Subject: Re: [PATCH net] bridge: Prevent insertion of FDB entry with disallowed vlan

From: Vlad Yasevich <[email-masked]>
Date: Wed, 28 May 2014 10:02:05 -0400

On 05/26/2014 02:15 AM, Toshiaki Makita wrote:
> br_handle_local_finish() is allowing us to insert an FDB entry with
> disallowed vlan. For example, when port 1 and 2 are communicating in
> vlan 10, and even if vlan 10 is disallowed on port 3, port 3 can
> interfere with their communication by spoofed src mac address with
> vlan id 10.
> 
> Note: Even if it is judged that a frame should not be learned, it should
> not be dropped because it is destined for not forwarding layer but higher
> layer. See IEEE 802.1Q-2011 8.13.10.
> 
> Signed-off-by: Toshiaki Makita <[email-masked]>
> ---
>  net/bridge/br_input.c   |  4 ++--
>  net/bridge/br_private.h |  7 +++++++
>  net/bridge/br_vlan.c    | 28 ++++++++++++++++++++++++++++
>  3 files changed, 37 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index 7985dea..04d6348 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -147,8 +147,8 @@ static int br_handle_local_finish(struct sk_buff *skb)
>  	struct net_bridge_port *p = br_port_get_rcu(skb->dev);
>  	u16 vid = 0;
>  
> -	br_vlan_get_tag(skb, &vid);
> -	if (p->flags & BR_LEARNING)
> +	/* check if vlan is allowed, to avoid spoofing */
> +	if (p->flags & BR_LEARNING && br_should_learn(p, skb, &vid))
>  		br_fdb_update(p->br, p, eth_hdr(skb)->h_source, vid, false);
>  	return 0;	 /* process further */
>  }
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 06811d7..59d3a85 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -581,6 +581,7 @@ bool br_allowed_ingress(struct net_bridge *br, struct net_port_vlans *v,
>  			struct sk_buff *skb, u16 *vid);
>  bool br_allowed_egress(struct net_bridge *br, const struct net_port_vlans *v,
>  		       const struct sk_buff *skb);
> +bool br_should_learn(struct net_bridge_port *p, struct sk_buff *skb, u16 *vid);
>  struct sk_buff *br_handle_vlan(struct net_bridge *br,
>  			       const struct net_port_vlans *v,
>  			       struct sk_buff *skb);
> @@ -648,6 +649,12 @@ static inline bool br_allowed_egress(struct net_bridge *br,
>  	return true;
>  }
>  
> +static inline bool br_should_learn(struct net_bridge_port *p,
> +				   struct sk_buff *skb, u16 *vid)
> +{
> +	return true;
> +}
> +
>  static inline struct sk_buff *br_handle_vlan(struct net_bridge *br,
>  					     const struct net_port_vlans *v,
>  					     struct sk_buff *skb)
> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> index 4a37161..5fee2fe 100644
> --- a/net/bridge/br_vlan.c
> +++ b/net/bridge/br_vlan.c
> @@ -241,6 +241,34 @@ bool br_allowed_egress(struct net_bridge *br,
>  	return false;
>  }
>  
> +/* Called under RCU */
> +bool br_should_learn(struct net_bridge_port *p, struct sk_buff *skb, u16 *vid)
> +{
> +	struct net_bridge *br = p->br;
> +	struct net_port_vlans *v;
> +
> +	if (!br->vlan_enabled)
> +		return true;
> +
> +	v = rcu_dereference(p->vlan_info);
> +	if (!v)
> +		return false;
> +
> +	br_vlan_get_tag(skb, vid);
> +	if (!*vid) {
> +		*vid = br_get_pvid(v);
> +		if (*vid == VLAN_N_VID)
> +			return false;
> +
> +		return true;
> +	}
> +
> +	if (test_bit(*vid, v->vlan_bitmap))
> +		return true;
> +
> +	return false;
> +}
> +
>  /* Must be protected by RTNL.
>   * Must be called with vid in range from 1 to 4094 inclusive.
>   */
> 

This is very similar to br_allow_ingress(), so may be you can
re-factor so that we only have 1 such function...

-vlad