linux-kernel - Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature

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Message-ID: <Yo+LAj1vnjq0p36q@shredder>
Date:   Thu, 26 May 2022 17:13:22 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Hans Schultz <schultz.hans@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Hans Schultz <schultz.hans+netdev@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Shuah Khan <shuah@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Ido Schimmel <idosch@...dia.com>, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent
 locked port feature

On Tue, May 24, 2022 at 05:21:41PM +0200, Hans Schultz wrote:
> Add an intermediate state for clients behind a locked port to allow for
> possible opening of the port for said clients. This feature corresponds
> to the Mac-Auth and MAC Authentication Bypass (MAB) named features. The
> latter defined by Cisco.
> Locked FDB entries will be limited in number, so as to prevent DOS
> attacks by spamming the port with random entries. The limit will be
> a per port limit as it is a port based feature and that the port flushes
> all FDB entries on link down.

Why locked FDB entries need a special treatment compared to regular
entries? A port that has learning enabled can be spammed with random
source MACs just as well.

The authorization daemon that is monitoring FDB notifications can have a
policy to shut down a port if the rate / number of locked entries is
above a given threshold.

I don't think this kind of policy belongs in the kernel. If it resides
in user space, then the threshold can be adjusted. Currently it's hard
coded to 64 and I don't see how user space can change or monitor it.