[PATCH 5/5] perf arm-spe: Reject zero nr_cpu in metadata to prevent division by zero

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

arm_spe__alloc_metadata() reads nr_cpu from the auxtrace_info priv
array without validation.  When a crafted perf.data provides nr_cpu=0,
the per_cpu_sz calculation divides by zero:

  per_cpu_sz = (metadata_size - (hdr_sz * sizeof(u64))) / (*nr_cpu);

Reject nr_cpu <= 0 early, before the division.  The caller already
treats NULL return with metadata_ver != 1 as a parse failure.

Fixes: e52abceb4b6c2723 ("perf arm-spe: Dump metadata with version 2")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Leo Yan <leo.yan@xxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/arm-spe.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index 552f063f126e6769..401aab529309cbd6 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -1605,6 +1605,10 @@ static u64 **arm_spe__alloc_metadata(struct perf_record_auxtrace_info *info,
 	hdr_sz = ptr[ARM_SPE_HEADER_SIZE];
 	*nr_cpu = ptr[ARM_SPE_CPUS_NUM];
 
+	/* nr_cpu is used as a divisor below */
+	if (*nr_cpu <= 0)
+		return NULL;
+
 	metadata = calloc(*nr_cpu, sizeof(*metadata));
 	if (!metadata)
 		return NULL;
-- 
2.55.0