net: bridge: fix vlan tunnel dst null pointer dereference

This patch fixes a tunnel_dst null pointer dereference due to lockless
access in the tunnel egress path. When deleting a vlan tunnel the
tunnel_dst pointer is set to NULL without waiting a grace period (i.e.
while it's still usable) and packets egressing are dereferencing it
without checking. Use READ/WRITE_ONCE to annotate the lockless use of
tunnel_id, use RCU for accessing tunnel_dst and make sure it is read
only once and checked in the egress path. The dst is already properly RCU
protected so we don't need to do anything fancy than to make sure
tunnel_id and tunnel_dst are read only once and checked in the egress path.

Cc: stable@vger.kernel.org
Fixes: 11538d039ac6 ("bridge: vlan dst_metadata hooks in ingress and egress paths")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 7ce8a77cc6b6b604e7587dafb5b450fae8991b73..e013d33f1c7cae0e627c126456f51b3f111a4b82 100644 (file)
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -90,8 +90,8 @@ struct bridge_mcast_stats {
 #endif
 
 struct br_tunnel_info {
-       __be64                  tunnel_id;
-       struct metadata_dst     *tunnel_dst;
+       __be64                          tunnel_id;
+       struct metadata_dst __rcu       *tunnel_dst;
 };
 
 /* private vlan flags */

diff --git a/net/bridge/br_vlan_tunnel.c b/net/bridge/br_vlan_tunnel.c
index 0d3a8c01552ee4b4bf1efc178d892a408610fee5..03de461a0d44af7e4ca89ac4a2e11754137018a1 100644 (file)
--- a/net/bridge/br_vlan_tunnel.c
+++ b/net/bridge/br_vlan_tunnel.c
@@ -41,26 +41,33 @@ static struct net_bridge_vlan *br_vlan_tunnel_lookup(struct rhashtable *tbl,
                                      br_vlan_tunnel_rht_params);
 }
 
+static void vlan_tunnel_info_release(struct net_bridge_vlan *vlan)
+{
+       struct metadata_dst *tdst = rtnl_dereference(vlan->tinfo.tunnel_dst);
+
+       WRITE_ONCE(vlan->tinfo.tunnel_id, 0);
+       RCU_INIT_POINTER(vlan->tinfo.tunnel_dst, NULL);
+       dst_release(&tdst->dst);
+}
+
 void vlan_tunnel_info_del(struct net_bridge_vlan_group *vg,
                          struct net_bridge_vlan *vlan)
 {
-       if (!vlan->tinfo.tunnel_dst)
+       if (!rcu_access_pointer(vlan->tinfo.tunnel_dst))
                return;
        rhashtable_remove_fast(&vg->tunnel_hash, &vlan->tnode,
                               br_vlan_tunnel_rht_params);
-       vlan->tinfo.tunnel_id = 0;
-       dst_release(&vlan->tinfo.tunnel_dst->dst);
-       vlan->tinfo.tunnel_dst = NULL;
+       vlan_tunnel_info_release(vlan);
 }
 
 static int __vlan_tunnel_info_add(struct net_bridge_vlan_group *vg,
                                  struct net_bridge_vlan *vlan, u32 tun_id)
 {
-       struct metadata_dst *metadata = NULL;
+       struct metadata_dst *metadata = rtnl_dereference(vlan->tinfo.tunnel_dst);
        __be64 key = key32_to_tunnel_id(cpu_to_be32(tun_id));
        int err;
 
-       if (vlan->tinfo.tunnel_dst)
+       if (metadata)
                return -EEXIST;
 
        metadata = __ip_tun_set_dst(0, 0, 0, 0, 0, TUNNEL_KEY,
@@ -69,8 +76,8 @@ static int __vlan_tunnel_info_add(struct net_bridge_vlan_group *vg,
                return -EINVAL;
 
        metadata->u.tun_info.mode |= IP_TUNNEL_INFO_TX | IP_TUNNEL_INFO_BRIDGE;
-       vlan->tinfo.tunnel_dst = metadata;
-       vlan->tinfo.tunnel_id = key;
+       rcu_assign_pointer(vlan->tinfo.tunnel_dst, metadata);
+       WRITE_ONCE(vlan->tinfo.tunnel_id, key);
 
        err = rhashtable_lookup_insert_fast(&vg->tunnel_hash, &vlan->tnode,
                                            br_vlan_tunnel_rht_params);
@@ -79,9 +86,7 @@ static int __vlan_tunnel_info_add(struct net_bridge_vlan_group *vg,
 
        return 0;
 out:
-       dst_release(&vlan->tinfo.tunnel_dst->dst);
-       vlan->tinfo.tunnel_dst = NULL;
-       vlan->tinfo.tunnel_id = 0;
+       vlan_tunnel_info_release(vlan);
 
        return err;
 }
@@ -182,12 +187,15 @@ int br_handle_ingress_vlan_tunnel(struct sk_buff *skb,
 int br_handle_egress_vlan_tunnel(struct sk_buff *skb,
                                 struct net_bridge_vlan *vlan)
 {
+       struct metadata_dst *tunnel_dst;
+       __be64 tunnel_id;
        int err;
 
-       if (!vlan || !vlan->tinfo.tunnel_id)
+       if (!vlan)
                return 0;
 
-       if (unlikely(!skb_vlan_tag_present(skb)))
+       tunnel_id = READ_ONCE(vlan->tinfo.tunnel_id);
+       if (!tunnel_id || unlikely(!skb_vlan_tag_present(skb)))
                return 0;
 
        skb_dst_drop(skb);
@@ -195,7 +203,9 @@ int br_handle_egress_vlan_tunnel(struct sk_buff *skb,
        if (err)
                return err;
 
-       skb_dst_set(skb, dst_clone(&vlan->tinfo.tunnel_dst->dst));
+       tunnel_dst = rcu_dereference(vlan->tinfo.tunnel_dst);
+       if (tunnel_dst)
+               skb_dst_set(skb, dst_clone(&tunnel_dst->dst));
 
        return 0;
 }