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 trng_prop_fault_event_set, @errp is dereferenced without
ERRP_GUARD():

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

Currently, since trng_prop_fault_event_set() doesn't get the NULL @errp
parameter as a "set" method of object property, it hasn't triggered the
bug that dereferencing the NULL @errp.

And since visit_type_uint32() returns bool, check the returned bool
directly instead of dereferencing @errp, then we needn't the add missing
ERRP_GUARD().

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().
---
v2:
 * Add the @errp dereference code in commit message to make review
   easier. (Markus)
 * Check the returned bool instead of dereferencing @errp. (Markus)
---
 hw/misc/xlnx-versal-trng.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/hw/misc/xlnx-versal-trng.c b/hw/misc/xlnx-versal-trng.c
index b8111b8b6626..6495188dc748 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;
     }
 
-- 
2.34.1

On 23/2/24 09:56, Zhao Liu wrote:
> 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 trng_prop_fault_event_set, @errp is dereferenced without
> ERRP_GUARD():
> 
> visit_type_uint32(v, name, events, errp);
> if (*errp) {
>      return;
> }
> 
> Currently, since trng_prop_fault_event_set() doesn't get the NULL @errp
> parameter as a "set" method of object property, it hasn't triggered the
> bug that dereferencing the NULL @errp.
> 
> And since visit_type_uint32() returns bool, check the returned bool
> directly instead of dereferencing @errp, then we needn't the add missing
> ERRP_GUARD().
> 
> 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().
> ---
> v2:
>   * Add the @errp dereference code in commit message to make review
>     easier. (Markus)
>   * Check the returned bool instead of dereferencing @errp. (Markus)
> ---
>   hw/misc/xlnx-versal-trng.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>