linux-kernel - [tip:perf/core] perf probe: Fix a segfault bug in debuginfo

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Date:	Thu, 1 Oct 2015 00:14:04 -0700
From:	tip-bot for Masami Hiramatsu <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	namhyung@...nel.org, hpa@...or.com,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org,
	linux-kernel@...r.kernel.org, acme@...hat.com, tglx@...utronix.de,
	wangnan0@...wei.com, mingo@...nel.org
Subject: [tip:perf/core] perf probe: Fix a segfault bug in debuginfo_cache

Commit-ID:  20f49859c785183d5296670a10dace454131274b
Gitweb:     http://git.kernel.org/tip/20f49859c785183d5296670a10dace454131274b
Author:     Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
AuthorDate: Thu, 1 Oct 2015 01:41:35 +0900
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Wed, 30 Sep 2015 18:34:36 -0300

perf probe: Fix a segfault bug in debuginfo_cache

perf probe --list will get a segfault if the first kprobe event is on a
module and the second or latter one is on the kernel.

e.g.
  ----
  # ./perf probe -q -m pcspkr pcspkr_event
  # ./perf probe -q vfs_read
  # ./perf probe -l
  Segmentation fault (core dumped)
  ----

This is because the debuginfo_cache fails to handle NULL module name,
which causes segfault on strcmp. (Note that strcmp("something", NULL)
always causes segfault)

To fix this debuginfo_cache__open always translates the NULL module name
to "kernel" (this is correct, because NULL module name means opening the
debuginfo for the kernel)

  ----
  # ./perf probe -l
    probe:pcspkr_event   (on pcspkr_event@...vers/input/misc/pcspkr.c
    in pcspkr)
    probe:vfs_read       (on vfs_read@...c/linux-3/fs/read_write.c)
  ----

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lkml.kernel.org/r/20150930164135.3733.23993.stgit@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/probe-event.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 65be284..3010abc 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -441,19 +441,22 @@ static char *debuginfo_cache_path;
 
 static struct debuginfo *debuginfo_cache__open(const char *module, bool silent)
 {
-	if ((debuginfo_cache_path && !strcmp(debuginfo_cache_path, module)) ||
-	    (!debuginfo_cache_path && !module && debuginfo_cache))
+	const char *path = module;
+
+	/* If the module is NULL, it should be the kernel. */
+	if (!module)
+		path = "kernel";
+
+	if (debuginfo_cache_path && !strcmp(debuginfo_cache_path, path))
 		goto out;
 
 	/* Copy module path */
 	free(debuginfo_cache_path);
-	if (module) {
-		debuginfo_cache_path = strdup(module);
-		if (!debuginfo_cache_path) {
-			debuginfo__delete(debuginfo_cache);
-			debuginfo_cache = NULL;
-			goto out;
-		}
+	debuginfo_cache_path = strdup(path);
+	if (!debuginfo_cache_path) {
+		debuginfo__delete(debuginfo_cache);
+		debuginfo_cache = NULL;
+		goto out;
 	}
 
 	debuginfo_cache = open_debuginfo(module, silent);
--
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