selinux: fix potential counting error in avc_add_xperms_decision()

The count increases only when a node is successfully added to
the linked list.

Cc: stable@vger.kernel.org
Fixes: fa1aa143 ("selinux: extended permissions for ioctls")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/avc.c

@@ -330,12 +330,12 @@ static int avc_add_xperms_decision(struct avc_node *node,
 {
 	struct avc_xperms_decision_node *dest_xpd;
 
-	node->ae.xp_node->xp.len++;
 	dest_xpd = avc_xperms_decision_alloc(src->used);
 	if (!dest_xpd)
 		return -ENOMEM;
 	avc_copy_xperms_decision(&dest_xpd->xpd, src);
 	list_add(&dest_xpd->xpd_list, &node->ae.xp_node->xpd_head);
+	node->ae.xp_node->xp.len++;
 	return 0;
 }