Linux Ethernet Bridging - Aug 2019 - [Bridge] [PATCH v5 1/1] net: br_netfiler_hooks: Drops IPv6 packets if IPv6 module is not loaded

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 at linux.ibm.com>
---
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;
+		}
 
 		nf_bridge_pull_encap_header_rcsum(skb);
 		return br_nf_pre_routing_ipv6(priv, skb, state);
-- 
2.20.1

Leonardo Bras <leonardo at 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, and the
> host ip6tables will be used.
> 
> Signed-off-by: Leonardo Bras <leonardo at linux.ibm.com>
> ---
> 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;
> +		}
pr_warn_once needs a '\n'.  Pablo, can you mangle this locally when
applying?

Patch looks good to me, so:

Acked-by: Florian Westphal <fw at strlen.de>

On Sat, Aug 31, 2019 at 01:40:33AM -0300, Leonardo Bras
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, and the
> host ip6tables will be used.
Applied, thanks.