Revert "socket, bpf: fix possible use after free"

This reverts commit 02f7e41, which was
commit 02f7e41 upstream

Turns out the backport to 4.9 was broken.

Reported-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/core/filter.c

@@ -937,31 +937,20 @@ void sk_filter_uncharge(struct sock *sk, struct sk_filter *fp)
 /* try to charge the socket memory if there is space available
  * return true on success
  */
-static bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)
+bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
 {
 	u32 filter_size = bpf_prog_size(fp->prog->len);
 
 	/* same check as in sock_kmalloc() */
 	if (filter_size <= sysctl_optmem_max &&
 	    atomic_read(&sk->sk_omem_alloc) + filter_size < sysctl_optmem_max) {
+		atomic_inc(&fp->refcnt);
 		atomic_add(filter_size, &sk->sk_omem_alloc);
 		return true;
 	}
 	return false;
 }
 
-bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
-{
-	if (!atomic_inc_not_zero(&fp->refcnt))
-		return false;
-
-	if (!__sk_filter_charge(sk, fp)) {
-		sk_filter_release(fp);
-		return false;
-	}
-	return true;
-}
-
 static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp)
 {
 	struct sock_filter *old_prog;

net/core/sock.c

@@ -1528,16 +1528,13 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 		sock_reset_flag(newsk, SOCK_DONE);
 		skb_queue_head_init(&newsk->sk_error_queue);
 
-		rcu_read_lock();
-		filter = rcu_dereference(sk->sk_filter);
+		filter = rcu_dereference_protected(newsk->sk_filter, 1);
 		if (filter != NULL)
 			/* though it's an empty new sock, the charging may fail
 			 * if sysctl_optmem_max was changed between creation of
 			 * original socket and cloning
 			 */
 			is_charged = sk_filter_charge(newsk, filter);
-		RCU_INIT_POINTER(newsk->sk_filter, filter);
-		rcu_read_unlock();
 
 		if (unlikely(!is_charged || xfrm_sk_clone_policy(newsk, sk))) {
 			/* We need to make sure that we don't uncharge the new