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xen-devel
Re: [Xen-devel] [PATCH 0/3] domUloader
Kurt Garloff wrote:
Hi Anthony,
I knew there was some security concerns voiced about this many
months ago. I think one of the advantages to using libext2 was that it
theoritically allowed the filesystem parsing to be done as a
non-privileged user.
I can see your point.
There's two concerns you could have:
1. When the domU fs gets mounted in dom0, a local user there could
get (read-only) access to data that he shouldn't have access to.
This can be prevented by mounting under a directory that's not
readable to anyone but root. I didn't do this in my patch set,
but it's certainly a good idea.
(And dom0 root you need to trust anyway, such is the trust model
in a hybrid virtualization model without encrypting everything.)
2. The filesystem in the domU could be prepared such that the kernel
trips over a bug in its filesystem code.
The same can happen if you read the FS with a userspace library
of course, but the effects would be less bad -- at least if you
would do it with non-root euid.
The downside is that need to use a secondary source for filesystem
code, which needs to be maintained and kept in sync, audited, ...
And you are limited to the filesystems where you have userspace
libraries for.
In a paranoid scenario, you would not load any data from the domU
filesystem in any way :-) But I can see why you would choose
pygrub over domUloader in a sensitive environment, where you
can't trust the domU admins. Point taken.
I still think that in many use scenarios, you would be perfectly
fine with domUloader.
Did I catch your concerns?
Yup, just wanted to make sure it was considered :-)
Regards,
Anthony Liguori
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