[PATCH v5 1/1] net: br_netfiler_hooks: Drops IPv6 packets if IPv6 module is not loaded

From: Leonardo Bras
Date: Sat Aug 31 2019 - 00:41:19 EST

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, and the
host ip6tables will be used.

Signed-off-by: Leonardo Bras <leonardo@xxxxxxxxxxxxx>
Changes from v4:
- Check if the host ip6tables is going to be used before testing
ipv6 module presence
- Adds a warning about ipv6 module disabled.

net/bridge/br_netfilter_hooks.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index d3f9592f4ff8..af7800103e51 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -496,6 +496,10 @@ static unsigned int br_nf_pre_routing(void *priv,
if (!brnet->call_ip6tables &&
!br_opt_get(br, BROPT_NF_CALL_IP6TABLES))
return NF_ACCEPT;
+ if (!ipv6_mod_enabled()) {
+ pr_warn_once("Module ipv6 is disabled, so call_ip6tables is not supported.");
+ return NF_DROP;
+ }

return br_nf_pre_routing_ipv6(priv, skb, state);