netlink: Do not schedule work from sk_destruct

It is wrong to schedule a work from sk_destruct using the socket
as the memory reserve because the socket will be freed immediately
after the return from sk_destruct.

Instead we should do the deferral prior to sk_free.

This patch does just that.

Fixes: 707693c8a4 ("netlink: Call cb->done from a worker thread")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -322,11 +322,13 @@ static void netlink_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
 	sk_mem_charge(sk, skb->truesize);
 }
 
-static void __netlink_sock_destruct(struct sock *sk)
+static void netlink_sock_destruct(struct sock *sk)
 {
 	struct netlink_sock *nlk = nlk_sk(sk);
 
 	if (nlk->cb_running) {
+		if (nlk->cb.done)
+			nlk->cb.done(&nlk->cb);
 		module_put(nlk->cb.module);
 		kfree_skb(nlk->cb.skb);
 	}
@@ -348,21 +350,7 @@ static void netlink_sock_destruct_work(struct work_struct *work)
 	struct netlink_sock *nlk = container_of(work, struct netlink_sock,
 						work);
 
-	nlk->cb.done(&nlk->cb);
+	sk_free(&nlk->sk);
-	__netlink_sock_destruct(&nlk->sk);
-}
-
-static void netlink_sock_destruct(struct sock *sk)
-{
-	struct netlink_sock *nlk = nlk_sk(sk);
-
-	if (nlk->cb_running && nlk->cb.done) {
-		INIT_WORK(&nlk->work, netlink_sock_destruct_work);
-		schedule_work(&nlk->work);
-		return;
-	}
-
-	__netlink_sock_destruct(sk);
 }
 
 /* This lock without WQ_FLAG_EXCLUSIVE is good on UP and it is _very_ bad on
@@ -667,8 +655,18 @@ out_module:
 static void deferred_put_nlk_sk(struct rcu_head *head)
 {
 	struct netlink_sock *nlk = container_of(head, struct netlink_sock, rcu);
+	struct sock *sk = &nlk->sk;
 
-	sock_put(&nlk->sk);
+	if (!atomic_dec_and_test(&sk->sk_refcnt))
+		return;
+
+	if (nlk->cb_running && nlk->cb.done) {
+		INIT_WORK(&nlk->work, netlink_sock_destruct_work);
+		schedule_work(&nlk->work);
+		return;
+	}
+
+	sk_free(sk);
 }
 
 static int netlink_release(struct socket *sock)