Re: [PATCH 4/6] hw/misc/xlnx-versal-trng: Fix missing ERRP_GUARD() in trng_prop_fault_event_set()

[Markus Armbruster]

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

> 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.
> * - It should not be passed to error_prepend() 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.
> *
> * Using it when it's not needed is safe, but please avoid cluttering
> * the source with useless code.
>
> Currently, since trng_prop_fault_event_set() doesn't get the NULL errp
> parameter as a "set" method of object property, it doesn't trigger the
> dereference issue.
>
> To follow the requirement of errp, add missing ERRP_GUARD() in
> trng_prop_fault_event_set().
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Suggested by credit:
>  Markus: Referred his explanation about ERRP_GUARD().
> ---
>  hw/misc/xlnx-versal-trng.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/hw/misc/xlnx-versal-trng.c b/hw/misc/xlnx-versal-trng.c
> index b8111b8b6626..3579348a9d17 100644
> --- a/hw/misc/xlnx-versal-trng.c
> +++ b/hw/misc/xlnx-versal-trng.c
> @@ -33,6 +33,7 @@
>  #include "qemu/error-report.h"
>  #include "qemu/guest-random.h"
>  #include "qemu/timer.h"
> +#include "qapi/error.h"
>  #include "qapi/visitor.h"
>  #include "migration/vmstate.h"
>  #include "hw/qdev-properties.h"
> @@ -641,6 +642,7 @@ static void trng_prop_fault_event_set(Object *obj, 
> Visitor *v,
>                                        const char *name, void *opaque,
>                                        Error **errp)
>  {
> +    ERRP_GUARD();
>      Property *prop = opaque;
>      uint32_t *events = object_field_prop_ptr(obj, prop);

       visit_type_uint32(v, name, events, errp);
       if (*errp) {
           return;
       }

Please do this instead:

diff --git a/hw/misc/xlnx-versal-trng.c b/hw/misc/xlnx-versal-trng.c
index b8111b8b66..6495188dc7 100644
--- a/hw/misc/xlnx-versal-trng.c
+++ b/hw/misc/xlnx-versal-trng.c
@@ -644,8 +644,7 @@ static void trng_prop_fault_event_set(Object *obj, Visitor 
*v,
     Property *prop = opaque;
     uint32_t *events = object_field_prop_ptr(obj, prop);
 
-    visit_type_uint32(v, name, events, errp);
-    if (*errp) {
+    if (!visit_type_uint32(v, name, events, errp)) {
         return;
     }