linux-kernel - Re: [PATCH] tools lib traceevent: Fix kbuffer_read_at

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Date:   Wed, 5 Oct 2016 09:28:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools lib traceevent: Fix kbuffer_read_at_offset()

On Sat,  1 Oct 2016 19:17:00 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> When it's called with an offset less than or equal to the first event,
> it'll return a garbage value since the data is not initialized.

Well, it can at most be equal to (unless offset is negative) because
kbuffer_load_subbuffer() sets kbuf->curr to zero.

But that said, it looks like offset == 0 is buggy.

Acked-by: Steven Rostedt <rostedt@...dmis.org>


-- Steve

> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/traceevent/kbuffer-parse.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/lib/traceevent/kbuffer-parse.c b/tools/lib/traceevent/kbuffer-parse.c
> index 3bcada3ae05a..65984f1c2974 100644
> --- a/tools/lib/traceevent/kbuffer-parse.c
> +++ b/tools/lib/traceevent/kbuffer-parse.c
> @@ -622,6 +622,7 @@ void *kbuffer_read_at_offset(struct kbuffer *kbuf, int offset,
>  
>  	/* Reset the buffer */
>  	kbuffer_load_subbuffer(kbuf, kbuf->subbuffer);
> +	data = kbuffer_read_event(kbuf, ts);
>  
>  	while (kbuf->curr < offset) {
>  		data = kbuffer_next_event(kbuf, ts);