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

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* 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.

ERRP_GUARD() could avoid the case when @errp is &error_fatal, the user
can't see this additional information, because exit() happens in
error_setg earlier than information is added [1].

The vfio_ap_realize() passes @errp to error_prepend(), and as a
DeviceClass.realize method, there are too many possible callers to check
the impact of this defect; it may or may not be harmless. Thus it is
necessary to protect @errp with ERRP_GUARD().

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: "Cédric Le Goater" <clg@redhat.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Jason Herne <jjherne@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: qemu-s390x@nongnu.org
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
v2: Use Markus' sentence to polish commit message. (Markus)
---
 hw/vfio/ap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
index e157aa1ff79c..7c4caa593863 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -155,6 +155,7 @@ static void vfio_ap_unregister_irq_notifier(VFIOAPDevice *vapdev,
 
 static void vfio_ap_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     int ret;
     Error *err = NULL;
     VFIOAPDevice *vapdev = VFIO_AP_DEVICE(dev);
-- 
2.34.1

On 3/11/24 04:38, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> As the comment in qapi/error, passing @errp to error_prepend() requires
> ERRP_GUARD():
> 
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> ...
> * - It should not be passed to error_prepend(), error_vprepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * 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.
> 
> ERRP_GUARD() could avoid the case when @errp is &error_fatal, the user
> can't see this additional information, because exit() happens in
> error_setg earlier than information is added [1].
> 
> The vfio_ap_realize() passes @errp to error_prepend(), and as a
> DeviceClass.realize method, there are too many possible callers to check
> the impact of this defect; it may or may not be harmless. Thus it is
> necessary to protect @errp with ERRP_GUARD().
> 
> To avoid the issue like [1] said, add missing ERRP_GUARD() at the
> beginning of this function.
> 
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>       ("error: New macro ERRP_GUARD()").
> 
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: "Cédric Le Goater" <clg@redhat.com>
> Cc: Tony Krowiak <akrowiak@linux.ibm.com>
> Cc: Halil Pasic <pasic@linux.ibm.com>
> Cc: Jason Herne <jjherne@linux.ibm.com>
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: qemu-s390x@nongnu.org
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
> v2: Use Markus' sentence to polish commit message. (Markus)
> ---
>   hw/vfio/ap.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
> index e157aa1ff79c..7c4caa593863 100644
> --- a/hw/vfio/ap.c
> +++ b/hw/vfio/ap.c
> @@ -155,6 +155,7 @@ static void vfio_ap_unregister_irq_notifier(VFIOAPDevice *vapdev,
>   
>   static void vfio_ap_realize(DeviceState *dev, Error **errp)
>   {
> +    ERRP_GUARD();
>       int ret;
>       Error *err = NULL;
>       VFIOAPDevice *vapdev = VFIO_AP_DEVICE(dev);