bridge: Prevent insertion of FDB entry with disallowed vlan

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 <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 37 insertions, 2 deletions

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 7985deaff52f..04d6348fd530 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 06811d79f89f..59d3a85c5873 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 4a3716102789..5fee2feaf292 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.
  */