netdev - Re: Bug in MACSec - stops passing traffic after approx 5TB

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Message-ID: <CACcUnf8kTNEYW8ZisbEYMr+Pu7rmP7pKS=w+-ynUJ_sT75HZ0w@mail.gmail.com>
Date:   Mon, 15 Oct 2018 11:45:57 -0400
From:   Josh Coombs <jcoombs@...ff.gwi.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org
Subject: Re: Bug in MACSec - stops passing traffic after approx 5TB

And confirmed, starting with a high packet number results in a very
short testbed run, 296 packets and then nothing, just as you surmised.
Sorry for raising the alarm falsely.  Looks like I need to roll my own
build of wpa_supplicant as the ubuntu builds don't include the macsec
driver, haven't tested Gentoo's ebuilds yet to see if they do.

Josh Coombs

On Sun, Oct 14, 2018 at 4:52 PM Josh Coombs <jcoombs@...ff.gwi.net> wrote:
>
> On Sun, Oct 14, 2018 at 4:24 PM Sabrina Dubroca <sd@...asysnail.net> wrote:
> >
> > 2018-10-14, 10:59:31 -0400, Josh Coombs wrote:
> > > I initially mistook this for a traffic control issue, but after
> > > stripping the test beds down to just the MACSec component, I can still
> > > replicate the issue.  After approximately 5TB of transfer / 4 billion
> > > packets over a MACSec link it stops passing traffic.
> >
> > I think you're just hitting packet number exhaustion. After 2^32
> > packets, the packet number would wrap to 0 and start being reused,
> > which breaks the crypto used by macsec. Before this point, you have to
> > add a new SA, and tell the macsec device to switch to it.
>
> I had not considered that, I naively thought as long as I didn't
> specify a replay window, it'd roll the PN over on it's own and life
> would be good.  I'll test that theory tomorrow, should be easy to
> prove out.
>
> > That's why you should be using wpa_supplicant. It will monitor the
> > growth of the packet number, and handle the rekey for you.
>
> Thank you for the heads up, I'll read up on this as well.
>
> Josh C