Merge branch 'bridge-egress-fixes'

Nikolay Aleksandrov says:

====================
net: bridge: vlan tunnel egress path fixes

These two fixes take care of tunnel_dst problems in the vlan tunnel egress
path. Patch 01 fixes a null ptr deref due to the lockless use of tunnel_dst
pointer without checking it first, and patch 02 fixes a use-after-free
issue due to wrong dst refcounting (dst_clone() -> dst_hold_safe()).

Both fix the same commit and should be queued for stable backports:
Fixes: 11538d0 ("bridge: vlan dst_metadata hooks in ingress and egress paths")

v2: no changes, added stable list to CC
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

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 */

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;
 }
@@ -182,20 +187,25 @@ 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);
 	err = skb_vlan_pop(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 && dst_hold_safe(&tunnel_dst->dst))
+		skb_dst_set(skb, &tunnel_dst->dst);
 
 	return 0;
 }