[PATCH 5/5] qemu_validate: Deduplicate code for graphics type check

[Peter Krempa]

On Wed, Nov 18, 2020 at 09:12:26 +0100, Michal Privoznik wrote:
> On 11/18/20 8:59 AM, Peter Krempa wrote:
> > On Tue, Nov 17, 2020 at 12:28:27 +0100, Michal Privoznik wrote:
> > > Similarly to previous commits, we can utilize domCaps to check if
> > > graphics type is supported.
> > > 
> > > Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> > > ---
> > >   src/qemu/qemu_capabilities.c |  2 +-
> > >   src/qemu/qemu_capabilities.h |  3 +++
> > >   src/qemu/qemu_validate.c     | 40 ++++++++++++------------------------
> > >   3 files changed, 17 insertions(+), 28 deletions(-)
> > 
> > [...]
> > 
> > > @@ -3903,15 +3892,12 @@ qemuValidateDomainDeviceDefGraphics(const virDomainGraphicsDef *graphics,
> > >           }
> > >           break;
> > > +
> > > +    case VIR_DOMAIN_GRAPHICS_TYPE_VNC:
> > >       case VIR_DOMAIN_GRAPHICS_TYPE_RDP:
> > >       case VIR_DOMAIN_GRAPHICS_TYPE_DESKTOP:
> > > -        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> > > -                       _("unsupported graphics type '%s'"),
> > > -                       virDomainGraphicsTypeToString(graphics->type));
> > > -        return -1;
> > >       case VIR_DOMAIN_GRAPHICS_TYPE_LAST:
> > > -    default:
> > > -        return -1;
> > > +        break;
> > 
> > Removing 'default: ' is not necessary once you use proper type for the
> > variable in the switch statement, which is our usual approach.
> 
> I guess I don't need to typecast ->type since it's already stored as
> virDomainGraphicsType in the struct.
> 
> > 
> > The default and _LAST case should use virReportEnumRangeError.
> > 
> > 
> 
> I'm not sure it's adding useful code. In this very patch I'm adding a check
> that rejects unknown values for ->type and thus I don't see a way how the
> control could hit any of these 'case', or 'default'.

You are right it won't .

A drawback of using the capability code is that
it relies on converting the type to a bit array stored in "unsigned int"
without any overflow safeguards. Once a device model or type enum
reaches 33 entries, the code will start failing without any obvious
sign.

virDomainCapsEnumSet which is internally used by the VIR_DOMAIN_CAPS_ENUM_SET
which is used by virQEMUCapsFillDomainDeviceGraphicsCaps to fill the
bitmap catches overflow but the callers neglect to propagate it.