Re: [PATCH 2/2] tracing: Add trace_trigger_soft_disabled() in front of trace_event_buffer_reserve() in trace_inject_entry()

[Steven Rostedt]

On Fri,  3 Sep 2021 03:30:34 +0000
Jiang Jiasheng <jiasheng@xxxxxxxxxxx> wrote:

> Directly use trace_event_buffer_reserve() might be unsafe,

How can it be unsafe?

> as we can see from the trace_trigger_soft_disabled() of
> 'include/linux/trace_events.h' that if the value of
> file->flags is 256, the check in the trace_trigger_soft_disabled()
> will be passed but actually shouldn't have.
> Therefore, we suggest that trace_trigger_soft_disabled()
> should be added in front of the trace_event_buffer_reserve()
> in trace_inject_entry().

Do you understand what the trace_inject_entry() does?

I'm not sure it makes sense to "soft disable" it.

> 
> Signed-off-by: Jiang Jiasheng <jiasheng@xxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_inject.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_inject.c b/kernel/trace/trace_events_inject.c
> index c188045..6dfd3cd 100644
> --- a/kernel/trace/trace_events_inject.c
> +++ b/kernel/trace/trace_events_inject.c
> @@ -21,6 +21,8 @@ trace_inject_entry(struct trace_event_file *file, void *rec, int len)
>  	void *entry;
>  
>  	rcu_read_lock_sched();
> +	if (trace_trigger_soft_disabled(file))
> +		return written;

NACK!

The above introduces a major bug. Bonus points if you can figure out
what that is yourself.

-- Steve

>  	entry = trace_event_buffer_reserve(&fbuffer, file, len);
>  	if (entry) {
>  		memcpy(entry, rec, len);