linux-kernel - [PATCH 1/2] perf record: Don't try to find buildids in a zero sized file

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Date:	Thu, 11 Mar 2010 15:53:11 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, stable@...nel.org
Subject: [PATCH 1/2] perf record: Don't try to find buildids in a zero sized file

From: Arnaldo Carvalho de Melo <acme@...hat.com>

Fixing this symptom:

[acme@...a linux-2.6-tip]$ perf record -a -f
  Fatal: Permission error - are you root?

Bus error
[acme@...a linux-2.6-tip]$

I.e. if for some reason no data is collected, in this case a non root user
trying to do systemwide profiling, no data will be collected, and then we end
up trying to mmap a zero sized file and access the file header, b00m.

Reported-by: Ingo Molnar <mingo@...e.hu>
Cc: Frédéric Weisbecker <fweisbec@...il.com>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: stable@...nel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-record.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f573bbb..3bf1409 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -394,6 +394,9 @@ static int process_buildids(void)
 {
 	u64 size = lseek(output, 0, SEEK_CUR);
 
+	if (size == 0)
+		return 0;
+
 	session->fd = output;
 	return __perf_session__process_events(session, post_processing_offset,
 					      size - post_processing_offset,
-- 
1.5.5.1

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