linux-kernel - [PATCH 4.14] perf machine: Guard against NULL in machine_

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Message-ID: <20190619120030.6099-1-tommi.t.rantala@nokia.com>
Date:   Wed, 19 Jun 2019 12:00:46 +0000
From:   "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@...ia.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH 4.14] perf machine: Guard against NULL in machine__exit()

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

commit 4a2233b194c77ae1ea8304cb7c00b551de4313f0 upstream.

A recent fix for 'perf trace' introduced a bug where
machine__exit(trace->host) could be called while trace->host was still
NULL, so make this more robust by guarding against NULL, just like
free() does.

The problem happens, for instance, when !root users try to run 'perf
trace':

  [acme@...et linux]$ trace
  Error:	No permissions to read /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
  Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'

  perf: Segmentation fault
  Obtained 7 stack frames.
  [0x4f1b2e]
  /lib64/libc.so.6(+0x3671f) [0x7f43a1dd971f]
  [0x4f3fec]
  [0x47468b]
  [0x42a2db]
  /lib64/libc.so.6(__libc_start_main+0xe9) [0x7f43a1dc3509]
  [0x42a6c9]
  Segmentation fault (core dumped)
  [acme@...et linux]$

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andrei Vagin <avagin@...nvz.org>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Vasily Averin <vvs@...tuozzo.com>
Cc: Wang Nan <wangnan0@...wei.com>
Fixes: 33974a414ce2 ("perf trace: Call machine__exit() at exit")
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Tommi Rantala <tommi.t.rantala@...ia.com>
---
 tools/perf/util/machine.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 968fd0454e6b..d246080cd85e 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -156,6 +156,9 @@ void machine__delete_threads(struct machine *machine)
 
 void machine__exit(struct machine *machine)
 {
+	if (machine == NULL)
+		return;
+
 	machine__destroy_kernel_maps(machine);
 	map_groups__exit(&machine->kmaps);
 	dsos__exit(&machine->dsos);
-- 
2.20.1