Re: [PULL 34/68] hw/display/macfb: Fix missing ERRP_GUARD() in macfb_nubus_realize()

[Zhao Liu]

Hi Michael,

Thanks a lot and aslo this one, I forgot to update the status :/,
this patch has been merged (commit d470fd6acd60, "hw/display/macfb:
Fix missing ERRP_GUARD() in macfb_nubus_realize()").

Best Regards,
Zhao


On Tue, Mar 12, 2024 at 06:27:16PM -0400, Michael S. Tsirkin wrote:
> Date: Tue, 12 Mar 2024 18:27:16 -0400
> From: "Michael S. Tsirkin" <mst@redhat.com>
> Subject: [PULL 34/68] hw/display/macfb: Fix missing ERRP_GUARD() in
>  macfb_nubus_realize()
> X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1
> 
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> As the comment in qapi/error, dereferencing @errp requires
> 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 macfb_nubus_realize(), @errp is dereferenced without
> ERRP_GUARD():
> 
> ndc->parent_realize(dev, errp);
> if (*errp) {
>     return;
> }
> 
> Here we check *errp, because the ndc->parent_realize(), as a
> DeviceClass.realize() callback, returns void. And since
> macfb_nubus_realize(), also as a DeviceClass.realize(), doesn't get the
> NULL @errp parameter, it hasn't triggered the bug that dereferencing the
> NULL @errp.
> 
> To follow the requirement of @errp, add missing ERRP_GUARD() in
> macfb_nubus_realize().
> 
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Message-Id: <20240223085653.1255438-3-zhao1.liu@linux.intel.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/display/macfb.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/display/macfb.c b/hw/display/macfb.c
> index 418e99c8e1..1ace341a0f 100644
> --- a/hw/display/macfb.c
> +++ b/hw/display/macfb.c
> @@ -714,6 +714,7 @@ static void macfb_nubus_set_irq(void *opaque, int n, int 
> level)
>  
>  static void macfb_nubus_realize(DeviceState *dev, Error **errp)
>  {
> +    ERRP_GUARD();
>      NubusDevice *nd = NUBUS_DEVICE(dev);
>      MacfbNubusState *s = NUBUS_MACFB(dev);
>      MacfbNubusDeviceClass *ndc = NUBUS_MACFB_GET_CLASS(dev);
> -- 
> MST
>