[libvirt] [PATCH 3/8] storage: Prior to creating a volume, refresh the pool

[Ján Tomko]

On Mon, Oct 05, 2015 at 07:27:34PM -0400, John Ferlan wrote:
> 
> 
> On 10/05/2015 07:28 AM, Michal Privoznik wrote:
> > On 02.10.2015 15:41, John Ferlan wrote:
> >> https://bugzilla.redhat.com/show_bug.cgi?id=1233003
> >>
> >> Although perhaps bordering on a don't do that type scenario, if
> >> someone creates a volume in a pool outside of libvirt, then uses that
> >> same name to create a volume in the pool via libvirt, then the creation
> >> will fail and in some cases cause the same name volume to be deleted.
> >>
> >> This patch will refresh the pool just prior to checking whether the
> >> named volume exists prior to creating the volume in the pool. While
> >> it's still possible to have a timing window to create a file after the
> >> check - at least we tried.  At that point, someone is being malicious.
> >>
> >> Signed-off-by: John Ferlan <jferlan at redhat.com>
> >> ---
> >>  src/storage/storage_driver.c | 9 +++++++++
> >>  1 file changed, 9 insertions(+)
> >>
> >> diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
> >> index 7aaa060..ddf4405 100644
> >> --- a/src/storage/storage_driver.c
> >> +++ b/src/storage/storage_driver.c
> >> @@ -1796,6 +1796,15 @@ storageVolCreateXML(virStoragePoolPtr obj,
> >>      if (virStorageVolCreateXMLEnsureACL(obj->conn, pool->def, voldef) < 0)
> >>          goto cleanup;
> >>  
> >> +    /* While not perfect, refresh the list of volumes in the pool and
> >> +     * then check that the incoming name isn't already in the pool.
> >> +     */
> >> +    if (backend->refreshPool) {
> >> +        virStoragePoolObjClearVols(pool);
> >> +        if (backend->refreshPool(obj->conn, pool) < 0)
> >> +            goto cleanup;
> >> +    }
> >> +
> >>      if (virStorageVolDefFindByName(pool, voldef->name)) {
> >>          virReportError(VIR_ERR_STORAGE_VOL_EXIST,
> >>                         _("'%s'"), voldef->name);
> >>
> >

This is a workaround for the linked bug, not a fix. Refreshing the pool
seems excessive to me.

> > Okay, this makes sense. Not only from the POV you are presenting, but I'd expect my pool to be refreshed after I create new volume in it.
> > 

Other volume APIs don't refresh the pool, I think we should be
consistent.

> > And I think we have a way to eliminate even the little window - just track if we successfully built the volume or not. Something among these lines:
> > 

After properly propagating the error value if the volume exists, we
don't need this patch refreshing the pool to work around the original
bug.

Jan
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