[PATCH] perf: probe: avoid segfault if passed with ''.

[Wang Nan <wangnan0@huawei.com>]

Since parse_perf_probe_point() deals with a user passed argument, we
should not assume it to be a valid string.

Without this patch, if pass '' to perf probe, a segfault raises:

 $ perf probe -a ''
 Segmentation fault

This patch checks argument of parse_perf_probe_point() before
string processing.

After this patch:

 $ perf probe -a ''

  usage: perf probe [<options>] 'PROBEDEF' ['PROBEDEF' ...]
     or: perf probe [<options>] --add 'PROBEDEF' [--add 'PROBEDEF' ...]
     ...

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
 tools/perf/util/probe-event.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index d8bb616..d05b77c 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1084,6 +1084,8 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
 	 *
 	 * TODO:Group name support
 	 */
+	if (!arg)
+		return -EINVAL;
 
 	ptr = strpbrk(arg, ";=@+%");
 	if (ptr && *ptr == '=') {	/* Event name */
-- 
1.8.3.4