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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

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