linux-kernel - [PATCH v2] perf stat-display: Check if snprintf()'s fmt argument is NULL

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Message-ID: <01CA7674B690CA24+20230804020907.144562-2-ye@kaige.org>
Date:   Fri,  4 Aug 2023 10:09:08 +0800
From:   Kaige Ye <ye@...ge.org>
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
        adrian.hunter@...el.com
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kaige Ye <ye@...ge.org>
Subject: [PATCH v2] perf stat-display: Check if snprintf()'s fmt argument is NULL

It is undefined behavior to pass NULL as snprintf()'s fmt argument.
Here is an example to trigger the problem:

  $ perf stat --metric-only -x, -e instructions -- sleep 1
  insn per cycle,
  Segmentation fault (core dumped)

With this patch:

  $ perf stat --metric-only -x, -e instructions -- sleep 1
  insn per cycle,
  ,

Signed-off-by: Kaige Ye <ye@...ge.org>
---
V1 -> V2: Addressed Ian's comments (Ian Rogers)
---
 tools/perf/util/stat-display.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index 7329b3340..031888545 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -578,7 +578,7 @@ static void print_metric_only_csv(struct perf_stat_config *config __maybe_unused
 	if (!valid_only_metric(unit))
 		return;
 	unit = fixunit(tbuf, os->evsel, unit);
-	snprintf(buf, sizeof buf, fmt, val);
+	snprintf(buf, sizeof(buf), fmt ?: "", val);
 	ends = vals = skip_spaces(buf);
 	while (isdigit(*ends) || *ends == '.')
 		ends++;
@@ -600,7 +600,7 @@ static void print_metric_only_json(struct perf_stat_config *config __maybe_unuse
 	if (!valid_only_metric(unit))
 		return;
 	unit = fixunit(tbuf, os->evsel, unit);
-	snprintf(buf, sizeof(buf), fmt, val);
+	snprintf(buf, sizeof(buf), fmt ?: "", val);
 	ends = vals = skip_spaces(buf);
 	while (isdigit(*ends) || *ends == '.')
 		ends++;

base-commit: f6b8436bede3e80226e8b2100279c4450c73806a
-- 
2.41.0