[PATCH v1] perf parse-events: Avoid segv if PMU lookup fails for legacy cache terms

[Ian Rogers <irogers@google.com>]

libfuzzer found the following command could segv:
```
$ perf stat -e cpu/L2,L2/ true
```
This is because the L2 term rewrites the perf_event_attr type to
PERF_TYPE_HW_CACHE which then fails the PMU lookup for the second
legacy cache term.

The new failure is consistent with repeated hardware terms:
```
$ perf stat -e cpu/L2,L2/ true
event syntax error: 'cpu/L2,L2/'
                            \___ Failed to find PMU for type 3

Initial error:
event syntax error: 'cpu/L2,L2/'
                            \___ Failed to find PMU for type 3
Run 'perf list' for a list of valid events

 Usage: perf stat [<options>] [<command>]

    -e, --event <event>   event selector. use 'perf list' to list available events
$ perf stat -e cpu/cycles,cycles/ true
event syntax error: 'cpu/cycles,cycles/'
                                \___ Failed to find PMU for type 0

Initial error:
event syntax error: 'cpu/cycles,cycles/'
                                \___ Failed to find PMU for type 0
Run 'perf list' for a list of valid events

 Usage: perf stat [<options>] [<command>]

    -e, --event <event>   event selector. use 'perf list' to list available events
```

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/parse-events.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 5dcfbf316bf6..acde097e327c 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1216,6 +1216,14 @@ static int config_term_pmu(struct perf_event_attr *attr,
 	if (term->type_term == PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE) {
 		const struct perf_pmu *pmu = perf_pmus__find_by_type(attr->type);
 
+		if (!pmu) {
+			char *err_str;
+
+			if (asprintf(&err_str, "Failed to find PMU for type %d", attr->type) >= 0)
+				parse_events_error__handle(err, term->err_term,
+							   err_str, /*help=*/NULL);
+			return -EINVAL;
+		}
 		if (perf_pmu__supports_legacy_cache(pmu)) {
 			attr->type = PERF_TYPE_HW_CACHE;
 			return parse_events__decode_legacy_cache(term->config, pmu->type,
-- 
2.41.0.390.g38632f3daf-goog