diff --git a/fs/smb/client/cifsacl.c b/fs/smb/client/cifsacl.c
index 12005f46307d..213a421bf8e9 100644
--- a/fs/smb/client/cifsacl.c
+++ b/fs/smb/client/cifsacl.c
@@ -100,8 +100,23 @@ cifs_idmap_key_destroy(struct key *key)
 		kfree(key->payload.data[0]);
 }
 
+static int
+cifs_idmap_key_vet_description(const char *description)
+{
+	/*
+	 * cifs.idmap descriptions are authority-bearing inputs to the
+	 * cifs.idmap upcall helper.  Only allow the kernel to create this
+	 * type of key using the private root_cred installed in
+	 * init_cifs_idmap; reject userspace request_key(2)/add_key(2).
+	 */
+	if (current_cred() != root_cred)
+		return -EPERM;
+	return 0;
+}
+
 static struct key_type cifs_idmap_key_type = {
 	.name        = "cifs.idmap",
+	.vet_description = cifs_idmap_key_vet_description,
 	.instantiate = cifs_idmap_key_instantiate,
 	.destroy     = cifs_idmap_key_destroy,
 	.describe    = user_describe,