linux-kernel - Re: [PATCH v3 1/3] bpf: Add new bpf map type to store the pointer to struct perf

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Message-ID: <55B170AC.30009@plumgrid.com>
Date:	Thu, 23 Jul 2015 15:54:36 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org
Cc:	wangnan0@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v3 1/3] bpf: Add new bpf map type to store the pointer to
 struct perf_event

On 7/23/15 2:42 AM, Kaixu Xia wrote:
> Introduce a new bpf map type 'BPF_MAP_TYPE_PERF_EVENT_ARRAY'.
> This map only stores the pointer to struct perf_event. The
> user space event FDs from perf_event_open() syscall are converted
> to the pointer to struct perf_event and stored in map.
...
> +static struct bpf_map *perf_event_array_map_alloc(union bpf_attr *attr)
> +{
> +	/* only the pointer to struct perf_event can be stored in
> +	 * perf_event_array map
> +	 */
> +	if (attr->value_size != sizeof(u32))
> +		return ERR_PTR(-EINVAL);
> +
> +	return array_map_alloc(attr);
> +}

since it's exactly the same as prog_array_map_alloc(),
just rename it to something like 'fd_array_map_alloc'
and use for both types.

> +static int perf_event_array_map_get_next_key(struct bpf_map *map, void *key,
> +					     void *next_key)
> +{
> +	return -EINVAL;
> +}
> +
> +static void *perf_event_array_map_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	return NULL;
> +}

same for the above two.
rename prog_array_map_* into fd_array_map_* and use for both map types.

> +static struct perf_event *convert_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 NULL;

don't lose error code, do 'return event' instead.

> +
> +	/* limit the event type to PERF_TYPE_RAW
> +	 * and PERF_TYPE_HARDWARE.
> +	 */
> +	if (event->attr.type != PERF_TYPE_RAW &&
> +	    event->attr.type != PERF_TYPE_HARDWARE)
> +		return NULL;

perf_event refcnt leak? need to do put_event.
and return ERR_PTR(-EINVAL)

> +
> +	return event;
> +}
> +
> +/* only called from syscall */
> +static int perf_event_array_map_update_elem(struct bpf_map *map, void *key,
> +					    void *value, u64 map_flags)
> +{
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	struct perf_event *event;
> +	u32 index = *(u32 *)key;
> +
> +	if (map_flags != BPF_ANY)
> +		return -EINVAL;
> +
> +	if (index >= array->map.max_entries)
> +		return -E2BIG;
> +
> +	/* check if the value is already stored */
> +	if (array->events[index])
> +		return -EINVAL;
> +
> +	/* convert the fd to the pointer to struct perf_event */
> +	event = convert_map_with_perf_event(value);

imo helper name is misleading and it's too short to be separate
function. Just inline it and you can reuse 'index' variable.

> +	if (!event)
> +		return -EBADF;
> +
> +	xchg(array->events + index, event);

refcnt leak of old event! Please think it through.
This type of bugs I shouldn't be finding.

> +static int perf_event_array_map_delete_elem(struct bpf_map *map, void *key)
> +{
> +	return -EINVAL;
> +}

no way to dec refcnt of perf_event from user space?
why not to do the same as prog_array_delete?

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