net/sched: act_tunnel_key: fix memory leak in case of action replace

running the following TDC test cases:

 7afc - Replace tunnel_key set action with all parameters
 364d - Replace tunnel_key set action with all parameters and cookie

it's possible to trigger kmemleak warnings like:

  unreferenced object 0xffff94797127ab40 (size 192):
  comm "tc", pid 3248, jiffies 4300565293 (age 1006.862s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 c0 93 f9 8a ff ff ff ff  ................
    41 84 ee 89 ff ff ff ff 00 00 00 00 00 00 00 00  A...............
  backtrace:
    [<000000001e85b61c>] tunnel_key_init+0x31d/0x820 [act_tunnel_key]
    [<000000007f3f6ee7>] tcf_action_init_1+0x384/0x4c0
    [<00000000e89e3ded>] tcf_action_init+0x12b/0x1a0
    [<00000000c1c8c0f8>] tcf_action_add+0x73/0x170
    [<0000000095a9fc28>] tc_ctl_action+0x122/0x160
    [<000000004bebeac5>] rtnetlink_rcv_msg+0x263/0x2d0
    [<000000009fd862dd>] netlink_rcv_skb+0x4a/0x110
    [<00000000b55199e7>] netlink_unicast+0x1a0/0x250
    [<000000004996cd21>] netlink_sendmsg+0x2c1/0x3c0
    [<000000004d6a94b4>] sock_sendmsg+0x36/0x40
    [<000000005d9f0208>] ___sys_sendmsg+0x280/0x2f0
    [<00000000dec19023>] __sys_sendmsg+0x5e/0xa0
    [<000000004b82ac81>] do_syscall_64+0x5b/0x180
    [<00000000a0f1209a>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
    [<000000002926b2ab>] 0xffffffffffffffff

when the tunnel_key action is replaced, the kernel forgets to release the
dst metadata: ensure they are released by tunnel_key_init(), the same way
it's done in tunnel_key_release().

Fixes: d0f6dd8a ("net/sched: Introduce act_tunnel_key")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_tunnel_key.c

@@ -197,6 +197,15 @@ static const struct nla_policy tunnel_key_policy[TCA_TUNNEL_KEY_MAX + 1] = {
 	[TCA_TUNNEL_KEY_ENC_TTL]      = { .type = NLA_U8 },
 };
 
+static void tunnel_key_release_params(struct tcf_tunnel_key_params *p)
+{
+	if (!p)
+		return;
+	if (p->tcft_action == TCA_TUNNEL_KEY_ACT_SET)
+		dst_release(&p->tcft_enc_metadata->dst);
+	kfree_rcu(p, rcu);
+}
+
 static int tunnel_key_init(struct net *net, struct nlattr *nla,
 			   struct nlattr *est, struct tc_action **a,
 			   int ovr, int bind, bool rtnl_held,
@@ -360,8 +369,7 @@ static int tunnel_key_init(struct net *net, struct nlattr *nla,
 	rcu_swap_protected(t->params, params_new,
 			   lockdep_is_held(&t->tcf_lock));
 	spin_unlock_bh(&t->tcf_lock);
-	if (params_new)
-		kfree_rcu(params_new, rcu);
+	tunnel_key_release_params(params_new);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -385,12 +393,7 @@ static void tunnel_key_release(struct tc_action *a)
 	struct tcf_tunnel_key_params *params;
 
 	params = rcu_dereference_protected(t->params, 1);
-	if (params) {
-		if (params->tcft_action == TCA_TUNNEL_KEY_ACT_SET)
-			dst_release(&params->tcft_enc_metadata->dst);
-
-		kfree_rcu(params, rcu);
-	}
+	tunnel_key_release_params(params);
 }
 
 static int tunnel_key_geneve_opts_dump(struct sk_buff *skb,