From: Greg KH [mailto:gregkh@linuxfoundation.org]
Sent: Sunday, June 27, 2021 12:56 PM
On Fri, Jun 25, 2021 at 06:56:06PM +0200, Roberto Sassu wrote:

quoted

+++ b/security/integrity/digest_lists/digest_lists.h

@@ -0,0 +1,117 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2005,2006,2007,2008 IBM Corporation
+ * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ *
+ * File: digest_lists.h
+ *      Unexported definitions for digest lists.

Unexported to whom?

Hi Greg

I meant not placed in include/linux.

quoted

+ */
+
+#ifndef __DIGEST_LISTS_INTERNAL_H
+#define __DIGEST_LISTS_INTERNAL_H
+
+#include <linux/types.h>
+#include <linux/crypto.h>
+#include <linux/fs.h>
+#include <linux/security.h>
+#include <linux/hash.h>
+#include <linux/tpm.h>
+#include <linux/audit.h>
+#include <crypto/hash_info.h>
+#include <linux/hash_info.h>
+#include <uapi/linux/digest_lists.h>
+
+#define MAX_DIGEST_SIZE	64
+#define HASH_BITS 10
+#define MEASURE_HTABLE_SIZE (1 << HASH_BITS)
+
+struct digest_list_item {
+	loff_t size;
+	u8 *buf;
+	u8 actions;
+	u8 digest[64];
+	enum hash_algo algo;
+	const char *label;
+};
+
+struct digest_list_item_ref {
+	struct digest_list_item *digest_list;
+	loff_t digest_offset;
+	loff_t hdr_offset;
+};
+
+struct digest_item {
+	/* hash table pointers */
+	struct hlist_node hnext;
+	/* digest list references (protected by RCU) */
+	struct digest_list_item_ref *refs;
+};
+
+struct h_table {
+	atomic_long_t len;

Why is this atomic?  Why would that matter?

Yes, it shouldn't be. There are not concurrent updates.

quoted

+	struct hlist_head queue[MEASURE_HTABLE_SIZE];
+};
+
+static inline unsigned int hash_key(u8 *digest)
+{
+	return (digest[0] | digest[1] << 8) % MEASURE_HTABLE_SIZE;
+}

Don't we have hashing functions in the kernel already?

We had a discussion before:

https://lore.kernel.org/linux-integrity/1587739544.5190.14.camel@linux.ibm.com/ (local)

It seems there is no real advantage in hashing a digest.

quoted

+
+static inline struct compact_list_hdr *get_hdr(
+					struct digest_list_item *digest_list,
+					loff_t hdr_offset)
+{
+	return (struct compact_list_hdr *)(digest_list->buf + hdr_offset);
+}

pointer math feels rough, are you shure you want to do this this way?

Maybe, I could change digest_list_item_ref to:

struct digest_list_item_ref {
	struct digest_list_item *digest_list;
	u8 *digest;
	struct compact_list_hdr *hdr;
};

where digest and hdr are calculated in the same way.

Or you have a different suggestion?

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

thanks,

greg k-h