Re: [Qemu-devel][PATCH] ppc/spapr_events: fix potential NULL pointer dereference in rtas_event_log_dequeue

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Nov 18, 2019 at 09:50:13AM +0800, pannengyuan@huawei.com wrote:
> From: PanNengyuan <pannengyuan@huawei.com>
> 
> source is being dereferenced before it is null checked, hence there is a
> potential null pointer dereference.
> 
> This fixes:
>         360
>     CID 68911917: (NULL_RETURNS)
>         361. dereference: Dereferencing "source", which is known to be
>         "NULL".
>         361        if (source->mask & event_mask) {
>         362            break;
>         363        }
> 
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: PanNengyuan <pannengyuan@huawei.com>

I don't think this is the right solution.  The only events we ever
generated are LOG_TYPE_EPOW and LOG_TYPE_HOTPLUG, so in fact source
should never be NULL.

I think the correct way to satisfy Coverity here is to have
rtas_event_log_to_source() do an assert(), rather than returning NULL
for other event types.

> ---
>  hw/ppc/spapr_events.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> index 0e4c195..febd2ef 100644
> --- a/hw/ppc/spapr_events.c
> +++ b/hw/ppc/spapr_events.c
> @@ -358,7 +358,7 @@ static SpaprEventLogEntry *rtas_event_log_dequeue(SpaprMachineState *spapr,
>              rtas_event_log_to_source(spapr,
>                                       spapr_event_log_entry_type(entry));
>  
> -        if (source->mask & event_mask) {
> +        if (source && (source->mask & event_mask)) {
>              break;
>          }
>      }

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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