From: Olof Johansson <olof@lixom.net>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Gao Xiang <gaoxiang25@huawei.com>,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
Michael Halcrow <mhalcrow@google.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fscrypt@vger.kernel.org, linux-integrity@vger.kernel.org,
Mimi Zohar <zohar@linux.vnet.ibm.com>,
Victor Hsieh <victorhsieh@google.com>
Subject: Re: [RFC PATCH 02/10] fs-verity: add data verification hooks for ->readpages()
Date: Sat, 1 Sep 2018 19:35:53 -0700 [thread overview]
Message-ID: <CAOesGMhGfesVQHHMpqW5r7gMOZccX4RsZZex6y-kfkmuA6K0ow@mail.gmail.com> (raw)
In-Reply-To: <20180825041647.GA726@sol.localdomain>
Hi,
On Fri, Aug 24, 2018 at 9:16 PM, Eric Biggers <ebiggers@kernel.org> wrote:
> Hi Gao,
>
> On Sat, Aug 25, 2018 at 10:29:26AM +0800, Gao Xiang wrote:
>> Hi,
>>
>> At last, I hope filesystems could select the on-disk position of hash tree and 'struct fsverity_descriptor'
>> rather than fixed in the end of verity files...I think if fs-verity preparing such support and interfaces could be better.....hmmm... :(
>
> In theory it would be a much cleaner design to store verity metadata separately
> from the data. But the Merkle tree can be very large. For example, a 1 GB file
> using SHA-512 would have a 16.6 MB Merkle tree. So the Merkle tree can't be an
> extended attribute, since the xattrs API requires xattrs to be small (<= 64 KB),
> and most filesystems further limit xattr sizes in their on-disk format to as
> little as 4 KB. Furthermore, even if both of these limits were to be increased,
> the xattrs functions (both the syscalls, and the internal functions that
> filesystems have) are all based around getting/setting the entire xattr value.
>
> Also when used with fscrypt, we want the Merkle tree and fsverity_descriptor to
> be encrypted, so they doesn't leak plaintext hashes. And we want the Merkle
> tree to be paged into memory, just like the file contents, to take advantage of
> the usual Linux memory management.
>
> What we really need is *streams*, like NTFS has. But the filesystems we're
> targetting don't support streams, nor does the Linux syscall interface have any
> API for accessing streams, nor does the VFS support them.
>
> Adding streams support to all those things would be a huge multi-year effort,
> controversial, and almost certainly not worth it just for fs-verity.
>
> So simply storing the verity metadata past i_size seems like the best solution
> for now.
>
> That being said, in the future we could pretty easily swap out the calls to
> read_mapping_page() with something else if a particular filesystem wanted to
> store the metadata somewhere else. We actually even originally had a function
> ->read_metadata_page() in the filesystem's fsverity_operations, but it turned
> out to be unnecessary and I replaced it with directly calling
> read_mapping_page(), but it could be changed back at any time.
What about an xattr not to hold the Merkle tree, but to contain a
suitable reference to a file/inode+offset that contains it (+ toplevel
hash for said tree/file or the descriptor/struct)?
If you also expose said file in the directory structure, things such
as backups might be easier to handle. For where the tree is appended
to the file, you could self-reference.
-Olof
next prev parent reply other threads:[~2018-09-02 2:36 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-24 16:16 [RFC PATCH 00/10] fs-verity: filesystem-level integrity protection Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 01/10] fs-verity: add setup code, UAPI, and Kconfig Eric Biggers
2018-08-24 17:28 ` Randy Dunlap
2018-08-24 17:42 ` Colin Walters
2018-08-24 22:45 ` Theodore Y. Ts'o
2018-08-25 4:48 ` Eric Biggers
2018-09-14 13:15 ` Colin Walters
2018-09-14 16:21 ` Eric Biggers
2018-09-15 15:27 ` Theodore Y. Ts'o
2018-08-26 16:22 ` Chuck Lever
2018-08-26 17:17 ` Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 02/10] fs-verity: add data verification hooks for ->readpages() Eric Biggers
2018-08-25 2:29 ` [f2fs-dev] " Gao Xiang
2018-08-25 3:45 ` Theodore Y. Ts'o
2018-08-25 4:00 ` Gao Xiang
2018-08-25 5:06 ` Theodore Y. Ts'o
2018-08-25 7:33 ` Gao Xiang
2018-08-25 7:55 ` Gao Xiang
2018-08-25 4:16 ` Eric Biggers
2018-08-25 6:31 ` Gao Xiang
2018-08-25 7:18 ` Eric Biggers
2018-08-25 7:43 ` Gao Xiang
2018-08-25 17:06 ` Theodore Y. Ts'o
2018-08-26 13:44 ` Gao Xiang
2018-09-02 2:35 ` Olof Johansson [this message]
2018-08-26 15:55 ` Chuck Lever
2018-08-26 17:04 ` Eric Biggers
2018-08-26 17:44 ` Gao Xiang
2018-08-24 16:16 ` [RFC PATCH 03/10] fs-verity: implement FS_IOC_ENABLE_VERITY ioctl Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 04/10] fs-verity: implement FS_IOC_MEASURE_VERITY ioctl Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 05/10] fs-verity: add SHA-512 support Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 06/10] fs-verity: add CRC-32C support Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 07/10] fs-verity: support builtin file signatures Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 08/10] ext4: add basic fs-verity support Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 09/10] ext4: add fs-verity read support Eric Biggers
2018-08-24 16:16 ` [RFC PATCH 10/10] f2fs: fs-verity support Eric Biggers
2018-08-25 5:54 ` [f2fs-dev] " Chao Yu
2018-08-26 17:35 ` Eric Biggers
2018-08-27 15:54 ` Chao Yu
2018-08-28 7:27 ` Jaegeuk Kim
2018-08-28 9:20 ` Chao Yu
2018-08-28 17:01 ` Jaegeuk Kim
2018-08-29 1:22 ` Chao Yu
2018-08-29 1:43 ` Jaegeuk Kim
2018-08-31 20:05 ` [RFC PATCH 00/10] fs-verity: filesystem-level integrity protection Jan Lübbe
2018-08-31 21:39 ` Eric Biggers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAOesGMhGfesVQHHMpqW5r7gMOZccX4RsZZex6y-kfkmuA6K0ow@mail.gmail.com \
--to=olof@lixom.net \
--cc=dmitry.kasatkin@gmail.com \
--cc=ebiggers@kernel.org \
--cc=gaoxiang25@huawei.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-f2fs-devel@lists.sourceforge.net \
--cc=linux-fscrypt@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mhalcrow@google.com \
--cc=victorhsieh@google.com \
--cc=zohar@linux.vnet.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).