linux-kernel - [PATCH v3 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc

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Date: Fri,  2 Feb 2024 15:40:51 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@....com>, 
	Leo Yan <leo.yan@...aro.org>, John Garry <john.g.garry@...cle.com>, 
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Darren Hart <dvhart@...radead.org>, 
	Davidlohr Bueso <dave@...olabs.net>, 
	"André Almeida" <andrealmeid@...lia.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	K Prateek Nayak <kprateek.nayak@....com>, Sean Christopherson <seanjc@...gle.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Kajol Jain <kjain@...ux.ibm.com>, 
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, Andrew Jones <ajones@...tanamicro.com>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, Atish Patra <atishp@...osinc.com>, 
	"Steinar H. Gunderson" <sesse@...gle.com>, Yang Jihong <yangjihong1@...wei.com>, 
	Yang Li <yang.lee@...ux.alibaba.com>, Changbin Du <changbin.du@...wei.com>, 
	Sandipan Das <sandipan.das@....com>, Ravi Bangoria <ravi.bangoria@....com>, 
	Paran Lee <p4ranlee@...il.com>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Huacai Chen <chenhuacai@...nel.org>, Yanteng Si <siyanteng@...ngson.cn>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
	bpf@...r.kernel.org
Subject: [PATCH v3 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc

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@....com>
Closes: https://lore.kernel.org/lkml/2cd09e7c-eb88-6726-6169-647dcd0a8101@arm.com/
Signed-off-by: Ian Rogers <irogers@...gle.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);
-- 
2.43.0.594.gd9cf4e227d-goog