From: Gao Xiang <hsiangkao@aol.com> To: Matthew Wilcox <willy@infradead.org> Cc: Gao Xiang <gaoxiang25@huawei.com>, Dave Chinner <david@fromorbit.com>, Goldwyn Rodrigues <RGoldwyn@suse.com>, "hch@lst.de" <hch@lst.de>, "darrick.wong@oracle.com" <darrick.wong@oracle.com>, "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>, "ruansy.fnst@cn.fujitsu.com" <ruansy.fnst@cn.fujitsu.com>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>, linux-erofs@lists.ozlabs.org, miaoxie@huawei.com Subject: Re: [PATCH 10/13] iomap: use a function pointer for dio submits Date: Sat, 10 Aug 2019 07:45:59 +0800 [thread overview] Message-ID: <20190809234554.GA25734@hsiangkao-HP-ZHAN-66-Pro-G1> (raw) In-Reply-To: <20190809204517.GR5482@bombadil.infradead.org> Hi Willy, On Fri, Aug 09, 2019 at 01:45:17PM -0700, Matthew Wilcox wrote: > On Wed, Aug 07, 2019 at 10:49:36PM -0700, Eric Biggers wrote: > > On Thu, Aug 08, 2019 at 12:26:42PM +0800, Gao Xiang wrote: > > > 1. decrypt->verity->decompress > > > > > > 2. verity->decompress->decrypt > > > > > > 3. decompress->decrypt->verity > > > > > > 1. and 2. could cause less computation since it processes > > > compressed data, and the security is good enough since > > > the behavior of decompression algorithm is deterministic. > > > 3 could cause more computation. > > > > > > All I want to say is the post process is so complicated since we have > > > many selection if encryption, decompression, verification are all involved. > > > > > > Maybe introduce a core subset to IOMAP is better for long-term > > > maintainment and better performance. And we should consider it > > > more carefully. > > > > > > > FWIW, the only order that actually makes sense is decrypt->decompress->verity. > > That used to be true, but a paper in 2004 suggested it's not true. > Further work in this space in 2009 based on block ciphers: > https://arxiv.org/pdf/1009.1759 > > It looks like it'd be computationally expensive to do, but feasible. Yes, maybe someone cares where encrypt is at due to their system design. and I thought over these days, I have to repeat my thought of verity again :( the meaningful order ought to be "decrypt->verity->decompress" rather than "decrypt->decompress->verity" if compression is involved. since most (de)compress algorithms are complex enough (allocate memory and do a lot of unsafe stuffes such as wildcopy) and even maybe unsafe by its design, we cannot do verity in the end for security consideration thus the whole system can be vulnerable by this order from malformed on-disk data. In other words, we need to verify on compressed data. Fsverity is fine for me since most decrypt algorithms is stable and reliable and no compression by its design, but if some decrypt software algorithms is complicated enough, I'd suggest "verity->decrypt" as well to some extent. Considering transformation "A->B->C->D->....->verity", if any of "A->B->C ->D->..." is attacked by the malformed on-disk data... It would crash or even root the whole operating system. All in all, we have to verify data earlier in order to get trusted data for later complex transformation chains. The performance benefit I described in my previous email, it seems no need to say again... please take them into consideration and I think it's no easy to get a unique generic post-read order for all real systems. Thanks, Gao Xiang > > > Decrypt before decompress, i.e. encrypt after compress, because only the > > plaintext can be compressible; the ciphertext isn't.
WARNING: multiple messages have this Message-ID (diff)
From: hsiangkao@aol.com (Gao Xiang) Subject: [PATCH 10/13] iomap: use a function pointer for dio submits Date: Sat, 10 Aug 2019 07:45:59 +0800 [thread overview] Message-ID: <20190809234554.GA25734@hsiangkao-HP-ZHAN-66-Pro-G1> (raw) In-Reply-To: <20190809204517.GR5482@bombadil.infradead.org> Hi Willy, On Fri, Aug 09, 2019@01:45:17PM -0700, Matthew Wilcox wrote: > On Wed, Aug 07, 2019@10:49:36PM -0700, Eric Biggers wrote: > > On Thu, Aug 08, 2019@12:26:42PM +0800, Gao Xiang wrote: > > > 1. decrypt->verity->decompress > > > > > > 2. verity->decompress->decrypt > > > > > > 3. decompress->decrypt->verity > > > > > > 1. and 2. could cause less computation since it processes > > > compressed data, and the security is good enough since > > > the behavior of decompression algorithm is deterministic. > > > 3 could cause more computation. > > > > > > All I want to say is the post process is so complicated since we have > > > many selection if encryption, decompression, verification are all involved. > > > > > > Maybe introduce a core subset to IOMAP is better for long-term > > > maintainment and better performance. And we should consider it > > > more carefully. > > > > > > > FWIW, the only order that actually makes sense is decrypt->decompress->verity. > > That used to be true, but a paper in 2004 suggested it's not true. > Further work in this space in 2009 based on block ciphers: > https://arxiv.org/pdf/1009.1759 > > It looks like it'd be computationally expensive to do, but feasible. Yes, maybe someone cares where encrypt is at due to their system design. and I thought over these days, I have to repeat my thought of verity again :( the meaningful order ought to be "decrypt->verity->decompress" rather than "decrypt->decompress->verity" if compression is involved. since most (de)compress algorithms are complex enough (allocate memory and do a lot of unsafe stuffes such as wildcopy) and even maybe unsafe by its design, we cannot do verity in the end for security consideration thus the whole system can be vulnerable by this order from malformed on-disk data. In other words, we need to verify on compressed data. Fsverity is fine for me since most decrypt algorithms is stable and reliable and no compression by its design, but if some decrypt software algorithms is complicated enough, I'd suggest "verity->decrypt" as well to some extent. Considering transformation "A->B->C->D->....->verity", if any of "A->B->C ->D->..." is attacked by the malformed on-disk data... It would crash or even root the whole operating system. All in all, we have to verify data earlier in order to get trusted data for later complex transformation chains. The performance benefit I described in my previous email, it seems no need to say again... please take them into consideration and I think it's no easy to get a unique generic post-read order for all real systems. Thanks, Gao Xiang > > > Decrypt before decompress, i.e. encrypt after compress, because only the > > plaintext can be compressible; the ciphertext isn't.
next prev parent reply other threads:[~2019-08-09 23:46 UTC|newest] Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-02 22:00 [PATCH v2 0/13] Btrfs iomap Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 01/13] iomap: Use a IOMAP_COW/srcmap for a read-modify-write I/O Goldwyn Rodrigues 2019-08-03 0:39 ` Darrick J. Wong 2019-08-05 0:06 ` Dave Chinner 2019-08-02 22:00 ` [PATCH 02/13] iomap: Read page from srcmap for IOMAP_COW Goldwyn Rodrigues 2019-08-03 0:23 ` Darrick J. Wong 2019-08-04 23:52 ` Dave Chinner 2019-08-02 22:00 ` [PATCH 03/13] btrfs: Eliminate PagePrivate for btrfs data pages Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 04/13] btrfs: Add a simple buffered iomap write Goldwyn Rodrigues 2019-08-05 0:11 ` Dave Chinner 2019-08-22 15:05 ` Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 05/13] btrfs: Add CoW in iomap based writes Goldwyn Rodrigues 2019-08-05 0:13 ` Dave Chinner 2019-08-22 15:01 ` Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 06/13] btrfs: remove buffered write code made unnecessary Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 07/13] btrfs: basic direct read operation Goldwyn Rodrigues 2019-08-12 12:32 ` RITESH HARJANI 2019-08-22 15:00 ` Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 08/13] btrfs: Carve out btrfs_get_extent_map_write() out of btrfs_get_blocks_write() Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 09/13] btrfs: Rename __endio_write_update_ordered() to btrfs_update_ordered_extent() Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 10/13] iomap: use a function pointer for dio submits Goldwyn Rodrigues 2019-08-03 0:21 ` Darrick J. Wong 2019-08-05 16:08 ` Goldwyn Rodrigues 2019-08-04 23:43 ` Dave Chinner 2019-08-05 16:08 ` Goldwyn Rodrigues 2019-08-05 21:54 ` Dave Chinner 2019-08-08 4:26 ` Gao Xiang 2019-08-08 4:26 ` Gao Xiang 2019-08-08 4:52 ` Gao Xiang 2019-08-08 4:52 ` Gao Xiang 2019-08-08 5:49 ` Eric Biggers 2019-08-08 5:49 ` Eric Biggers 2019-08-08 6:28 ` Gao Xiang 2019-08-08 6:28 ` Gao Xiang 2019-08-08 8:16 ` Dave Chinner 2019-08-08 8:16 ` Dave Chinner 2019-08-08 8:57 ` Gao Xiang 2019-08-08 8:57 ` Gao Xiang 2019-08-08 9:29 ` Gao Xiang 2019-08-08 9:29 ` Gao Xiang 2019-08-08 11:21 ` Gao Xiang 2019-08-08 11:21 ` Gao Xiang 2019-08-08 13:11 ` Gao Xiang 2019-08-08 13:11 ` Gao Xiang 2019-08-09 20:45 ` Matthew Wilcox 2019-08-09 20:45 ` Matthew Wilcox 2019-08-09 23:45 ` Gao Xiang [this message] 2019-08-09 23:45 ` Gao Xiang 2019-08-10 0:31 ` Eric Biggers 2019-08-10 0:31 ` Eric Biggers 2019-08-10 0:50 ` Eric Biggers 2019-08-10 0:50 ` Eric Biggers 2019-08-10 1:34 ` Gao Xiang 2019-08-10 1:34 ` Gao Xiang 2019-08-10 1:13 ` Gao Xiang 2019-08-10 1:13 ` Gao Xiang 2019-08-10 0:17 ` Eric Biggers 2019-08-10 0:17 ` Eric Biggers 2019-08-02 22:00 ` [PATCH 11/13] btrfs: Use iomap_dio_rw for performing direct I/O writes Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 12/13] btrfs: Remove btrfs_dio_data and __btrfs_direct_write Goldwyn Rodrigues 2019-08-02 22:00 ` [PATCH 13/13] btrfs: update inode size during bio completion Goldwyn Rodrigues
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