linux-kernel - Re: [PATCH] perf session: Correct buffer copying when peek event

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Date:   Tue, 8 Jun 2021 13:07:22 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf session: Correct buffer copying when peek event

On Sat, Jun 05, 2021 at 01:29:57PM +0800, Leo Yan wrote:
> When peek an event, it has a short path and a long path.  The short path
> uses the session pointer "one_mmap_addr" to directly fetch event; and
> the long path needs to read out the event header and the followed event
> data from file and fill into the buffer pointer passed through the
> argument "buf".
> 
> The issue is in the long path that it copies the event header and event
> data into the same destination address which pointer "buf", this means
> the event header is overwritten.  We are just lucky to run into the
> short path in most cases, so we don't hit the issue in the long path.
> 
> This patch adds the offset "hdr_sz" to the pointer "buf" when copying
> the event data, so that it can reserve the event header which can be
> used properly by its caller.
> 
> Fixes: 5a52f33adf02 ("perf session: Add perf_session__peek_event()")
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/session.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 106b3d60881a..e59242c361ce 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1723,6 +1723,7 @@ int perf_session__peek_event(struct perf_session *session, off_t file_offset,
>  	if (event->header.size < hdr_sz || event->header.size > buf_sz)
>  		return -1;
>  
> +	buf += hdr_sz;

nice ;-)

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

>  	rest = event->header.size - hdr_sz;
>  
>  	if (readn(fd, buf, rest) != (ssize_t)rest)
> -- 
> 2.25.1
>