selinux: implement mmap on /selinux/policy

/selinux/policy allows a user to copy the policy back out of the kernel.
This patch allows userspace to actually mmap that file and use it directly.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 7565d16..3a1739b 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -3169,7 +3169,7 @@
 
 	*len = security_policydb_len();
 
-	*data = vmalloc(*len);
+	*data = vmalloc_user(*len);
 	if (!*data)
 		return -ENOMEM;