perf parse-events: Add defensive NULL check

Terms may have a NULL config in which case a strcmp will SEGV. This can
be reproduced with:

  perf stat -e '*/event=?,nr/' sleep 1

Add a NULL check to avoid this. This was caught by LLVM's libfuzzer.

Signed-off-by: Ian Rogers <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Jin Yao <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Garry <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: [email protected]
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: captain5050

tools/perf/util/pmu.c

@@ -984,12 +984,11 @@ static int pmu_resolve_param_term(struct parse_events_term *term,
 	struct parse_events_term *t;
 
 	list_for_each_entry(t, head_terms, list) {
-		if (t->type_val == PARSE_EVENTS__TERM_TYPE_NUM) {
-			if (!strcmp(t->config, term->config)) {
-				t->used = true;
-				*value = t->val.num;
-				return 0;
-			}
+		if (t->type_val == PARSE_EVENTS__TERM_TYPE_NUM &&
+		    t->config && !strcmp(t->config, term->config)) {
+			t->used = true;
+			*value = t->val.num;
+			return 0;
 		}
 	}