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

[Sai Prakash Ranjan]

On 2020-10-22 19:04, Peter Zijlstra wrote:
> On Thu, Oct 22, 2020 at 06:19:37PM +0530, Sai Prakash Ranjan wrote:
> > On 2020-10-22 17:02, Peter Zijlstra wrote:
> > > 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?
> > >
> >
> > The original issue was the owner being NULL and causing
> > a NULL pointer dereference. I did ask some time back
> > if it is valid for the owner to be NULL [1] and should
> > probably be handled in events core?
>
> No, what I asked is why do you care about ->owner to begin with? That
> seems wrong. A driver should not touch ->owner _at_all_.

Ah ok, so Suzuki explained that in other reply and if there is
some other better way?

Thanks,
Sai

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