linux-kernel - Re: [PATCH 0/2] turn on force option for FUSE in builtin policies

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Date:   Mon, 15 Jan 2018 16:00:23 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dongsu Park <dongsu@...volk.io>, linux-kernel@...r.kernel.org,
        Alban Crequy <alban@...volk.io>,
        Miklos Szeredi <miklos@...redi.hu>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-integrity <linux-integrity@...r.kernel.org>
Subject: Re: [PATCH 0/2] turn on force option for FUSE in builtin policies

On Mon, 2018-01-15 at 09:18 -0800, Christoph Hellwig wrote:
> On Mon, Jan 15, 2018 at 11:32:41AM -0500, Mimi Zohar wrote:
> > For XFS, which considers fsmagic numbers private to the filesystem,
> > *always* using the fsmagic number is wrong.  As to whether this is
> > true for other filesystems is unclear.  IMA policies have been defined
> > in terms of fsmagic numbers for a long time.  fsmagic numbers were
> > moved from the filesystems to magic.h for this purpose.  Someone would
> > have complained earlier if it is always wrong.
> >  
> > I just posted a patch titled "ima: define new policy condition based
> > on the filesystem name" to allow policies to be defined in terms of
> > the i_sb->s_type->name.
> 
> ima has no business looking at either the name _or_ the magic number.

There are a couple of reasons to define policies in terms of the
filesystem name or magic numbers.

One example is pseudo filesystems (eg. pseudo filesystems - sysfs,
securitys, cgroups, selinuxfs, etc).  These should never be measured
or appraised.

The current example is fuse and remote file systems.  These should
always be re-evaluated and not rely on cached file info.

If not based on IMA policy, what do you propose?  Define new SB_ flags
 to indicate IMA disabled/enabled (eg. SB_IMA) and nocaching (eg.
SB_IMA_NOCACHE)?

Mimi