[libvirt] [PATCH 1/4] virt-aa-helper: fix paths for usb hostdevs

[Christian Ehrhardt]

On Fri, Sep 29, 2017 at 4:58 PM, Michal Privoznik <mprivozn at redhat.com>
wrote:

> On 09/20/2017 04:59 PM, Christian Ehrhardt wrote:
> > If users only specified vendor&product (the common case) then parsing
> > the xml via virDomainHostdevSubsysUSBDefParseXML would only set these.
> > Bus and Device would much later be added when the devices are prepared
> > to be added.
> >
> > Due to that a hot-add of a usb hostdev works as the device is prepared
> > and virt-aa-helper processes the new internal xml. But on an initial
> > guest start at the time virt-aa-helper renders the apparmor rules the
> > bus/device id's are not set yet:
> >
> > p ctl->def->hostdevs[0]->source.subsys.u.usb
> > $12 = {autoAddress = false, bus = 0, device = 0, vendor = 1921, product
> > = 21888}
> >
> > That causes rules to be wrong:
> >   "/dev/bus/usb/000/000" rw,
> >
> > The fix calls virHostdevFindUSBDevice after reading the XML from
> > irt-aa-helper to only add apparmor rules for devices that could be found
> > and now are fully known to be able to write the rule correctly.
> >
> > It uncondtionally sets virHostdevFindUSBDevice mandatory attribute as
> > adding an apparmor rule for a device not found makes no sense no matter
> > what startup policy it has set.
> >
> > Signed-off-by: Christian Ehrhardt <christian.ehrhardt at canonical.com>
> > ---
> >  src/security/virt-aa-helper.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/src/security/virt-aa-helper.c
> b/src/security/virt-aa-helper.c
> > index 7944dc1..d1518ea 100644
> > --- a/src/security/virt-aa-helper.c
> > +++ b/src/security/virt-aa-helper.c
> > @@ -55,6 +55,7 @@
> >  #include "virrandom.h"
> >  #include "virstring.h"
> >  #include "virgettext.h"
> > +#include "virhostdev.h"
> >
> >  #include "storage/storage_source.h"
> >
> > @@ -1069,6 +1070,9 @@ get_files(vahControl * ctl)
> >                  if (usb == NULL)
> >                      continue;
> >
> > +                if (virHostdevFindUSBDevice(dev, true, &usb) < 0)
> > +                    continue;
> > +
>
> Shouldn't we rather fail in this case? Or, what happens if startupPolicy
> of the device is set to 'optional'? I think we need to error out here
> (although, we've probably errored out earlier in the process).
>

Hi,
sorry for the late reply, but I was finally getting some time off for a few
days.
I intentionally decided not to error out to avoid a new "source" of issues.
Compare the two options we have:
1. continue if not finding the device
  1.1 likely case we found it, rule will be correct - good
  1.2 we don't find it (for whatever reason) - we are "as bad" as before
this fix, but not worse
2. error out if not finding the device
  2.1 likely case we found it, rule will be correct - good
  2.2 we don't find it (for whatever reason) - we are now failing completely

What I don't like about 2.2 is that there might be cases things would have
been kind of ok, depsite whatever dark usb magic hit some special setup.
In those cases if we error out we add a new chance to fail.
And as there are often too many unknowns, so I chose the safer option.


> ACK to the rest of the patches (after some typo clean up, esp. in the
> commit messages).
>

Thanks,
do you want me to clean up commit messages or will somebody do (to his
preferred style) on accepting the commit?


> Michal
>



-- 
Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20171017/9a63d3b2/attachment-0001.htm>