing@c0d3.blue> wr=
ote:
> On Mon, Mar 12, 2018 at 12:08:56PM +0100, Linus L=C3=BCssing wrote:
>> On Tue, Feb 27, 2018 at 11:08:20AM +0100, Rafa=C5=82 Mi=C5=82ecki wrote:
>> > I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>> > FullMAC WiFi chipset.
>>
>> Hi Rafa=C5=82,
>>
>> Thanks for reporting this issue!
>>
>> > Can you see any solution for this problem? Is that an option to stop
>> > multicast-to-unicast from touching 802.11f packets? Some other ideas?
>> > Obviously I can't modify Broadcom's firmware and drop that obsoleted
>> > standard.
>>
>> Just to avoid some potential confusion: This is more an issue of
>> hairpinning than it is an issue of multicast-to-unicast per se,
>> right?
>>
>> That is, if you set this to 0 manually:
>> /sys/class/net/<ap-iface>/brport/multicast_to_unicast
>> Then the issue still occurs, right?
>
> Btw., if in OpenWRT/LEDE you set 'option multicast_to_unicast 0'
> in /etc/config/network for the bridge (and not bridge port)
> then netifd should refrain from setting the bridge hairpinning and
> AP isolation on wireless devices, too, if I remember correctly.
>
> Can you confirm that the issue disappears for you then?

Yes, absolutely. This reverts OpenWrt/LEDE to the old setup (no
mcast-to-ucast + hairpin) and it works. I was hoping we can make
mcast-to-ucast + hairpin work with Broadcom's 802.11f however instead
of moving OpenWrt/LEDE back to the old setup.

--=20
Rafa=C5=82

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 12 March 2018 at 12:08, Linus L=C3=BCssing <linus.luessing@c0d3.blue> wr=
ote:
> On Tue, Feb 27, 2018 at 11:08:20AM +0100, Rafa=C5=82 Mi=C5=82ecki wrote:
>> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>> FullMAC WiFi chipset.
>
> Hi Rafa=C5=82,
>
> Thanks for reporting this issue!
>
>> Can you see any solution for this problem? Is that an option to stop
>> multicast-to-unicast from touching 802.11f packets? Some other ideas?
>> Obviously I can't modify Broadcom's firmware and drop that obsoleted
>> standard.
>
> Just to avoid some potential confusion: This is more an issue of
> hairpinning than it is an issue of multicast-to-unicast per se,
> right?
>
> That is, if you set this to 0 manually:
> /sys/class/net/<ap-iface>/brport/multicast_to_unicast
> Then the issue still occurs, right?

I can't really tell, I didn't go into details on bridge +
mcast-to-unicast + hairpin.

By default OpenWrt/LEDE sets
/sys/class/net/<ap-iface>/brport/multicast_to_unicast
to 1. Changing it to 0 (with a simple echo) doesn't /fix/ the problem.

--=20
Rafa=C5=82

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 02/27/2018 11:08 AM, Rafał Miłecki wrote:
> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
> FullMAC WiFi chipset.
>
>
> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
> 1) IFLA_BRPORT_MCAST_TO_UCAST
> 2) Clients isolation in hostapd
> 3) Hairpin mode enabled
>
> For more details please see Linus's patch description:
> https://patchwork.kernel.org/patch/9530669/
> and maybe hairpin mode patch:
> https://lwn.net/Articles/347344/
>
> Short version: in that setup packets received from a bridged wireless
> interface can be handled back to it for transmission.
>
>
> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
> standard that was replaced by 802.11r.
>
> Whenever a new station associates, firmware generates a packet like:
> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
> (just masked 2 bytes of my MAC)
>
> For mode details you can see discussion in my brcmfmac patch thread:
> https://patchwork.kernel.org/patch/10191451/
>
>
> The problem is that bridge (in setup as above) handles such a packet
> back to the device.
>
> That makes Broadcom's FullMAC firmware believe that a given station
> just connected to another AP in a network (which doesn't even exist).
> As a result firmware immediately disassociates that station. It's
> simply impossible to connect to the router. Every association is
> followed by immediate disassociation.
>
>
> Can you see any solution for this problem? Is that an option to stop
> multicast-to-unicast from touching 802.11f packets? Some other ideas?
> Obviously I can't modify Broadcom's firmware and drop that obsoleted
> standard.

I kept thinking about this for a bit more. We probably have to start
with deciding what to blame for this problem. I see two options I'll
describe below.

Please share your opinions on this.


1) Blame brcmfmac fw for implementing 802.11f

In that case we should add workaround to brcmfmac driver to drop/ignore
802.11f packets. A slightly improved version of my
[PATCH] brcmfmac: detect & reject faked packet generated by a firmware
https://patchwork.kernel.org/patch/10191451/
should work.


2) Blame bridge + mcast-to-ucast + hairpin for 802.11f incompatibility

If we agree that 802.11f support in FullMAC firmware is acceptable, then
we have to make sure Linux's bridge doesn't break it by passing 802.11f
(broadcast) frames back to the source interface. That would require a
check like in below diff + proper code for handling such packets. I'm
afraid I'm not familiar with bridge code enough to complete that.

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index edae702..9e5d6ea 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -126,6 +126,27 @@ static void br_do_proxy_arp(struct sk_buff *skb, struct net_bridge *br,
  	}
  }

+static bool br_skb_is_iapp_add_packet(struct sk_buff *skb)
+{
+	const u8 iapp_add_packet[6] __aligned(2) = {
+		0x00, 0x01, 0xaf, 0x81, 0x01, 0x00,
+	};
+#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+	const u16 *a = (const u16 *)skb->data;
+	const u16 *b = (const u16 *)iapp_add_packet;
+#endif
+
+	if (skb->len != 6)
+		return false;
+
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+	return !(((*(const u32 *)skb->data) ^ (*(const u32 *)iapp_add_packet)) |
+	         ((*(const u16 *)(skb->data + 4)) ^ (*(const u16 *)(iapp_add_packet + 4))));
+#else
+	return !((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2]));
+#endif
+}
+
  /* note: already called with rcu_read_lock */
  int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
  {
@@ -155,6 +176,8 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
  	if (is_multicast_ether_addr(dest)) {
  		/* by definition the broadcast is also a multicast address */
  		if (is_broadcast_ether_addr(dest)) {
+			if (br_skb_is_iapp_add_packet(skb))
+				pr_warn("This packet should not be passed back to the source interface!\n");
  			pkt_type = BR_PKT_BROADCAST;
  			local_rcv = true;
  		} else {

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Rafał Miłecki]

On 03/13/2018 12:01 AM, Stephen Hemminger wrote:
> On Mon, 12 Mar 2018 23:42:48 +0100
> Rafał Miłecki <zajec5@gmail.com> wrote:
>
>> 2) Blame bridge + mcast-to-ucast + hairpin for 802.11f incompatibility
>>
>> If we agree that 802.11f support in FullMAC firmware is acceptable, then
>> we have to make sure Linux's bridge doesn't break it by passing 802.11f
>> (broadcast) frames back to the source interface. That would require a
>> check like in below diff + proper code for handling such packets. I'm
>> afraid I'm not familiar with bridge code enough to complete that.
>>
>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>> index edae702..9e5d6ea 100644
>> --- a/net/bridge/br_input.c
>> +++ b/net/bridge/br_input.c
>> @@ -126,6 +126,27 @@ static void br_do_proxy_arp(struct sk_buff *skb, struct net_bridge *br,
>>   	}
>>   }
>>
>> +static bool br_skb_is_iapp_add_packet(struct sk_buff *skb)
>> +{
>> +	const u8 iapp_add_packet[6] __aligned(2) = {
>> +		0x00, 0x01, 0xaf, 0x81, 0x01, 0x00,
>> +	};
>> +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
>> +	const u16 *a = (const u16 *)skb->data;
>> +	const u16 *b = (const u16 *)iapp_add_packet;
>> +#endif
>> +
>> +	if (skb->len != 6)
>> +		return false;
>> +
>> +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
>> +	return !(((*(const u32 *)skb->data) ^ (*(const u32 *)iapp_add_packet)) |
>> +	         ((*(const u16 *)(skb->data + 4)) ^ (*(const u16 *)(iapp_add_packet + 4))));
>> +#else
>> +	return !((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2]));
>> +#endif
>> +}
>> +
>>   /* note: already called with rcu_read_lock */
>>   int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
>>   {
>> @@ -155,6 +176,8 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>>   	if (is_multicast_ether_addr(dest)) {
>>   		/* by definition the broadcast is also a multicast address */
>>   		if (is_broadcast_ether_addr(dest)) {
>> +			if (br_skb_is_iapp_add_packet(skb))
>> +				pr_warn("This packet should not be passed back to the source interface!\n");
>>   			pkt_type = BR_PKT_BROADCAST;
>>   			local_rcv = true;
>>   		} else {
>
>
> Don't like bridge doing special case code for magic received values directly in input path.
> Really needs to be generic which is why I suggested ebtables.

We need in-bridge solution only if we decide to support FullMAC
firmwares with 802.11f implementation.

In that case is this possible to use ebtables as a workaround at all?
Can I really use ebtables to set switch to don't pass 802.11f ADD frames
back to the original interface?

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Felix Fietkau]

[resent with fixed typo in linux-wireless address]

On 2018-02-27 11:08, Rafał Miłecki wrote:
> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
> FullMAC WiFi chipset.
> 
> 
> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
> 1) IFLA_BRPORT_MCAST_TO_UCAST
> 2) Clients isolation in hostapd
> 3) Hairpin mode enabled
> 
> For more details please see Linus's patch description:
> https://patchwork.kernel.org/patch/9530669/
> and maybe hairpin mode patch:
> https://lwn.net/Articles/347344/
> 
> Short version: in that setup packets received from a bridged wireless
> interface can be handled back to it for transmission.
> 
> 
> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
> standard that was replaced by 802.11r.
> 
> Whenever a new station associates, firmware generates a packet like:
> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
> (just masked 2 bytes of my MAC)
> 
> For mode details you can see discussion in my brcmfmac patch thread:
> https://patchwork.kernel.org/patch/10191451/
> 
> 
> The problem is that bridge (in setup as above) handles such a packet
> back to the device.
> 
> That makes Broadcom's FullMAC firmware believe that a given station
> just connected to another AP in a network (which doesn't even exist).
> As a result firmware immediately disassociates that station. It's
> simply impossible to connect to the router. Every association is
> followed by immediate disassociation.
> 
> 
> Can you see any solution for this problem? Is that an option to stop
> multicast-to-unicast from touching 802.11f packets? Some other ideas?
> Obviously I can't modify Broadcom's firmware and drop that obsoleted
> standard.
Let's look at it from a different angle: Since these packets are
forwarded as normal packets by the bridge, and the Broadcom firmware
reacts to them in this nasty way, that's basically local DoS security
issue. In my opinion that matters a lot more than having support for an
obsolete feature that almost nobody will ever want to use.

I think the right approach to deal with this issue is to drop these
garbage packets in both the receive and transmit path of brcmfmac.

- Felix

Re: Problem with bridge (mcast-to-ucast + hairpin) and Broadcom's 802.11f in their FullMAC fw

[Arend van Spriel]

On 3/13/2018 8:20 AM, Felix Fietkau wrote:
> [resent with fixed typo in linux-wireless address]
>
> On 2018-02-27 11:08, Rafał Miłecki wrote:
>> I've problem when using OpenWrt/LEDE on a home router with Broadcom's
>> FullMAC WiFi chipset.
>>
>>
>> First of all OpenWrt/LEDE uses bridge interface for LAN network with:
>> 1) IFLA_BRPORT_MCAST_TO_UCAST
>> 2) Clients isolation in hostapd
>> 3) Hairpin mode enabled
>>
>> For more details please see Linus's patch description:
>> https://patchwork.kernel.org/patch/9530669/
>> and maybe hairpin mode patch:
>> https://lwn.net/Articles/347344/
>>
>> Short version: in that setup packets received from a bridged wireless
>> interface can be handled back to it for transmission.
>>
>>
>> Now, Broadcom's firmware for their FullMAC chipsets in AP mode
>> supports an obsoleted 802.11f AKA IAPP standard. It's a roaming
>> standard that was replaced by 802.11r.
>>
>> Whenever a new station associates, firmware generates a packet like:
>> ff ff ff ff  ff ff ec 10  7b 5f ?? ??  00 06 00 01  af 81 01 00
>> (just masked 2 bytes of my MAC)
>>
>> For mode details you can see discussion in my brcmfmac patch thread:
>> https://patchwork.kernel.org/patch/10191451/
>>
>>
>> The problem is that bridge (in setup as above) handles such a packet
>> back to the device.
>>
>> That makes Broadcom's FullMAC firmware believe that a given station
>> just connected to another AP in a network (which doesn't even exist).
>> As a result firmware immediately disassociates that station. It's
>> simply impossible to connect to the router. Every association is
>> followed by immediate disassociation.
>>
>>
>> Can you see any solution for this problem? Is that an option to stop
>> multicast-to-unicast from touching 802.11f packets? Some other ideas?
>> Obviously I can't modify Broadcom's firmware and drop that obsoleted
>> standard.
> Let's look at it from a different angle: Since these packets are
> forwarded as normal packets by the bridge, and the Broadcom firmware
> reacts to them in this nasty way, that's basically local DoS security
> issue. In my opinion that matters a lot more than having support for an
> obsolete feature that almost nobody will ever want to use.
>
> I think the right approach to deal with this issue is to drop these
> garbage packets in both the receive and transmit path of brcmfmac.

My approach was to get rid of it in firmware as this never made it into 
the 802.11 spec. So I asked internally whether it was still used. Turns 
out that we still rely on it for some customers. I am fine with dropping 
these "garbage" packets, but given that there is still use for it I 
would like to see that under a Kconfig flag. Dropping it may be the default.

Regards,
Arend