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Date: Wed, 31 Jan 2024 20:22:30 -0800
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Subject: [PATCH v2 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc
From: Ian Rogers <irogers@google.com>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, Mark Rutland <mark.rutland@arm.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Namhyung Kim <namhyung@kernel.org>, Ian Rogers <irogers@google.com>, 
	Adrian Hunter <adrian.hunter@intel.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, 
	Mike Leach <mike.leach@linaro.org>, James Clark <james.clark@arm.com>, 
	Leo Yan <leo.yan@linaro.org>, John Garry <john.g.garry@oracle.com>, 
	Will Deacon <will@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Darren Hart <dvhart@infradead.org>, 
	Davidlohr Bueso <dave@stgolabs.net>, 
	"=?UTF-8?q?Andr=C3=A9=20Almeida?=" <andrealmeid@igalia.com>, Kan Liang <kan.liang@linux.intel.com>, 
	K Prateek Nayak <kprateek.nayak@amd.com>, Sean Christopherson <seanjc@google.com>, 
	Paolo Bonzini <pbonzini@redhat.com>, Kajol Jain <kjain@linux.ibm.com>, 
	Athira Rajeev <atrajeev@linux.vnet.ibm.com>, Andrew Jones <ajones@ventanamicro.com>, 
	Alexandre Ghiti <alexghiti@rivosinc.com>, Atish Patra <atishp@rivosinc.com>, 
	"Steinar H. Gunderson" <sesse@google.com>, Yang Jihong <yangjihong1@huawei.com>, 
	Yang Li <yang.lee@linux.alibaba.com>, Changbin Du <changbin.du@huawei.com>, 
	Sandipan Das <sandipan.das@amd.com>, Ravi Bangoria <ravi.bangoria@amd.com>, 
	Paran Lee <p4ranlee@gmail.com>, Nick Desaulniers <ndesaulniers@google.com>, 
	Huacai Chen <chenhuacai@kernel.org>, Yanteng Si <siyanteng@loongson.cn>, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
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Potential corner cases could cause a cpumap to be allocated with size
0, but an empty cpumap should be represented as NULL. Add a path in
perf_cpu_map__alloc to ensure this.

Suggested-by: James Clark <james.clark@arm.com>
Closes: https://lore.kernel.org/lkml/2cd09e7c-eb88-6726-6169-647dcd0a8101@arm.com/
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/cpumap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index ba49552952c5..cae799ad44e1 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -18,9 +18,13 @@ void perf_cpu_map__set_nr(struct perf_cpu_map *map, int nr_cpus)
 
 struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
 {
-	RC_STRUCT(perf_cpu_map) *cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
+	RC_STRUCT(perf_cpu_map) *cpus;
 	struct perf_cpu_map *result;
 
+	if (nr_cpus == 0)
+		return NULL;
+
+	cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
 	if (ADD_RC_CHK(result, cpus)) {
 		cpus->nr = nr_cpus;
 		refcount_set(&cpus->refcnt, 1);
-- 
2.43.0.429.g432eaa2c6b-goog