From: Eric Biggers <ebiggers@kernel.org>
To: Colin Walters <walters@verbum.org>
Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-integrity@vger.kernel.org, linux-fscrypt@vger.kernel.org,
linux-kernel@vger.kernel.org,
Mimi Zohar <zohar@linux.vnet.ibm.com>,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
Michael Halcrow <mhalcrow@google.com>,
Victor Hsieh <victorhsieh@google.com>
Subject: Re: [RFC PATCH 01/10] fs-verity: add setup code, UAPI, and Kconfig
Date: Fri, 14 Sep 2018 09:21:43 -0700 [thread overview]
Message-ID: <20180914162142.GA734@sol.localdomain> (raw)
In-Reply-To: <1536930930.1003187.1508104496.6465C44D@webmail.messagingengine.com>
Hi Colin,
On Fri, Sep 14, 2018 at 09:15:30AM -0400, Colin Walters wrote:
> On Sat, Aug 25, 2018, at 12:48 AM, Eric Biggers wrote:
> >
> > As Ted pointed out, only truncates are denied on fs-verity files, not other
> > metadata changes like chmod().
> >
> > Think of it this way: the purpose of fs-verity is *not* to make files immutable.
> > It's to hash them.
>
> Sorry for my unfamiliarity with Android internals but - in earlier discussion
> I believe it was mentioned that APK (zip files?) that are being targeted here, right?
>
> Now AIUI, Zip files have an internal header that contains e.g. the size and
> indexes into the internal files. So if someone added random data to the end
> of a zip file, nothing is going to end up actually reading it.
>
> However, there are file formats that use the size of the file reported by stat();
> at least OSTree does this with serializing GVariant. I'm sure there are others -
> I'd imagine at least some things parsing ELF do this?
> In such a case, we really want to deny appending to the file as well.
>
> Unless there's some mechanism to deny applications reading not-verified
> data?
>
> And "hidden" data after fs-verity protected files would be a nice place
> for persistent malware to hide.
>
> Does anyone know of a use case for appending to a fs-verity file?
>
> The slides here:
> https://events.linuxfoundation.org/wp-content/uploads/2017/11/fs-verify_Mike-Halcrow_Eric-Biggers.pdf
> even say "File becomes read-only!"
>
> If not, then here's a strawman: Require that at FS_IOC_ENABLE_VERITY time
> the file does not have any +w bits set (and I guess no ACLs that do so...
> that may get ugly).
>
> I think that would make it easier to later factor out a "_CONTENTS_IMMUTABLE"
> flag.
>
After the verity bit is enabled, the verity metadata is not visible to
userspace. Yes, that means i_size is adjusted too. Also all contents
modifications are denied, including appends.
- Eric
next prev parent reply other threads:[~2018-09-14 21:36 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 [this message]
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
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
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