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

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Date:	Fri, 07 Aug 2009 11:24:27 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tracing/filters: Support filtering for char * strings

Steven Rostedt wrote:
> On Fri, 7 Aug 2009, Li Zefan wrote:
>>> What protection is this giving us?
>>>
>> __field(char *) suggests it should be treated as plain pointer,
>> while __field_ext(char *, FILTER_PTR_STR) suggests he's aware it's
>> safe to dereference the pointer, for example the case in Frederic's
>> blk events.
>>
>> In Frederic's initial version, "char *" field will always be
>> attached to ptr_str filter function. This is unsafe, because for
>> other fields defined as "char *" but not safe to dereference,
>> a user still can do this:
>>
>> 	# echo 'name == abc' > filter
>>
>> Then we'll deref a pointer that can point to unsafe data.
>>
>> In this patch, this won't happen, as long as the developer is
>> aware that his use of __field_ext(char *) is right.
>>
>> Otherwise, he will just use normal __field(char *) and print
>> the pointer itself in TP_printk().
> 
> Ah, so the answer I'm looking for is:
> 
> The filtering will not dereference "char *" unless the developer 
> explicitly sets FILTER_PTR_STR in __field_ext.
> 
> Is this above statement correct?
> 

Exactly. Sorry that I didn't explain it clearly in the
first place. :)

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