[Xen-devel] RE: [RFC] transcendent memory for Linux

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx]
> On 06/29/09 14:57, Dan Magenheimer wrote:
> > Interesting question.  But, more than the 128-bit UUID must
> > be guessed... a valid 64-bit object id and a valid 32-bit
> > page index must also be guessed (though most instances of
> > the page index are small numbers so easy to guess).  Once
> > 192 bits are guessed though, yes, the pages could be viewed
> > and modified.  I suspect there are much more easily targeted
> > security holes in most data centers than guessing 192 (or
> > even 128) bits.
> 
> If its possible to verify the uuid is valid before trying to find a
> valid oid+page, then its much easier (since you can concentrate on the
> uuid first).

No, the uuid can't be verified.  Tmem gives no indication
as to whether a newly-created pool is already in use (shared)
by another guest.  So without both the 128-bit uuid and an
already-in-use 64-bit object id and 32-bit page index, no data
is readable or writable by the attacker.

> You also have to consider the case of a domain which was once part of
> the ocfs cluster, but now is not - it may still know the uuid, but not
> be otherwise allowed to use the cluster.
> If the uuid is derived from something like the
> filesystem's uuid - which wouldn't normally be considered sensitive
> information - then its not like its a search of the full 
> 128-bit space. 
> And even if it were secret, uuids are not generally 128 
> randomly chosen bits.

Hmmm... that is definitely a thornier problem.  I guess the
security angle definitely deserves more design.  But, again,
this affects only shared precache which is not intended
to part of the proposed initial tmem patchset, so this is a futures
issue.)

Thanks again for the feedback!
Dan

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