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From: James Morris <jmorris@namei.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>,
	linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, Miklos Szeredi <miklos@szeredi.hu>,
	Seth Forshee <seth.forshee@canonical.com>,
	Dongsu Park <dongsu@kinvolk.io>, Alban Crequy <alban@kinvolk.io>,
	"Serge E . Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH v1 1/2] ima: fail signature verification on untrusted filesystems
Date: Tue, 20 Feb 2018 11:52:42 +1100 (AEDT)	[thread overview]
Message-ID: <alpine.LRH.2.21.1802201152240.883@namei.org> (raw)
In-Reply-To: <87zi44mz26.fsf@xmission.com>

On Mon, 19 Feb 2018, Eric W. Biederman wrote:

> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> 
> > Files on untrusted filesystems, such as fuse, can change at any time,
> > making the measurement(s) and by extension signature verification
> > meaningless.
> 
> Filesystems with servers?
> Remote filesystems?
> Perhaps unexpected changes.
> 
> Untrusted sounds a bit harsh, and I am not certain it quite captures
> what you are looking to avoid.

Right -- I think whether you trust a filesystem or not depends on how much 
assurance you have in your specific configuration, rather than whether you 
think the filesystem can be manipulated or not.

There is a difference between:

  - This fs has no way to communicate a change to IMA, and;

  - This fs could be malicious.

In the latter case, I suggest that any fs could be malicious if the 
overall security policy / settings are inadequate for the threat model, or 
if there are vulnerabilities which allow such security to be bypassed.

Whether a user trusts FUSE on their particular system should be a policy 
decision on the part of the user.  The kernel should not be deciding what 
is trusted or not trusted here.



-- 
James Morris
<jmorris@namei.org>

WARNING: multiple messages have this Message-ID (diff)
From: jmorris@namei.org (James Morris)
To: linux-security-module@vger.kernel.org
Subject: [PATCH v1 1/2] ima: fail signature verification on untrusted filesystems
Date: Tue, 20 Feb 2018 11:52:42 +1100 (AEDT)	[thread overview]
Message-ID: <alpine.LRH.2.21.1802201152240.883@namei.org> (raw)
In-Reply-To: <87zi44mz26.fsf@xmission.com>

On Mon, 19 Feb 2018, Eric W. Biederman wrote:

> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> 
> > Files on untrusted filesystems, such as fuse, can change at any time,
> > making the measurement(s) and by extension signature verification
> > meaningless.
> 
> Filesystems with servers?
> Remote filesystems?
> Perhaps unexpected changes.
> 
> Untrusted sounds a bit harsh, and I am not certain it quite captures
> what you are looking to avoid.

Right -- I think whether you trust a filesystem or not depends on how much 
assurance you have in your specific configuration, rather than whether you 
think the filesystem can be manipulated or not.

There is a difference between:

  - This fs has no way to communicate a change to IMA, and;

  - This fs could be malicious.

In the latter case, I suggest that any fs could be malicious if the 
overall security policy / settings are inadequate for the threat model, or 
if there are vulnerabilities which allow such security to be bypassed.

Whether a user trusts FUSE on their particular system should be a policy 
decision on the part of the user.  The kernel should not be deciding what 
is trusted or not trusted here.



-- 
James Morris
<jmorris@namei.org>

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  reply	other threads:[~2018-02-20  1:56 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-19 15:18 [PATCH v1 0/2] ima: untrusted filesystems Mimi Zohar
2018-02-19 15:18 ` Mimi Zohar
2018-02-19 15:18 ` [PATCH v1 1/2] ima: fail signature verification on " Mimi Zohar
2018-02-19 15:18   ` Mimi Zohar
2018-02-19 21:47   ` Eric W. Biederman
2018-02-19 21:47     ` Eric W. Biederman
2018-02-20  0:52     ` James Morris [this message]
2018-02-20  0:52       ` James Morris
2018-02-20  2:02       ` Eric W. Biederman
2018-02-20  2:02         ` Eric W. Biederman
2018-02-20 14:02         ` Mimi Zohar
2018-02-20 14:02           ` Mimi Zohar
2018-02-20 14:02           ` Mimi Zohar
2018-02-20 20:16           ` Serge E. Hallyn
2018-02-20 20:16             ` Serge E. Hallyn
2018-02-20 20:16             ` Serge E. Hallyn
2018-02-21 14:46             ` Mimi Zohar
2018-02-21 14:46               ` Mimi Zohar
2018-02-21 14:46               ` Mimi Zohar
2018-02-21 22:46               ` Eric W. Biederman
2018-02-21 22:46                 ` Eric W. Biederman
2018-02-21 22:46                 ` Eric W. Biederman
2018-02-21 22:57                 ` Mimi Zohar
2018-02-21 22:57                   ` Mimi Zohar
2018-02-21 22:57                   ` Mimi Zohar
2018-02-21 23:12                   ` Eric W. Biederman
2018-02-21 23:12                     ` Eric W. Biederman
2018-02-21 23:12                     ` Eric W. Biederman
2018-02-21 23:32                     ` Mimi Zohar
2018-02-21 23:32                       ` Mimi Zohar
2018-02-21 23:32                       ` Mimi Zohar
2018-02-27  2:12                       ` Eric W. Biederman
2018-02-27  2:12                         ` Eric W. Biederman
2018-02-27  2:12                         ` Eric W. Biederman
2018-02-21 22:53           ` Eric W. Biederman
2018-02-21 22:53             ` Eric W. Biederman
2018-02-21 22:53             ` Eric W. Biederman
2018-02-21 23:03             ` Mimi Zohar
2018-02-21 23:03               ` Mimi Zohar
2018-02-21 23:03               ` Mimi Zohar
2018-02-19 22:50   ` kbuild test robot
2018-02-19 22:50     ` kbuild test robot
2018-02-19 22:50     ` kbuild test robot
2018-02-19 23:36   ` kbuild test robot
2018-02-19 23:36     ` kbuild test robot
2018-02-19 23:36     ` kbuild test robot
2018-02-19 15:18 ` [PATCH v1 2/2] fuse: define the filesystem as untrusted Mimi Zohar
2018-02-19 15:18   ` Mimi Zohar

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