linux-kernel - [PATCH v2] ftrace: unsigned idx cannot be less than 0

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Date:	Sat, 03 Jan 2009 16:55:50 +0100
From:	Roel Kluin <roel.kluin@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: [PATCH v2] ftrace: unsigned idx cannot be less than 0

>>>> -		if (iter->idx < 0)
>>>> +		if (iter->idx == 0)

>>> I'm not sure this is the right fix.
>>> If you look at t_next, if there is no more page to look at,
>>> iter_idx takes -1.
>>>
>>> A 0 value would mean: we are in the first index on the page, which means
>>> there is something to read and we don't want to return NULL.
>>>
>>> I guess that would be better to turn idx into a signed int.

>> If we turn idx in a signed int, isn't it true that
>> in kernel/trace/ftrace.c, line 806:

>> since iter->pg->index is an unsigned long, when larger than INT_MAX this
>> could result in an endless loop?
> 
> Actually, this is not supposed to reach such a threshold.
> Looks like it wouldn't increase over ENTRIES_PER_PAGE (defined
> in ftrace.c) which is smaller than PAGE_SIZE.
> So it will stay far from an overflow.

unless signed idx cannot become less than 0

Signed-off-by: Roel Kluin <roel.kluin@...il.com>
---
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2f32969..e256648 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -786,7 +786,7 @@ enum {
 
 struct ftrace_iterator {
 	struct ftrace_page	*pg;
-	unsigned		idx;
+	int			idx;
 	unsigned		flags;
 	unsigned char		buffer[FTRACE_BUFF_MAX+1];
 	unsigned		buffer_idx;

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