Re: [PATCH 3/3] tracing/filters: Support filtering for char * strings

[Li Zefan <lizf@cn.fujitsu.com>]

>>  	if (is_string_field(field)) {
>> +		pred->str_len = field->size;
>> +
>>  		if (field->filter_type == FILTER_STATIC_STRING)
>>  			fn = filter_pred_string;
>> -		else
>> +		else if (field->filter_type == FILTER_DYN_STRING)
>>  			fn = filter_pred_strloc;
>> -		pred->str_len = field->size;
>> +		else {
>> +			fn = filter_pred_pchar;
>> +			pred->str_len = strlen(pred->str_val);
>> +		}
> 
> I'm a little dense here, where do we protect against someone making a 
> tracepoint that points to unsafe data?
> 

We can't prevent anyone from doing insane things deliberately, but
we prevent from doing wrong things unconsciously.

Only if a TRACE_EVENT has a field defined as:

	__field_ext(char *, name, FILTER_PTR_STR)

Here using FILTER_PTR_STR explicitly, he should know what he's doing.

Anyway, he can make a ptr pointing to unsafe data this way:

	TP_STRUCT__entry(
		__field(char *, name)
	)
	TP_printk("%s", name)