linux-kernel - Re: [PATCH 3/5] blktrace: fix off-by-one bug

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Date:	Tue, 24 Mar 2009 09:27:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] blktrace: fix off-by-one bug


* Li Zefan <lizf@...fujitsu.com> wrote:

> 'what' is used as the index of array what2act, so it can't >= the array size.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/trace/blktrace.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 9af4143..0e91caa 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1149,7 +1149,7 @@ static enum print_line_t blk_trace_event_print(struct trace_iterator *iter,
>  	if (!trace_print_context(iter))
>  		return TRACE_TYPE_PARTIAL_LINE;
>  
> -	if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
> +	if (unlikely(what == 0 || what >= ARRAY_SIZE(what2act)))
>  		ret = trace_seq_printf(s, "Bad pc action %x\n", what);
>  	else {
>  		const bool long_act = !!(trace_flags & TRACE_ITER_VERBOSE);
> @@ -1196,7 +1196,7 @@ static enum print_line_t blk_tracer_print_line(struct trace_iterator *iter)
>  	t = (const struct blk_io_trace *)iter->ent;
>  	what = t->action & ((1 << BLK_TC_SHIFT) - 1);
>  
> -	if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))
> +	if (unlikely(what == 0 || what >= ARRAY_SIZE(what2act)))

ah, nice. How did you notice - did we miss "remap" events due to 
this bug?

	Ingo
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