Bug#788062: os-prober corrupts LVs/partitions while being mounted inside a VM

[Chris Kuehl <ckuehl@ocf.berkeley.edu>]

Hi,

If this can't be fixed quickly, would it make sense to push an update
which disables os-prober on jessie in cases which are known to (even
possibly) lead to data loss?

I hate to post a "me too" message, but it's a little disheartening to
know that a bug that causes pretty bad data loss in fairly common
scenarios has been known about since June without being patched in
stable.

We just spent a lot of time and effort pinpointing and recovering from
this bug ourselves. I wish we could help others who are yet to hit this
bug, as surely more people are going to lose data until we patch this.

A simple reproduction:

    - on the host, run
        while :; do os-prober; done
    - on a guest, perform some disk IO, e.g.
        dd if=/dev/zero of=/test

On our systems, this reproduces the issue very quickly. The guest runs
under KVM and the guest's disk is an LVM logical volume. The filesystem
is ext4.

Thanks for your work on Debian!

Chris