From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16790C47086 for ; Tue, 25 May 2021 20:24:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBD0A6140B for ; Tue, 25 May 2021 20:24:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233227AbhEYUZn (ORCPT ); Tue, 25 May 2021 16:25:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:59466 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233048AbhEYUZn (ORCPT ); Tue, 25 May 2021 16:25:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id EA59E613CD; Tue, 25 May 2021 20:24:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1621974253; bh=rI509idxZaXU3p0x4ACjK1JgRUuxZjhnwyX3VTewr4g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BOWcYdtYSvlR7jsZ2AuctiKTJcvG25FFZxfCSrEc2PkA/KBrak1/g6sJ6Jhv7HTj4 k8LHPamZ9rGgE54KxYGefQhh4aC5UdYq1eHHyI9LCXEawUonvNXkffA02YFIXPUsjn O6UVddaBPpIBjw3NxMy/qID/NJD9z8DtDq6OeZ+R7mLeCkpQwtQCN6PVsm+zeO2Bc6 buvoiC/N9Tvg+NaxIRKSxyujTkrhrPtwGrHMVFRp+K9WzRHD5FNHYqxJHQHslhE+F2 TwH0azqjJ/WsWROvr8W0tviS7PDqofh1fsb6H5fmot2nRnSP7evjNrid83NVcOb7Q4 et1iRUBrkfWFQ== Date: Tue, 25 May 2021 13:24:11 -0700 From: Eric Biggers To: Boris Burkov Cc: fstests@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v4 4/4] generic: test fs-verity EFBIG scenarios Message-ID: References: <508058f805a45808764a477e9ad04353a841cf53.1620248200.git.boris@bur.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <508058f805a45808764a477e9ad04353a841cf53.1620248200.git.boris@bur.io> Precedence: bulk List-ID: X-Mailing-List: fstests@vger.kernel.org On Wed, May 05, 2021 at 02:04:46PM -0700, Boris Burkov wrote: > diff --git a/tests/generic/632 b/tests/generic/632 > new file mode 100755 > index 00000000..5a5ed576 > --- /dev/null > +++ b/tests/generic/632 > @@ -0,0 +1,86 @@ > +#! /bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# Copyright (c) 2021 Facebook, Inc. All Rights Reserved. > +# > +# FS QA Test 632 > +# > +# Test some EFBIG scenarios with very large files. > +# To create the files, use pwrite with an offset close to the > +# file system's max file size. Can you please make this comment properly describe the purpose of this test? As-is it doesn't mention that it is related to fs-verity at all, let alone to specific filesystems' implementations of fs-verity. > +max_sz=$(_get_max_file_size) > +_fsv_scratch_begin_subtest "way too big: fail on first merkle block" > +# have to go back by 4096 from max to not hit the fsverity MAX_DEPTH check. What is meant by the "fsverity MAX_DEPTH" check? > +$XFS_IO_PROG -fc "pwrite -q $(($max_sz - 4096)) 1" $fsv_file > +_fsv_enable $fsv_file |& _filter_scratch Using the "truncate" xfs_io command instead of "pwrite" would probably make more sense here, as the goal is to just create a file of a specific size. > + > +# The goal of this second test is to make a big enough file that we trip the > +# EFBIG codepath, but not so big that we hit it immediately as soon as we try > +# to write a Merkle leaf. Because of the layout of the Merkle tree that > +# fs-verity uses, this is a bit complicated to compute dynamically. > + > +# The layout of the Merkle tree has the leaf nodes last, but writes them first. > +# To get an interesting overflow, we need the start of L0 to be < MAX but the > +# end of the merkle tree (EOM) to be past MAX. Ideally, the start of L0 is only > +# just smaller than MAX, so that we don't have to write many blocks to blow up. > + > +# 0 EOF round-to-64k L7L6L5 L4 L3 L2 L1 L0 MAX EOM > +# |-------------------------| ||-|--|---|----|-----|------|--|!!!!!| > + > +# Given this structure, we can compute the size of the file that yields the > +# desired properties: > +# sz + 64k + sz/128^8 + sz/128^7 + ... + sz/128^2 < MAX > +# (128^8)sz + (128^8)64k + sz + (128)sz + (128^2)sz + ... + (128^6)sz < (128^8)MAX > +# sz(128^8 + 128^6 + 128^5 + 128^4 + 128^3 + 128^2 + 128 + 1) < (128^8)(MAX - 64k) > +# sz < (128^8/(128^8 + (128^6 + ... 1))(MAX - 64k) > +# > +# Do the actual caclulation with 'bc' and 20 digits of precision. This calculation isn't completely accurate because it doesn't round the levels to a block boundary. Nor does it consider that the 64K is an alignment rather than a fixed amount added. But for the test you don't need the absolute largest file whose level 1 doesn't exceed the limit, but rather just one almost that large. So it would be okay to add 64K as a fixed amount, along with 4K for every level on top of the 'sz/128^(level+1)' you already have, to get an over-estimate of the amount of extra space needed to cache the Merkle tree. But please make it clear that it's an over-estimate, and hence an under-estimate of the file size desired for the test. Also please document that this is all assuming SHA-256 with 4K blocks, and also that the maximum file size is assumed to fit in 64 bits; hence the consideration of 8 levels is sufficient. - Eric