On Fri, 23 Feb 2024 16:56:47 +0800
Zhao Liu <zhao1....@linux.intel.com> wrote:
> From: Zhao Liu <zhao1....@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 cxl_fixed_memory_window_config(), @errp is dereferenced in 2
> places without ERRP_GUARD():
>
> fw->enc_int_ways = cxl_interleave_ways_enc(fw->num_targets, errp);
> if (*errp) {
> return;
> }
>
> and
>
> fw->enc_int_gran =
> cxl_interleave_granularity_enc(object->interleave_granularity,
> errp);
> if (*errp) {
> return;
> }
>
> For the above 2 places, we check "*errp", because neither function
> returns a suitable error code. And since machine_set_cfmw() - the caller
> of cxl_fixed_memory_window_config() - doesn't get the NULL @errp
> parameter as the "set" method of object property,
> cxl_fixed_memory_window_config() hasn't triggered the bug that
> dereferencing the NULL @errp.
>
> To follow the requirement of @errp, add missing ERRP_GUARD() in
> cxl_fixed_memory_window_config().
>
> Suggested-by: Markus Armbruster <arm...@redhat.com>
> Signed-off-by: Zhao Liu <zhao1....@intel.com>
> Reviewed-by: Markus Armbruster <arm...@redhat.com>
Acked-by: Jonathan Cameron <jonathan.came...@huawei.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)
> ---
> hw/cxl/cxl-host.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
> index 2aa776c79c74..c5f5fcfd64d0 100644
> --- a/hw/cxl/cxl-host.c
> +++ b/hw/cxl/cxl-host.c
> @@ -26,6 +26,7 @@ static void cxl_fixed_memory_window_config(CXLState
> *cxl_state,
> CXLFixedMemoryWindowOptions
> *object,
> Error **errp)
> {
> + ERRP_GUARD();
> g_autofree CXLFixedWindow *fw = g_malloc0(sizeof(*fw));
> strList *target;
> int i;
