Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 17, 2015 at 06:43:33PM +0800, kaixu xia wrote:
> +static int replace_map_with_perf_event(void *value)
> +{
> +	struct perf_event *event;
> +	u32 fd;
> +
> +	fd = *(u32 *)value;
> +
> +	event = perf_event_get(fd);
> +	if (IS_ERR(event))
> +		return PTR_ERR(event);
> +

And userspace closes here,

> +	if (atomic_long_inc_not_zero(&event->refcount))

And this goes *BOOM*

> +		memcpy(value, &event, sizeof(struct perf_event *));
> +	else
> +		return -ENOENT;
> +
> +	return 0;
> +}

Also, why do you think its OK to prod around the internals of perf_event
outside of kernel/events/ ?