[cap-talk] MinorFs: delegation now works

[Toby Murray]

Hi Rob

I find this work interesting and would encourage you to periodically
post on your progress and ideas regarding how it could be best applied
in practice.

Cheers

Toby

On Fri, 2008-02-01 at 17:15 +0100, Rob Meijer wrote:
> First let me start of by asking if there is anyone here besides me who
> thinks me posting my progress on MinorFs is relevant? I didn't get any
> replies on my previous progress post, so possibly I'm working on an area
> that is of very low interest to people on this list.
> If this is the case I'll stop posting them.
> 
> I've just bundled a new alpha version of MinorFs.
> 
> http://polacanthus.net/minorfs-0.0.2.tar.gz
> 
> MinorFs is a set of simple fuse userspace filesystems for Linux aimed
> to be learning tools for practical POLA/POPL usage in a Linux environment.
> The main result of this learning tool focus is that performance has not
> been a design or implementation focus.
> 
> Where the previous version only implemented private storage for pseudo
> persistent processes, the new version now allows these processes to take
> a file or directory from its private directory tree, request a password
> capability path from this file or directory (by requesting the
> 'delegatable' extended attribute). This capability path than can be
> communicated with any
> other process using paths of communication (these paths of communication
> are not provided by the file system, but are in my view over sufficiently
> available in the Linux environment).
> 
> I'll past the README of the project below
> 
> Rob
> ----------------------------------------------------------------------
> MinorFs is a set of simple user space filesystems that work together to
> provide the folowing functionality:
> 
> * Nth claim persistent processes (minorviewfs)
> * Persisten private storage      (minorviewfs)
> * Delegation                     (minorcapfs)
> 
> Future versions shall also include:
> * Revocation                     (minorcaretakerfs)
> * Attenuation                    (minorcaretakerfs)
> 
> 
> This readme gives a short explanation of how the seperate filesystems
> work and how they work together.
> 
> MinorViewFs creates a private directory for processes. Given that processes
> and their base identification (pids) are non persistent, and storage is
> persistent, the MinorViewFs filesystem allows processes the possibility to
> 'claim' an unused slot that was previously used by a process that was an
> instance of the same executable running under the same user id as the current
> process.
> This claiming of a slot turns the process into an incarnation of some
> 'persistent' process, allowing it to make use of the 'private' directory
> to store its state.
> 
> MinorFs allows most operations that a normal filesystem allows, but there
> are some differences. Links and symlinks are not supported, and chmod
> operations
> don't have any effect given that they are useless with respect to the
> security model that minorviewfs provides.
> 
> Please note that minorviewfs does not work well together with scripts, as
> the data will become private to the interpreter rather than to the script.
> Further note that currently persistent storage is limited to 32 concurent
> versions of the same program running with the same uid.
> 
> An important operation that MinorViewfs provides that makes it work together
> well with MinorCapFs is the use of a special extended attribute.
> The extended attribute 'delegatable' that is made available for each file
> and directory, returns a path to the same underlaying directory but than
> through MinorCapFs. In contrast to the MinorViewFs paths, the paths into
> MinorCapFs can be delegated to other processes, even to other users.
> The MinorCapFs paths contain a token that is in fact a very basic
> implemetation of a so called 'password capability'.
> 
> 
> Attenuation and revocations are not yet addressed in this version
> of minorfs.
> The upcomming version of minorfs will aim to also provide additional minor
> filesystems for these purposes.
> 
> New versions will be available shortly on: http://polacanthus.net/
> 
> If you run into any bugs or problems, I will be very gratefull if you could
> report them to : minorfs at polacanthus.net
> 
> 
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