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[Qemu-devel] Re: [RFC][PATCH v5 08/21] virtagent: add agent_viewfile qmp

From: Jes Sorensen
Subject: [Qemu-devel] Re: [RFC][PATCH v5 08/21] virtagent: add agent_viewfile qmp/hmp command
Date: Mon, 13 Dec 2010 09:29:27 +0100
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On 12/10/10 18:09, Michael Roth wrote:
> I think with strictly enforced size limits the major liability for
> viewfile is, as you mentioned, users using it to view binary data or
> carefully crafted files that can mess up or fool users/shells/programs
> interpreting monitor output.
> But plain-text does not include escape sequences, so it's completely
> reasonable that we'd scrape them. And I'm not sure if a "(qemu)" in the
> text is a potential liability. Would there be any other issues to consider?
> If we can guard against those things, do you agree it wouldn't be an
> inherently dangerous interface? State-full, asynchronous RPCs like
> copyfile and exec are not really something I'd planned for the initial
> release. I think they'll take some time to get right, and a simple
> low-risk interface to cover what I'm fairly sure is the most common use
> case seems reasonable.

I am still wary of relying on strict limit enforcement. It is the sort
of thing that will eventually change without us noticing and we end up
with a security hole.

IMHO QEMU should not try to do these sorts of things, instead it should
provide the transport and control services. I don't think file viewing
belongs in QEMU at all. I would be a lot more comfortable if this was
implemented as a standalone monitor interface that connected to QEMU's
QMP interface. I could then use QMP to perform actions like copying the
file to /tmp and if viewing the file caused the monitor to lock up, we
wouldn't lose the guest. This could indeed be the start of an external
monitor :)


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