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From: Matthew Garrett <mjg59@google.com>
To: zohar@linux.ibm.com
Cc: linux-integrity <linux-integrity@vger.kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	miklos@szeredi.hu, linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: Allow FUSE filesystems to provide out-of-band hashes to IMA
Date: Fri, 5 Oct 2018 10:26:51 -0700	[thread overview]
Message-ID: <CACdnJusoTGYAZgK3eTEew=HtUpuY4ra_6eQyGa4WWxjZPagXjQ@mail.gmail.com> (raw)
In-Reply-To: <1538736566.3702.436.camel@linux.ibm.com>

On Fri, Oct 5, 2018 at 3:49 AM Mimi Zohar <zohar@linux.ibm.com> wrote:

> Really, a security vs. performance argument?!  I don't need to tell
> you of all people, that one of the basic tenents of trusted boot is
> calculating the actual file hash before use.  Limiting the file hash
> re-calculation is one thing, but relying on some out of band method of
> obtaining the file hash without the kernel ever calculating it is
> totally different.  The only exception will be for fs-verity, which
> will return not the file hash, but the file's Merkle tree root hash.

Using FUSE means you're inherently accepting the risk of TOCTOU.
Having the kernel read everything once and hash it is no guarantee
that the filesystem will return the same value on further reads, so if
you're going to use FUSE in an environment where you're using IMA then
you already need to assert that your filesystems are trustworthy.

  reply	other threads:[~2018-10-06  0:26 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-04 20:30 Allow FUSE filesystems to provide out-of-band hashes to IMA Matthew Garrett
2018-10-04 20:30 ` [PATCH 1/3] VFS: Add a call to obtain a file's hash Matthew Garrett
2018-10-11 15:22   ` Mimi Zohar
2018-10-11 15:22     ` Mimi Zohar
2018-10-11 18:21     ` Matthew Garrett
2018-10-11 18:24       ` Matthew Garrett
2018-10-11 18:37         ` Mimi Zohar
2018-10-11 18:37           ` Mimi Zohar
2018-10-11 18:43           ` Matthew Garrett
2018-10-04 20:30 ` [PATCH 2/3] IMA: Make use of filesystem-provided hashes Matthew Garrett
2018-10-11 15:23   ` Mimi Zohar
2018-10-11 15:23     ` Mimi Zohar
2018-10-11 20:30     ` Matthew Garrett
2018-10-11 23:03       ` Mimi Zohar
2018-10-12 18:31         ` Matthew Garrett
2018-10-15  1:38           ` Mimi Zohar
2018-10-15  1:38             ` Mimi Zohar
2018-10-15 18:46             ` Matthew Garrett
2018-10-16 13:16               ` Mimi Zohar
2018-10-16 13:16                 ` Mimi Zohar
2018-10-04 20:30 ` [PATCH 3/3] FUSE: Allow filesystems to provide gethash methods Matthew Garrett
2018-10-05 10:49 ` Allow FUSE filesystems to provide out-of-band hashes to IMA Mimi Zohar
2018-10-05 10:49   ` Mimi Zohar
2018-10-05 17:26   ` Matthew Garrett [this message]
2018-10-05 18:18     ` Mimi Zohar
2018-10-05 19:25       ` Matthew Garrett
2018-10-08 11:25         ` Mimi Zohar
2018-10-08 11:25           ` Mimi Zohar
2018-10-08 20:19           ` Matthew Garrett
2018-10-08 22:40             ` Mimi Zohar
2018-10-08 22:40               ` Mimi Zohar
2018-10-09 17:21               ` Matthew Garrett
2018-10-09 18:04                 ` Mimi Zohar
2018-10-09 19:29                   ` Matthew Garrett
2018-10-09 20:52                     ` Mimi Zohar
2018-10-09 21:32                       ` Matthew Garrett
2018-10-10 11:09                         ` Mimi Zohar
2018-10-10 11:09                           ` Mimi Zohar
2018-10-10 16:19                           ` Matthew Garrett

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