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Re: [Qemu-devel] [PATCH] ps2: fix PS2Queue counter field type

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] [PATCH] ps2: fix PS2Queue counter field type
Date: Wed, 15 Nov 2017 13:30:35 +0000
User-agent: Mutt/1.9.1 (2017-09-22)

* Paolo Bonzini (address@hidden) wrote:
> On 15/11/2017 13:51, Daniel P. Berrange wrote:
> > If you're concerned that someone is tampering with QEMU state
> > in transit during migration, then you're going to end up playing
> > whack-a-mole across the entire QEMU codebase IMHO. The answer
> > to the problem of tampering is to have encryption of the
> > migration data stream between both QEMU's. Thus QEMU on the
> > target merely has to trust QEMU on the source. If QEMU on the
> > source is itself compromised you've already lost and migration
> > won't make life any worse.
> > 
> This is not entirely true.  A lot of such cases were fixed in the past,
> especially when they could cause out-of-bounds access.  Someone could
> provide a bad migration stream (e.g. as a fake bug report!), so
> migration data should not be considered trusted.

There's probably others to be honest; it's not something we've
traditionally been careful of.

> However, PJP's patch breaks migration by changing a 4-byte field to
> 1-byte.  The correct fix is to range-check the fields in
> ps2_common_post_load.



> Thanks,
> Paolo
Dr. David Alan Gilbert / address@hidden / Manchester, UK

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