Re: [PATCH] hw/nubus/nubus-virtio-mmio: Fix missing ERRP_GUARD() in nubus_virtio_mmio_realize()

[Markus Armbruster <armbru@redhat.com>]

Zhao Liu <zhao1.liu@intel.com> writes:

> As the comment in qapi/error, dereferencing @errp requires

Suggest "According to the comment in qapi/error.h".

> ERRP_GUARD():
>
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> * - It must not be dereferenced, because it may be null.
> ...
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> *
> * Using it when it's not needed is safe, but please avoid cluttering
> * the source with useless code.
>
> But in nubus_virtio_mmio_realize(), @errp is dereferenced without
> ERRP_GUARD().

Suggest to scratch "But".

> Although nubus_virtio_mmio_realize() - as a DeviceClass.realize()
> method - doesn't get the NULL @errp parameter, it hasn't triggered the
> bug that dereferencing the NULL @errp. It's still necessary to follow
> the requirement of @errp, so add missing ERRP_GUARD() in
> nubus_virtio_mmio_realize().

Suggest

  Although nubus_virtio_mmio_realize() - as a DeviceClass.realize()
  method - is never passed a null @errp argument, it should follow the
  rules on @errp usage.  Add the ERRP_GUARD() there.
  
> Cc: Laurent Vivier <laurent@vivier.eu>
> Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  hw/nubus/nubus-virtio-mmio.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/nubus/nubus-virtio-mmio.c b/hw/nubus/nubus-virtio-mmio.c
> index 58a63c84d0be..a5558d3ec28b 100644
> --- a/hw/nubus/nubus-virtio-mmio.c
> +++ b/hw/nubus/nubus-virtio-mmio.c
> @@ -23,6 +23,7 @@ static void nubus_virtio_mmio_set_input_irq(void *opaque, int n, int level)
>  
>  static void nubus_virtio_mmio_realize(DeviceState *dev, Error **errp)
>  {
> +    ERRP_GUARD();
>      NubusVirtioMMIODeviceClass *nvmdc = NUBUS_VIRTIO_MMIO_GET_CLASS(dev);
>      NubusVirtioMMIO *s = NUBUS_VIRTIO_MMIO(dev);
>      NubusDevice *nd = NUBUS_DEVICE(dev);
       SysBusDevice *sbd;
       int i, offset;

       nvmdc->parent_realize(dev, errp);

Here's the dereference:

       if (*errp) {
           return;
       }

Reviewed-by: Markus Armbruster <armbru@redhat.com>

Thanks!