[Libguestfs] qemu command line quoting (was: Re: [PATCH 0/5] rbd improvements)

Richard W.M. Jones rjones at redhat.com
Sun May 12 20:15:33 UTC 2013

On Sun, May 12, 2013 at 02:42:36PM -0400, Mike Kelly wrote:
> On Thu, May 9, 2013 at 12:21 PM, Richard W.M. Jones <rjones at redhat.com> wrote:
> > On Thu, May 09, 2013 at 11:23:55AM -0400, Mike Kelly wrote:
> >> On Wed, May 8, 2013 at 6:53 AM, Richard W.M. Jones <rjones at redhat.com> wrote:
> >> > One worry I have is whether quoting is required for the server
> >> > name(s), export name, username and secret.
> >>
> >> Well. I think the main things we had to quote were ':' and ';', but
> >> none of those are valid in a hostname. Username also probably doesn't
> >> contain anything special, and secret is a base64-encoded string. I
> >> confirmed that even with the string ending in '==', it was parsed just
> >> fine by qemu, at least in my limited manual testing.
> >>
> >> If you can suggest a way to be more robust this, though, then I can
> >> try to work that into a future patch series.
> >
> > The quoting problem happens when someone writes a program which takes
> > (eg) a hostname string from the user and passes it unmodified to the
> > guestfs API.  It's an issue if this string can cause unexpected [even
> > malicious/exploitable] things to happen when passed unquoted on the
> > qemu command line.
> Well, I'm not sure if this way of setting things up is still
> encouraged, but at least this documentation suggests basically using
> the fact that libvirt won't quote the image name as a "feature":
>   http://ceph.com/w/index.php?title=QEMU-RBD#Caching
>    <disk type='network' device='disk'>
>       <source protocol='rbd'
> name='poolname/imagename:rbd_cache=1:rbd_cache_size=67108864:rbd_cache_max_dirty=0'/>

Hmmm ...  This is a bug in libvirt, but also a missing feature of
libvirt since it cannot express these other configuration fields.

>       <driver name='qemu' type='rbd'/>
>       <target dev='vda' bus='virtio'/>
>     </disk>
> The more official documentation for configuring caching doesn't seem
> to make any specific mention of this:
>   http://ceph.com/docs/master/rbd/qemu-rbd/#qemu-cache-options
>   http://ceph.com/docs/master/rbd/libvirt/
>   http://ceph.com/docs/master/rbd/rbd-config-ref/

By the way, I fixed some qemu-img command line quoting issues
yesterday (but not in ceph):



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