netdev - Re: [REGRESSION] Userland interface breaks due to hard HFSC

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Date: Tue, 10 Oct 2023 11:02:25 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Pedro Tammela <pctammela@...atatu.com>, markovicbudimir@...il.com, 
	Christian Theune <ct@...ingcircus.io>, stable@...r.kernel.org, netdev@...r.kernel.org, 
	Linux regressions mailing list <regressions@...ts.linux.dev>, davem@...emloft.net, edumazet@...gle.com, 
	pabeni@...hat.com
Subject: Re: [REGRESSION] Userland interface breaks due to hard HFSC_FSC requirement

On Mon, Oct 9, 2023 at 8:28 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 9 Oct 2023 12:31:57 -0300 Pedro Tammela wrote:
> > > Herm, how did we get this far without CCing the author of the patch.
> > > Adding Budimir.
> > >
> > > Pedro, Budimir, any idea what the original bug was? There isn't much
> > > info in the commit message.
> >
> > We had a UAF with a very straight forward way to trigger it.
>
> Any details?

As in you want the sequence of commands that caused the fault posted?
Budimir, lets wait for Jakub's response before you do that. I have
those details as well of course.

> > Setting 'rt' as a parent is incorrect and the man page is explicit about
> > it as it doesn't make sense 'qdisc wise'. Being able to set it has
> > always been wrong unfortunately...
>
> Sure but unfortunately "we don't break backward compat" means
> we can't really argue. It will take us more time to debate this
> than to fix it (assuming we understand the initial problem).
>
> Frankly one can even argue whether "exploitable by root / userns"
> is more important than single user's init scripts breaking.
> The "security" issues for root are dime a dozen.

This is a tough one - as it stands right now we dont see a good way
out. It's either "exploitable by root / userns" or break uapi.
Christian - can you send your "working" scripts, simplified if
possible, and we'll take a look.

cheers,
jamal