Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <2ba876f9ad6597e640df68f09659dce3c4b5ce03.camel@linux.ibm.com>
Subject: Re: [PATCH v4 2/2] net: br_netfiler_hooks: Drops IPv6 packets if
 IPv6 module is not loaded
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     Florian Westphal <fw@strlen.de>
Cc:     netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Roopa Prabhu <roopa@cumulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@cumulusnetworks.com>,
        "David S. Miller" <davem@davemloft.net>
Date:   Sat, 31 Aug 2019 01:42:29 -0300
In-Reply-To: <20190830205541.GR20113@breakpoint.cc>
References: <20190830181354.26279-1-leonardo@linux.ibm.com>
         <20190830181354.26279-3-leonardo@linux.ibm.com>
         <20190830205541.GR20113@breakpoint.cc>
Content-Type: multipart/signed; micalg="pgp-sha256";
        protocol="application/pgp-signature"; boundary="=-NmceabA7waNjtZ157fkz"
User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) 
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--=-NmceabA7waNjtZ157fkz
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Fri, 2019-08-30 at 22:55 +0200, Florian Westphal wrote:
> Leonardo Bras <leonardo@linux.ibm.com> wrote:
> > A kernel panic can happen if a host has disabled IPv6 on boot and have =
to
> > process guest packets (coming from a bridge) using it's ip6tables.
> >=20
> > IPv6 packets need to be dropped if the IPv6 module is not loaded.
> >=20
> > Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> > ---
> >  net/bridge/br_netfilter_hooks.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >=20
> > diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_=
hooks.c
> > index d3f9592f4ff8..5e8693730df1 100644
> > --- a/net/bridge/br_netfilter_hooks.c
> > +++ b/net/bridge/br_netfilter_hooks.c
> > @@ -493,6 +493,8 @@ static unsigned int br_nf_pre_routing(void *priv,
> >  	brnet =3D net_generic(state->net, brnf_net_id);
> >  	if (IS_IPV6(skb) || is_vlan_ipv6(skb, state->net) ||
> >  	    is_pppoe_ipv6(skb, state->net)) {
> > +		if (!ipv6_mod_enabled())
> > +			return NF_DROP;
> >  		if (!brnet->call_ip6tables &&
> >  		    !br_opt_get(br, BROPT_NF_CALL_IP6TABLES))
> >  			return NF_ACCEPT;
>=20
> No, thats too aggressive and turns the bridge into an ipv6 blackhole.
>=20
> There are two solutions:
> 1. The above patch, but use NF_ACCEPT instead
> 2. keep the DROP, but move it below the call_ip6tables test,
>    so that users can tweak call-ip6tables to accept packets.

Q: Does 2 mean that it will only be dropped if bridge intents to use
host's ip6tables? Else, it will be accepted by previous if?

> Perhaps it would be good to also add a pr_warn_once() that
> tells that ipv6 was disabled on command line and
> call-ip6tables isn't supported in this configuration.
>=20
Good idea, added.

> I would go with option two.
I think it's better than 1 too.

I sent a v5 with these changes:
https://lkml.org/lkml/2019/8/31/4

Thanks!

Leonardo Bras

--=-NmceabA7waNjtZ157fkz
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: This is a digitally signed message part
Content-Transfer-Encoding: 7bit

-----BEGIN PGP SIGNATURE-----
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=lpBD
-----END PGP SIGNATURE-----

--=-NmceabA7waNjtZ157fkz--