linux-kernel - Re: [PATCH v4 1/2] netfilter: Terminate rule eval if protocol=IPv6 and ipv6 module is disabled

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Message-ID: <20190903170550.GA13660@breakpoint.cc>
Date:   Tue, 3 Sep 2019 19:05:50 +0200
From:   Florian Westphal <fw@...len.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Leonardo Bras <leonardo@...ux.ibm.com>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, FlorianWestphal <fw@...len.de>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v4 1/2] netfilter: Terminate rule eval if protocol=IPv6
 and ipv6 module is disabled

Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Tue, Sep 03, 2019 at 01:46:50PM -0300, Leonardo Bras wrote:
> > On Fri, 2019-08-30 at 22:58 +0200, Florian Westphal wrote:
> > > Leonardo Bras <leonardo@...ux.ibm.com> wrote:
> > > > If IPv6 is disabled on boot (ipv6.disable=1), but nft_fib_inet ends up
> > > > dealing with a IPv6 packet, it causes a kernel panic in
> > > > fib6_node_lookup_1(), crashing in bad_page_fault.
> > > > 
> > > > The panic is caused by trying to deference a very low address (0x38
> > > > in ppc64le), due to ipv6.fib6_main_tbl = NULL.
> > > > BUG: Kernel NULL pointer dereference at 0x00000038
> > > > 
> > > > The kernel panic was reproduced in a host that disabled IPv6 on boot and
> > > > have to process guest packets (coming from a bridge) using it's ip6tables.
> > > > 
> > > > Terminate rule evaluation when packet protocol is IPv6 but the ipv6 module
> > > > is not loaded.
> > > > 
> > > > Signed-off-by: Leonardo Bras <leonardo@...ux.ibm.com>
> > > 
> > > Acked-by: Florian Westphal <fw@...len.de>
> > > 
> > 
> > Hello Pablo,
> > 
> > Any trouble with this patch? 
> > I could see the other* one got applied, but not this one.
> > *(The other did not get acked, so i released it alone as v5)
> > 
> > Is there any fix I need to do in this one?
> 
> Hm, I see, so this one:
> 
> https://patchwork.ozlabs.org/patch/1156100/
> 
> is not enough?

No, its not.

> I was expecting we could find a way to handle this from br_netfilter
> alone itself.

We can't because we support ipv6 fib lookups from the netdev family
as well.

Alternative is to auto-accept ipv6 packets from the nf_tables eval loop,
but I think its worse.