Linux Ethernet Bridging - Sep 2019 - [Bridge] [PATCH v4 1/2] netfilter: Terminate rule eval if protocol=IPv6 and ipv6 module is disabled

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 at linux.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 at linux.ibm.com>
> > 
> > Acked-by: Florian Westphal <fw at strlen.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?

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

Thanks.

On Tue, 2019-09-03 at 18:49 +0200, Pablo Neira Ayuso
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:
> > 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?
By what I could understand of Florian e-mail, we would need both:
>> So, given I don't want to plaster ipv6_mod_enabled() everywhere, I
>> would suggest this course of action:
>>
>> 1. add a patch to BREAK in nft_fib_netdev.c for !ipv6_mod_enabled()
>> 2. change net/bridge/br_netfilter_hooks.c, br_nf_pre_routing() to
>>    make sure ipv6_mod_enabled() is true before doing the ipv6 stack
>>    "emulation".
Is that ok?
> 
> I was expecting we could find a way to handle this from br_netfilter
> alone itself.
> 
> Thanks.
Thank you!
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Pablo Neira Ayuso <pablo at netfilter.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 at linux.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 at
linux.ibm.com>
> > > 
> > > Acked-by: Florian Westphal <fw at strlen.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.