[PATCH] perf pmus: Fix duplicate events caused segfault

[Eric Lin]

Currently, if vendor JSON files have two duplicate event names,
the "perf list" command will trigger a segfault.

In commit e6ff1eed3584 ("perf pmu: Lazily add JSON events"),
pmu_events_table__num_events() gets the number of JSON events
from table_pmu->num_entries, which includes duplicate events
if there are duplicate event names in the JSON files.

perf_pmu__for_each_event() adds JSON events to the pmu->alias
list and copies sevent data to the aliases array. However, the
pmu->alias list does not contain duplicate events, as
perf_pmu__new_alias() checks if the name was already created.

When sorting the alias data, if there are two duplicate events,
it causes a segfault in cmp_sevent() due to invalid aliases in
the aliases array.

To avoid such segfault caused by duplicate event names in the
JSON files, the len should be updated before sorting the aliases.

Fixes: e6ff1eed3584 ("perf pmu: Lazily add JSON events")
Signed-off-by: Eric Lin <eric.lin@xxxxxxxxxx>
---
 tools/perf/util/pmus.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index b9b4c5eb5002..e38c3fd4d1ff 100644
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -443,7 +443,7 @@ void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *p
 {
 	struct perf_pmu *pmu;
 	int printed = 0;
-	int len;
+	size_t len, j;
 	struct sevent *aliases;
 	struct events_callback_state state;
 	bool skip_duplicate_pmus = print_cb->skip_duplicate_pmus(print_state);
@@ -474,8 +474,9 @@ void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *p
 		perf_pmu__for_each_event(pmu, skip_duplicate_pmus, &state,
 					 perf_pmus__print_pmu_events__callback);
 	}
+	len = state.index;
 	qsort(aliases, len, sizeof(struct sevent), cmp_sevent);
-	for (int j = 0; j < len; j++) {
+	for (j = 0; j < len; j++) {
 		/* Skip duplicates */
 		if (j > 0 && pmu_alias_is_duplicate(&aliases[j], &aliases[j - 1]))
 			continue;
-- 
2.43.2