linux-kernel - Re: [PATCH] coresight: Fix uninitialised pointer bug in etm_setup

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Date:   Thu, 29 Oct 2020 10:30:17 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org, suzuki.poulose@....com,
        alexander.shishkin@...ux.intel.com, lcherian@...vell.com
Subject: Re: [PATCH] coresight: Fix uninitialised pointer bug in
 etm_setup_aux()

On Wed, Oct 28, 2020 at 05:43:01PM +0000, Mike Leach wrote:
> Commit [bb1860efc817] changed the sink handling code introducing an
> uninitialised pointer bug. This results in the default sink selection
> failing.
> 
> Prior to commit:
> 
> static void etm_setup_aux(...)
> 
> <snip>
>         struct coresight_device *sink;
> <snip>
> 
>         /* First get the selected sink from user space. */
>         if (event->attr.config2) {
>                 id = (u32)event->attr.config2;
>                 sink = coresight_get_sink_by_id(id);
>         } else {
>                 sink = coresight_get_enabled_sink(true);
>         }
> <ctd>
> 
> *sink always initialised - possibly to NULL which triggers the
> automatic sink selection.
> 
> After commit:
> 
> static void etm_setup_aux(...)
> 
> <snip>
>         struct coresight_device *sink;
> <snip>
> 
>         /* First get the selected sink from user space. */
>         if (event->attr.config2) {
>                 id = (u32)event->attr.config2;
>                 sink = coresight_get_sink_by_id(id);
>         }
> <ctd>
> 
> *sink pointer uninitialised when not providing a sink on the perf command
> line. This breaks later checks to enable automatic sink selection.
> 
> Fixes [bb1860efc817] ("coresight: etm: perf: Sink selection using sysfs is deprecated")
> Signed-off-by: Mike Leach <mike.leach@...aro.org>
> ---
>  drivers/hwtracing/coresight/coresight-etm-perf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index c2c9b127d074..bdc34ca449f7 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -210,7 +210,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
>  	u32 id;
>  	int cpu = event->cpu;
>  	cpumask_t *mask;
> -	struct coresight_device *sink;
> +	struct coresight_device *sink = NULL;

Yes, obviously - thanks for catching that.

As checkpatch has complained about, the Fixes line you added isn't correct.  It
should have been:

Fixes: bb1860efc817 ("coresight: etm: perf: Sink selection using sysfs is deprecated")

I made the modification and applied to my tree.

Thanks,
Mathieu

>  	struct etm_event_data *event_data = NULL;
>  
>  	event_data = alloc_event_data(cpu);
> -- 
> 2.17.1
>