Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf()

[Peter Zijlstra]

On Thu, Oct 22, 2020 at 04:27:52PM +0530, Sai Prakash Ranjan wrote:

> Looking at the ETR and other places in the kernel, ETF and the
> ETB are the only places trying to dereference the task(owner)
> in tmc_enable_etf_sink_perf() which is also called from the
> sched_in path as in the call trace.

> @@ -391,6 +392,10 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev,
>  {
>  	int node;
>  	struct cs_buffers *buf;
> +	struct task_struct *task = READ_ONCE(event->owner);
> +
> +	if (!task || is_kernel_event(event))
> +		return NULL;


This is *wrong*... why do you care about who owns the events?