From patchwork Wed Jan 11 20:47:39 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 13097225 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76937C5479D for ; Wed, 11 Jan 2023 20:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230047AbjAKUsw (ORCPT ); Wed, 11 Jan 2023 15:48:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229539AbjAKUsv (ORCPT ); Wed, 11 Jan 2023 15:48:51 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D26D05FF8; Wed, 11 Jan 2023 12:48:48 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6B36C61E53; Wed, 11 Jan 2023 20:48:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF39EC433EF; Wed, 11 Jan 2023 20:48:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673470127; bh=HzsRQDLfFJisGLIvMqbnFWr06oooTi1mp0LWzSJqKEE=; h=From:To:Cc:Subject:Date:From; b=K2UO6+TFqKzTTio+chMxCyja8QqE3Mr2PTwbJfLvBYXiQltWFHfx3cdbrXlTii5na f68CvFomlhYRO4iu75kg7/YDtk/n7lE8NBmsJXlm4uKY4UcSVUbrxxQuOcMMymCw/J UrjSn3Z4Uth6aHXFJbDPhyRXK2guCqy5kDqyJwEuF2qje9khBEevkzVXVOKikwNOwL YdOGFcXvvscQKVvMLlSS/wvrHtcWN6yLLFQtfeiHqUkzAt62FJmf2T+Shj0dlfDmbf omMdD4KtntdzM0RIc28LAIfKgROdoYssadikI4i51EY63gPWrGasLPONN2IhXYO43a 3OFKVXmnw92QQ== From: Eric Biggers To: fstests@vger.kernel.org Cc: linux-fscrypt@vger.kernel.org, Ojaswin Mujoo Subject: [PATCH v2] generic/692: generalize the test for non-4K Merkle tree block sizes Date: Wed, 11 Jan 2023 12:47:39 -0800 Message-Id: <20230111204739.77828-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fscrypt@vger.kernel.org From: Ojaswin Mujoo Due to the assumption of the Merkle tree block size being 4K, the file size calculated for the second test case was taking way too long to hit EFBIG in case of larger block sizes like 64K. Fix this by generalizing the calculation to any Merkle tree block size >= 1K. Signed-off-by: Ojaswin Mujoo Co-developed-by: Eric Biggers Signed-off-by: Eric Biggers --- v2: Cleaned up the original patch from Ojaswin: - Explained the calculations as they are done. - Considered 11 levels instead of 8, to account for 1K blocks potentially needing up to 11 levels. - Increased 'scale' for real number results, and don't use 'scale' at all for integer number results. - Improved a variable name. - Updated commit message. tests/generic/692 | 37 +++++++++++++++++++++++++------------ 1 file changed, 25 insertions(+), 12 deletions(-) diff --git a/tests/generic/692 b/tests/generic/692 index d6da734b..90832b16 100755 --- a/tests/generic/692 +++ b/tests/generic/692 @@ -51,18 +51,31 @@ _fsv_enable $fsv_file |& _filter_scratch # # The Merkle tree is stored with the leaf node level (L0) last, but it is # written first. To get an interesting overflow, we need the maximum file size -# (MAX) to be in the middle of L0 -- ideally near the beginning of L0 so that we -# don't have to write many blocks before getting an error. -# -# With SHA-256 and 4K blocks, there are 128 hashes per block. Thus, ignoring -# padding, L0 is 1/128 of the file size while the other levels in total are -# 1/128**2 + 1/128**3 + 1/128**4 + ... = 1/16256 of the file size. So still -# ignoring padding, for L0 start exactly at MAX, the file size must be s such -# that s + s/16256 = MAX, i.e. s = MAX * (16256/16257). Then to get a file size -# where MAX occurs *near* the start of L0 rather than *at* the start, we can -# just subtract an overestimate of the padding: 64K after the file contents, -# then 4K per level, where the consideration of 8 levels is sufficient. -sz=$(echo "scale=20; $max_sz * (16256/16257) - 65536 - 4096*8" | $BC -q | cut -d. -f1) +# ($max_sz) to be in the middle of L0 -- ideally near the beginning of L0 so +# that we don't have to write many blocks before getting an error. + +bs=$FSV_BLOCK_SIZE +hash_size=32 # SHA-256 +hash_per_block=$(echo "scale=30; $bs/($hash_size)" | $BC -q) + +# Compute the proportion of the original file size that the non-leaf levels of +# the Merkle tree take up. Ignoring padding, this is 1/${hashes_per_block}^2 + +# 1/${hashes_per_block}^3 + 1/${hashes_per_block}^4 + ... Compute it using the +# formula for the sum of a geometric series: \sum_{k=0}^{\infty} ar^k = a/(1-r). +a=$(echo "scale=30; 1/($hash_per_block^2)" | $BC -q) +r=$(echo "scale=30; 1/$hash_per_block" | $BC -q) +nonleaves_relative_size=$(echo "scale=30; $a/(1-$r)" | $BC -q) + +# Compute the original file size where the leaf level L0 starts at $max_sz. +# Padding is still ignored, so the real value is slightly smaller than this. +sz=$(echo "$max_sz/(1+$nonleaves_relative_size)" | $BC -q) + +# Finally, to get a file size where $max_sz occurs just after the start of L0 +# rather than *at* the start of L0, subtract an overestimate of the padding: 64K +# after the file contents, then $bs per level for 11 levels. 11 levels is the +# most levels that can ever be needed, assuming the block size is at least 1K. +sz=$(echo "$sz - 65536 - $bs*11" | $BC -q) + _fsv_scratch_begin_subtest "still too big: fail on first invalid merkle block" truncate -s $sz $fsv_file _fsv_enable $fsv_file |& _filter_scratch