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

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Date:	Thu, 6 Aug 2009 23:22:54 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Li Zefan <lizf@...fujitsu.com>
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


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?

-- Steve

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