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Date:   Tue, 8 Jun 2021 09:47:54 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Leo Yan <leo.yan@linaro.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf session: Correct buffer copying when peek event
Message-ID: <YL9m+liygPxoa5bu@kernel.org>
References: <20210605052957.1070720-1-leo.yan@linaro.org>
 <YL9PatslajgTZpZM@krava>
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Em Tue, Jun 08, 2021 at 01:07:22PM +0200, Jiri Olsa escreveu:
> 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@linaro.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@redhat.com>

Thanks, applied.

- Arnaldo