netdev - Re: [PATCH 2/7] mark root hnode explicitly

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Date:   Thu, 6 Sep 2018 21:14:05 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH 2/7] mark root hnode explicitly

On Thu, Sep 6, 2018 at 8:50 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Thu, Sep 06, 2018 at 08:23:36PM -0700, Cong Wang wrote:
>
> > Pretty sure there is a 'tp' in u32_set_parms() parameter list.
> >
> > Are you saying it is not what you want? If so, why?
> >
> > More importantly, why this information is again missing in your
> > changelog? This patch is definitely not trivial, it deserves a detailed
> > changelog.
> >
> >
> > > our own root, sure.  But there's nothing to stop doing the same via another
> > > tcf_proto...
> >
> > To my best knowledge, the place where you set ->is_root=true
> > is precisely same with where we set tp->root=root_ht, and it doesn't
> > change after set. What am I missing here?
>
> The fact that there can be two (or more) different tcf_proto instances sharing
> ->data, but not ->root.  And since ->data is shared, u32_get() on one tp

They have to share tp->data, that is how we link hashtables together.


> will be able to return you ->root of *ANOTHER* one.  So comparison with
> tp->root doesn't protect you.  Try this on mainline:

Hmm, it is not u32_get(), it is u32_lookup_ht() which could get another
root ht... I see.


>
> tc qdisc add dev eth0 ingress
> tc filter add dev eth0 parent ffff: protocol ip prio 100 handle 1: u32 divisor 1
> tc filter add dev eth0 parent ffff: protocol ip prio 200 handle 2: u32 divisor 1
> tc filter delete dev eth0 parent ffff: protocol ip prio 100 handle 801: u32
>
> and watch the fun as soon as you get an incoming packet on eth0.  That panic
> is fixed by 1/7, but you get "Not allowed to delete root node" for removing
> _your_ root, with "Can not delete in-use filter" for other's root (as in the
> last line of the reproducer).

Sure, please consider:

1. adding such a test case to tools/testing/selftests/tc-testing/
2. adding it in your changelog

This would save a lot of time for both of us. I don't need to ask you for
this if it is in the changelog, you don't have to explain it again.

This is a win-win.