[Libguestfs] [PATCH nbdkit] vddk: Disallow password=-

[Richard W.M. Jones]

On Mon, Jun 01, 2020 at 12:13:13PM -0500, Eric Blake wrote:
> On 6/1/20 11:07 AM, Richard W.M. Jones wrote:
> >This has been broken since we added the reexec code
> >(commit 155af3107292c351d54ed42c732f4a67bb9aa910) because it
> >tried to read the password twice (before and after the reexec) failing
> >the second time because stdin had already been reopened on /dev/null.
> >
> >Virt-v2v used this feature, but I will change virt-v2v instead.
> >---
> >  plugins/vddk/nbdkit-vddk-plugin.pod | 7 +------
> >  plugins/vddk/vddk.c                 | 4 ++++
> >  2 files changed, 5 insertions(+), 6 deletions(-)
> 
> This is the simplest "fix", by avoiding the problem. It may still be
> possible to come up with something more robust, where (since we are
> already special-casing for "-" as the password value) we read the
> password prior to re-exec, and rewrite the command line of the
> re-exec to instead consume a temporary file.  But that's more
> complex, and doesn't stop us from pushing this now; if we ever do
> implement the more complex patch, we can roll back the documentation
> change.
> 
> And I already see that you have the counterpart v2v patch that
> hoists the reading of the password into v2v instead of worrying
> about vddk; the v2v hack of using a temporary file "works" in spite
> of our re-exec reading it twice, even if we want to eventually reach
> the point where a more complex patch in the vddk plugin would only
> read the password once before re-exec.

The other advantage with doing this in virt-v2v is that there is a
place to clean up this temporary file.  There was as far as I could
tell no easy way for nbdkit to reexec itself with
password=+/tmp/<generated file> and have that file get cleaned up.
Not a problem since the file is not large, but nicer not to leave
passwords around if we can help it.

Thanks,

Rich.

> ACK.
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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