[PATCH 14/23] perf hwmon: Guard label read against empty or failed reads

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

hwmon_pmu__read_events() reads label files with read() into a stack
buffer, strips trailing newlines, then checks buf[0] == '\0'.  When
read() returns 0 (empty file) or -1 (error), the buffer is never
written, so buf[0] reads uninitialized stack memory.  If the garbage
byte is non-zero, the code falls through to strdup(buf) which copies
arbitrary stack data as the label string.

Fix by checking read_len <= 0 before accessing buf contents, closing
the fd and skipping the entry.

Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Fixes: 53cc0b351ec99278 ("perf hwmon_pmu: Add a tool PMU exposing events from hwmon in sysfs")
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/hwmon_pmu.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/hwmon_pmu.c b/tools/perf/util/hwmon_pmu.c
index bdcbe887579a1f08..efd3067a2e591050 100644
--- a/tools/perf/util/hwmon_pmu.c
+++ b/tools/perf/util/hwmon_pmu.c
@@ -295,8 +295,11 @@ static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 			while (read_len > 0 && buf[read_len - 1] == '\n')
 				read_len--;
 
-			if (read_len > 0)
-				buf[read_len] = '\0';
+			if (read_len <= 0) {
+				close(fd);
+				continue;
+			}
+			buf[read_len] = '\0';
 
 			if (buf[0] == '\0') {
 				pr_debug("hwmon_pmu: empty label file %s %s\n",
-- 
2.54.0