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);