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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96A0AC001DE for ; Wed, 19 Jul 2023 14:24:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231564AbjGSOYd (ORCPT ); Wed, 19 Jul 2023 10:24:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231250AbjGSOY2 (ORCPT ); Wed, 19 Jul 2023 10:24:28 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4C2F2690; Wed, 19 Jul 2023 07:24:08 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4R5dJQ0gzxzNmKd; Wed, 19 Jul 2023 22:20:22 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by kwepemm600013.china.huawei.com (7.193.23.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Wed, 19 Jul 2023 22:23:40 +0800 Subject: Re: [RFC PATCH 05/21] ubifs: Pass worst-case buffer size to compression routines To: Ard Biesheuvel , Eric Biggers CC: , Herbert Xu , Kees Cook , Haren Myneni , Nick Terrell , Minchan Kim , Sergey Senozhatsky , Jens Axboe , Giovanni Cabiddu , Richard Weinberger , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Steffen Klassert , , , , , , References: <20230718125847.3869700-1-ardb@kernel.org> <20230718125847.3869700-6-ardb@kernel.org> <20230718223813.GC1005@sol.localdomain> From: Zhihao Cheng Message-ID: <3330004f-acac-81b4-e382-a17221a0a128@huawei.com> Date: Wed, 19 Jul 2023 22:23:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 在 2023/7/19 16:33, Ard Biesheuvel 写道: > On Wed, 19 Jul 2023 at 00:38, Eric Biggers wrote: >> >> On Tue, Jul 18, 2023 at 02:58:31PM +0200, Ard Biesheuvel wrote: >>> Currently, the ubifs code allocates a worst case buffer size to >>> recompress a data node, but does not pass the size of that buffer to the >>> compression code. This means that the compression code will never use I think you mean the 'out_len' which describes the lengh of 'buf' is passed into ubifs_decompress, which effects the result of decompressor(eg. lz4 uses length to calculate the buffer end pos). So, we should pass the real lenghth of 'buf'. Reviewed-by: Zhihao Cheng >>> the additional space, and might fail spuriously due to lack of space. >>> >>> So let's multiply out_len by WORST_COMPR_FACTOR after allocating the >>> buffer. Doing so is guaranteed not to overflow, given that the preceding >>> kmalloc_array() call would have failed otherwise. >>> >>> Signed-off-by: Ard Biesheuvel >>> --- >>> fs/ubifs/journal.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/fs/ubifs/journal.c b/fs/ubifs/journal.c >>> index dc52ac0f4a345f30..4e5961878f336033 100644 >>> --- a/fs/ubifs/journal.c >>> +++ b/fs/ubifs/journal.c >>> @@ -1493,6 +1493,8 @@ static int truncate_data_node(const struct ubifs_info *c, const struct inode *in >>> if (!buf) >>> return -ENOMEM; >>> >>> + out_len *= WORST_COMPR_FACTOR; >>> + >>> dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ; >>> data_size = dn_size - UBIFS_DATA_NODE_SZ; >>> compr_type = le16_to_cpu(dn->compr_type); >> >> This looks like another case where data that would be expanded by compression >> should just be stored uncompressed instead. >> >> In fact, it seems that UBIFS does that already. ubifs_compress() has this: >> >> /* >> * If the data compressed only slightly, it is better to leave it >> * uncompressed to improve read speed. >> */ >> if (in_len - *out_len < UBIFS_MIN_COMPRESS_DIFF) >> goto no_compr; >> >> So it's unclear why the WORST_COMPR_FACTOR thing is needed at all. >> > > It is not. The buffer is used for decompression in the truncation > path, so none of this logic even matters. Even if the subsequent > recompression of the truncated data node could result in expansion > beyond the uncompressed size of the original data (which seems > impossible to me), increasing the size of this buffer would not help > as it is the input buffer for the compression not the output buffer. > . >