perf sched: Bounds-check prio before test_bit() in timehist

timehist_skip_sample() reads prio from untrusted tracepoint data via
perf_sample__intval(sample, "prev_prio") without bounds validation.
A crafted perf.data with prev_prio >= MAX_PRIO (140) causes test_bit()
to read past the end of the prio_bitmap, which is only MAX_PRIO bits.

Add a prio >= 0 guard before the test_bit() call and skip out-of-range
values (>= MAX_PRIO) that can never match the user's filter set.

The original prio != -1 already let all negatives other than -1 through
(after an undefined-behavior bitmap read); the new prio >= 0 guard
preserves that pass-through behavior — negative means "no priority
info", so the event is shown unfiltered — while fixing the OOB.
Values >= MAX_PRIO are skipped because they cannot be represented in
the filter bitmap.

Fixes: 9b3a48bbe20d9692 ("perf sched timehist: Add --prio option")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Yang Jihong <yangjihong@bytedance.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 1ff01f03d2ad..caf05863a54e 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -2645,7 +2645,9 @@ static bool timehist_skip_sample(struct perf_sched *sched,
 		else if (evsel__name_is(sample->evsel, "sched:sched_switch"))
 			prio = perf_sample__intval(sample, "prev_prio");
 
-		if (prio != -1 && !test_bit(prio, sched->prio_bitmap)) {
+		/* negative prio means no info; out-of-range prio can't match the filter */
+		if (prio >= 0 &&
+		    (prio >= MAX_PRIO || !test_bit(prio, sched->prio_bitmap))) {
 			rc = true;
 			sched->skipped_samples++;
 		}