[PATCH 6.12 142/567] libperf cpumap: Fix perf_cpu_map__max for an empty/NULL map

Greg Kroah-Hartman
2026-01-06T17:23:52Z

From: Ian Rogers <irogers@google.com>

[ Upstream commit a0a4173631bfcfd3520192c0a61cf911d6a52c3a ]

Passing an empty map to perf_cpu_map__max triggered a SEGV. Explicitly
test for the empty map.

Reported-by: Ingo Molnar <mingo@kernel.org>
Closes: https://lore.kernel.org/linux-perf-users/aSwt7yzFjVJCEmVp@gmail.com/
Tested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/perf/cpumap.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index cae799ad44e1..e5938b91199f 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -409,10 +409,12 @@ struct perf_cpu perf_cpu_map__max(const struct perf_cpu_map *map)
.cpu = -1
};

- // cpu_map__trim_new() qsort()s it, cpu_map__default_new() sorts it as well.
- return __perf_cpu_map__nr(map) > 0
- ? __perf_cpu_map__cpu(map, __perf_cpu_map__nr(map) - 1)
- : result;
+ if (!map)
+ return result;
+
+ // The CPUs are always sorted and nr is always > 0 as 0 length map is
+ // encoded as NULL.
+ return __perf_cpu_map__cpu(map, __perf_cpu_map__nr(map) - 1);
}

/** Is 'b' a subset of 'a'. */
--
2.51.0