net: sk_{detach|attach}_filter() rcu fixes

sk_attach_filter() and sk_detach_filter() are run with socket locked.

Use the appropriate rcu_dereference_protected() instead of blocking BH,
and rcu_dereference_bh().
There is no point adding BH prevention and memory barrier.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -638,10 +638,9 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 		return err;
 	}
 
-	rcu_read_lock_bh();
-	old_fp = rcu_dereference_bh(sk->sk_filter);
+	old_fp = rcu_dereference_protected(sk->sk_filter,
+					   sock_owned_by_user(sk));
 	rcu_assign_pointer(sk->sk_filter, fp);
-	rcu_read_unlock_bh();
 
 	if (old_fp)
 		sk_filter_delayed_uncharge(sk, old_fp);
@@ -654,14 +653,13 @@ int sk_detach_filter(struct sock *sk)
 	int ret = -ENOENT;
 	struct sk_filter *filter;
 
-	rcu_read_lock_bh();
-	filter = rcu_dereference_bh(sk->sk_filter);
+	filter = rcu_dereference_protected(sk->sk_filter,
+					   sock_owned_by_user(sk));
 	if (filter) {
 		rcu_assign_pointer(sk->sk_filter, NULL);
 		sk_filter_delayed_uncharge(sk, filter);
 		ret = 0;
 	}
-	rcu_read_unlock_bh();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(sk_detach_filter);