Linux Ethernet Bridging - Nov 2022 - [Bridge] [PATCH net-next 1/2] bridge: Add MAC Authentication Bypass (MAB) support

On Tue, Nov 01, 2022 at 09:39:21PM +0200, Ido Schimmel
wrote:
> From: "Hans J. Schultz" <netdev at kapio-technology.com>
> 
> Hosts that support 802.1X authentication are able to authenticate
> themselves by exchanging EAPOL frames with an authenticator (Ethernet
> bridge, in this case) and an authentication server. Access to the
> network is only granted by the authenticator to successfully
> authenticated hosts.
> 
> The above is implemented in the bridge using the "locked" bridge
port
> option. When enabled, link-local frames (e.g., EAPOL) can be locally
> received by the bridge, but all other frames are dropped unless the host
> is authenticated. That is, unless the user space control plane installed
> an FDB entry according to which the source address of the frame is
> located behind the locked ingress port. The entry can be dynamic, in
> which case learning needs to be enabled so that the entry will be
> refreshed by incoming traffic.
> 
> There are deployments in which not all the devices connected to the
> authenticator (the bridge) support 802.1X. Such devices can include
> printers and cameras. One option to support such deployments is to
> unlock the bridge ports connecting these devices, but a slightly more
> secure option is to use MAB. When MAB is enabled, the MAC address of the
> connected device is used as the user name and password for the
> authentication.
> 
> For MAB to work, the user space control plane needs to be notified about
> MAC addresses that are trying to gain access so that they will be
> compared against an allow list. This can be implemented via the regular
> learning process with the sole difference that learned FDB entries are
> installed with a new "locked" flag indicating that the entry
cannot be
> used to authenticate the device. The flag cannot be set by user space,
> but user space can clear the flag by replacing the entry, thereby
> authenticating the device.
> 
> Locked FDB entries implement the following semantics with regards to
> roaming, aging and forwarding:
> 
> 1. Roaming: Locked FDB entries can roam to unlocked (authorized) ports,
>    in which case the "locked" flag is cleared. FDB entries cannot
roam
>    to locked ports regardless of MAB being enabled or not. Therefore,
>    locked FDB entries are only created if an FDB entry with the given {MAC,
>    VID} does not already exist. This behavior prevents unauthenticated
>    devices from disrupting traffic destined to already authenticated
>    devices.
> 
> 2. Aging: Locked FDB entries age and refresh by incoming traffic like
>    regular entries.
> 
> 3. Forwarding: Locked FDB entries forward traffic like regular entries.
>    If user space detects an unauthorized MAC behind a locked port and
>    wishes to prevent traffic with this MAC DA from reaching the host, it
>    can do so using tc or a different mechanism.
In other words, a user space MAB daemon has a lot of extra work to do.
I'm willing to bet it's going to cut 90% of those corners ;) anyway...
> 
> Enable the above behavior using a new bridge port option called
"mab".
> It can only be enabled on a bridge port that is both locked and has
> learning enabled. Locked FDB entries are flushed from the port once MAB
> is disabled. A new option is added because there are pure 802.1X
> deployments that are not interested in notifications about locked FDB
> entries.
> 
> Signed-off-by: Hans J. Schultz <netdev at kapio-technology.com>
> Signed-off-by: Ido Schimmel <idosch at nvidia.com>
> ---
Reviewed-by: Vladimir Oltean <vladimir.oltean at nxp.com>

On 2022-11-04 00:18, Vladimir Oltean wrote:
> On Tue, Nov 01, 2022 at 09:39:21PM +0200, Ido Schimmel wrote:
>> From: "Hans J. Schultz" <netdev at
kapio-technology.com>
>> 
>> Hosts that support 802.1X authentication are able to authenticate
>> themselves by exchanging EAPOL frames with an authenticator (Ethernet
>> bridge, in this case) and an authentication server. Access to the
>> network is only granted by the authenticator to successfully
>> authenticated hosts.
>> 
>> The above is implemented in the bridge using the "locked"
bridge port
>> option. When enabled, link-local frames (e.g., EAPOL) can be locally
>> received by the bridge, but all other frames are dropped unless the 
>> host
>> is authenticated. That is, unless the user space control plane 
>> installed
>> an FDB entry according to which the source address of the frame is
>> located behind the locked ingress port. The entry can be dynamic, in
>> which case learning needs to be enabled so that the entry will be
>> refreshed by incoming traffic.
>> 
>> There are deployments in which not all the devices connected to the
>> authenticator (the bridge) support 802.1X. Such devices can include
>> printers and cameras. One option to support such deployments is to
>> unlock the bridge ports connecting these devices, but a slightly more
>> secure option is to use MAB. When MAB is enabled, the MAC address of 
>> the
>> connected device is used as the user name and password for the
>> authentication.
>> 
>> For MAB to work, the user space control plane needs to be notified 
>> about
>> MAC addresses that are trying to gain access so that they will be
>> compared against an allow list. This can be implemented via the 
>> regular
>> learning process with the sole difference that learned FDB entries are
>> installed with a new "locked" flag indicating that the entry
cannot be
>> used to authenticate the device. The flag cannot be set by user space,
>> but user space can clear the flag by replacing the entry, thereby
>> authenticating the device.
>> 
>> Locked FDB entries implement the following semantics with regards to
>> roaming, aging and forwarding:
>> 
>> 1. Roaming: Locked FDB entries can roam to unlocked (authorized) 
>> ports,
>>    in which case the "locked" flag is cleared. FDB entries
cannot roam
>>    to locked ports regardless of MAB being enabled or not. Therefore,
>>    locked FDB entries are only created if an FDB entry with the given 
>> {MAC,
>>    VID} does not already exist. This behavior prevents unauthenticated
>>    devices from disrupting traffic destined to already authenticated
>>    devices.
>> 
>> 2. Aging: Locked FDB entries age and refresh by incoming traffic like
>>    regular entries.
>> 
>> 3. Forwarding: Locked FDB entries forward traffic like regular 
>> entries.
>>    If user space detects an unauthorized MAC behind a locked port and
>>    wishes to prevent traffic with this MAC DA from reaching the host, 
>> it
>>    can do so using tc or a different mechanism.
> 
> In other words, a user space MAB daemon has a lot of extra work to do.
> I'm willing to bet it's going to cut 90% of those corners ;)
anyway...
> 
I would like to know your (Vladimir) take on the approach of the
implementation for the mv88e6xxx that I have made and which will also be
the basis for how the WesterMo hostapd fork will be afaik...

Is it in general a good idea to use TC filters for specific MACs instead
of having the driver installing blocking entries, which I know the 
Marvell
XCat switchcore will also have (switchcore installed blockig entries)?

>> 
>> Enable the above behavior using a new bridge port option called
"mab".
>> It can only be enabled on a bridge port that is both locked and has
>> learning enabled. Locked FDB entries are flushed from the port once 
>> MAB
>> is disabled. A new option is added because there are pure 802.1X
>> deployments that are not interested in notifications about locked FDB
>> entries.
>> 
>> Signed-off-by: Hans J. Schultz <netdev at kapio-technology.com>
>> Signed-off-by: Ido Schimmel <idosch at nvidia.com>
>> ---
> 
> Reviewed-by: Vladimir Oltean <vladimir.oltean at nxp.com>