Re: [PATCH v4 2/2] net: br_netfiler_hooks: Drops IPv6 packets if IPv6 module is not loaded

Florian Westphal
2019-08-30T20:55:52Z

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.
>
> IPv6 packets need to be dropped if the IPv6 module is not loaded.
>
> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
> net/bridge/br_netfilter_hooks.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> 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 = 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;

No, thats too aggressive and turns the bridge into an ipv6 blackhole.

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.

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.

I would go with option two.