tracing/probe: Check event name length correctly

Ensure given name of event is not too long when parsing it,
and fix to update event name offset correctly when the group
name is given. For example, this makes probe event to check
the "p:foo/" error case correctly.

Link: http://lkml.kernel.org/r/155253782046.14922.14724124823730168629.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_probe.c

@@ -159,6 +159,7 @@ int traceprobe_parse_event_name(const char **pevent, const char **pgroup,
 				char *buf)
 {
 	const char *slash, *event = *pevent;
+	int len;
 
 	slash = strchr(event, '/');
 	if (slash) {
@@ -173,10 +174,15 @@ int traceprobe_parse_event_name(const char **pevent, const char **pgroup,
 		strlcpy(buf, event, slash - event + 1);
 		*pgroup = buf;
 		*pevent = slash + 1;
+		event = *pevent;
 	}
-	if (strlen(event) == 0) {
+	len = strlen(event);
+	if (len == 0) {
 		pr_info("Event name is not specified\n");
 		return -EINVAL;
+	} else if (len > MAX_EVENT_NAME_LEN) {
+		pr_info("Event name is too long\n");
+		return -E2BIG;
 	}
 	return 0;
 }