linux-kernel - Re: [PATCH v2] integrity: track mtime in addition to i

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Date:   Wed, 12 Jul 2017 10:35:04 -0400
From:   Bruce Fields <bfields@...ldses.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     jlayton@...hat.com, Jeff Layton <jlayton@...nel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] integrity: track mtime in addition to i_version for
 assessment

On Wed, Jul 12, 2017 at 08:20:21AM -0400, Mimi Zohar wrote:
> Right, currently the only way of knowing is by looking at the IMA
> measurement list to see if modified files are re-measured or, as you
> said, by looking at the code.

Who's actually using this, and do they do any kind of checks, or
document the filesystem-specific limitations?

--b.

> 
> I started working on adding logging/audit messages, but have not yet
> posted them.  A very preliminary set of patches is available from
> https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.
> git/next-log-iversion-experimental.
> 
> 2745b7be961a ima: indicate possibly missing file measurements or verification
> 0c81a8c56153 security: define new LSM sb_post_new_mount hook
> 
> Mimi
> 
> > 
> > ext4 only provides a working i_version counter when you mount with "-o
> > i_version", so it's trivial to tell there. xfs and btrfs also have
> > functional i_version counter implementations, but there is no such
> > mount option for them (it's always on there). NFSv4 and AFS can provide
> > one too (as they're supplied by the server).
> > 
> > Suppose I want to use IMA on something else (say, ubifs). How do I know
> > whether I'm only going to get "initial file integrity verification and
> > measurement" or whether it'll be updated after being written?
> > 
> > Now, I happen to know that ubifs does _not_ support the i_version
> > counter because I can poke through the kernel sources and tell, but how
> > is Joe Random Linux User to know this?
> > 
> > Does that not matter for some reason? Is there a whitelist of
> > filesystems being maintained in some userland package?
> > 
> > Sorry if it seems like I'm being dense here, but I really just don't
> > understand how we can allow this code to be so cavalier about using the
> > i_version counter without taking steps to ensure that it actually does
> > a damned thing at all.
> 
>