Re: [PATCHv3 2/2 nf] netfilter: bridge: fix IPv6 packets not being bridged with CONFIG_IPV6=n

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Bernhard,

On Thu, Jul 30, 2015 at 06:07:01AM +0200, Bernhard Thaler wrote:
> 230ac490f7fba introduced a dependency to CONFIG_IPV6 which breaks bridging
> of IPv6 packets on a bridge with CONFIG_IPV6=n. This is due to the default
> value 1 for sysctl entry /proc/sys/net/bridge/bridge-nf-call-ip6tables,
> manually setting it to 0 makes IPv6 packets traverse bridge again.
> 
> Default /proc/sys/net/bridge/bridge-nf-call-ip6tables to 0 if
> CONFIG_IP6_NF_IPTABLES is not enabled as CONFIG_IP6_NF_IPTABLES depends on
> CONFIG_IPV6 as well and is needed for ip6tables to work correctly.
>
> Do not expose sysctl entry /proc/sys/net/bridge/bridge-nf-call-ip6tables
> and sysfs entry /sys/class/net/brXXX/bridge/nf_call_ip6tables if
> CONFIG_IP6_NF_IPTABLES is not enabled.
> 
> Make br_netfilter_ipv6.o dependent on CONFIG_IP6_NF_IPTABLES instead of
> CONFIG_IPV6.

Could you send a patch in first place to
s/CONFIG_IPV6/CONFIG_IP6_NF_IPTABLES ?

More comments below.

> Set global brnf_call_* variables to defaults in br_nf_proc_register() and
> br_nf_ipv6_proc_register() at module init instead of at variable definition
> to avoid further #ifdef CONFIG_SYSCTL constructs.
> 
> Define br_nf_ipv6_proc_register() and br_nf_ipv6_proc_unregister() to avoid
> 
> Tested with a simple bridge with two interfaces and IPv6 packets trying
> to pass from host on left side to host on right side of the bridge.
> 
> Fixes: 230ac490f7fba ("netfilter: bridge: split ipv6 code into separated file")
> 
> Signed-off-by: Bernhard Thaler <bernhard.thaler@wvnet.at>
> ---
> ---
> NOTE:
> * dependency to CONFIG_IPV6 instead of CONFIG_IP6_NF_IPTABLES would be more
>   "conservative" approach as br_netfilter_ipv6.o was introduced due to
>   dependencies in br_validate_ipv6() to CONFIG_IPV6; but CONFIG_IP6_NF_IPTABLES
>   will be needed for ip6tables so this dependency may be more "holistic"
> * CONFIG_IP6_NF_IPTABLES=n makes br_validate_ipv6() being imported from
>   br_netfilter.h; it is used in br_netfilter_hooks.c within br_nf_forward_ip()
>   and br_nf_dev_queue_xmit() and returns -1 which will lead to NF_DROP;
>   After defaulting /proc/sys/net/bridge/bridge-nf-call-ip6tables to 0 with
>   CONFIG_IP6_NF_IPTABLES=n these two functions me never see IPV6 packets and 
>   therefore this may not be a problem; I was not able to fully confirm this
> 
> Patch history
> 
> v3
> * fix checkpatch error in separate patch
> * changes to reduce #ifdef pollution
> 
> v2
> * do not expose sysfs and sysctl if CONFIG_IP6_NF_IPTABLES=n 
> * change dependency to CONFIG_IP6_NF_IPTABLES as suggested by Florian Westphal
> * removed changes to br_validate_ipv6() in br_netfilter.h as test show it may
>   not be needed
> 
> v1
> * sysfs and sysctl entry were exposed but not writeable if CONFIG_IPV6=n
>  include/net/netfilter/br_netfilter.h |   21 +++++++++-
>  net/bridge/Makefile                  |    2 +-
>  net/bridge/br_netfilter_hooks.c      |   70 ++++++++++++++++++++--------------
>  net/bridge/br_netfilter_ipv6.c       |   44 +++++++++++++++++++++
>  net/bridge/br_sysfs_br.c             |    4 ++
>  5 files changed, 111 insertions(+), 30 deletions(-)
> 
> diff --git a/include/net/netfilter/br_netfilter.h b/include/net/netfilter/br_netfilter.h
> index bab824b..e2cb715 100644
> --- a/include/net/netfilter/br_netfilter.h
> +++ b/include/net/netfilter/br_netfilter.h
> @@ -44,11 +44,17 @@ static inline struct rtable *bridge_parent_rtable(const struct net_device *dev)
>  struct net_device *setup_pre_routing(struct sk_buff *skb);
>  void br_netfilter_enable(void);
>  
> -#if IS_ENABLED(CONFIG_IPV6)
> +#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
>  int br_validate_ipv6(struct sk_buff *skb);
>  unsigned int br_nf_pre_routing_ipv6(const struct nf_hook_ops *ops,
>  				    struct sk_buff *skb,
>  				    const struct nf_hook_state *state);
> +#ifdef CONFIG_SYSCTL
> +int brnf_sysctl_call_tables(struct ctl_table *ctl, int write,
> +			    void __user *buffer, size_t *lenp, loff_t *ppos);
> +int br_nf_ipv6_proc_register(void);
> +void br_nf_ipv6_proc_unregister(void);
> +#endif
>  #else
>  static inline int br_validate_ipv6(struct sk_buff *skb)
>  {
> @@ -61,6 +67,19 @@ br_nf_pre_routing_ipv6(const struct nf_hook_ops *ops, struct sk_buff *skb,
>  {
>  	return NF_DROP;
>  }
> +
> +#ifdef CONFIG_SYSCTL
> +static inline int br_nf_ipv6_proc_register(void)
> +{
> +	return 0;
> +}
> +
> +static inline void br_nf_ipv6_proc_unregister(void)
> +{
> +}
>  #endif
> +#endif
> +
> +extern int brnf_call_ip6tables __read_mostly;
>  
>  #endif /* _BR_NETFILTER_H_ */
> diff --git a/net/bridge/Makefile b/net/bridge/Makefile
> index a1cda5d..3fd8beb 100644
> --- a/net/bridge/Makefile
> +++ b/net/bridge/Makefile
> @@ -13,7 +13,7 @@ bridge-$(CONFIG_SYSFS) += br_sysfs_if.o br_sysfs_br.o
>  bridge-$(subst m,y,$(CONFIG_BRIDGE_NETFILTER)) += br_nf_core.o
>  
>  br_netfilter-y := br_netfilter_hooks.o
> -br_netfilter-$(subst m,y,$(CONFIG_IPV6)) += br_netfilter_ipv6.o
> +br_netfilter-$(subst m,y,$(CONFIG_IP6_NF_IPTABLES)) += br_netfilter_ipv6.o
>  obj-$(CONFIG_BRIDGE_NETFILTER) += br_netfilter.o
>  
>  bridge-$(CONFIG_BRIDGE_IGMP_SNOOPING) += br_multicast.o br_mdb.o
> diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
> index 624e1f2..b202cfe 100644
> --- a/net/bridge/br_netfilter_hooks.c
> +++ b/net/bridge/br_netfilter_hooks.c
> @@ -42,24 +42,16 @@
>  #include "br_private.h"
>  #ifdef CONFIG_SYSCTL
>  #include <linux/sysctl.h>
> -#endif
>  
> -#ifdef CONFIG_SYSCTL
>  static struct ctl_table_header *brnf_sysctl_header;
> -static int brnf_call_iptables __read_mostly = 1;
> -static int brnf_call_ip6tables __read_mostly = 1;
> -static int brnf_call_arptables __read_mostly = 1;
> +#endif
> +
> +static int brnf_call_iptables __read_mostly;
> +int brnf_call_ip6tables __read_mostly;

You can move brnf_call_ip6tables to br_netfilter_ipv6, then add to the
header file this:

#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
extern int brnf_call_ip6tables;

static inline bool brnf_call_ip6tables_is_set(struct net_bridge *br)
{
        return !brnf_call_ip6tables && !br->nf_call_ip6tables;
}
#else
static inline bool brnf_call_ip6tables_is_set(struct net_bridge *br)
{
        return false;
}
#endif

from the br netfilter ipv6 header file.