linux-kernel - Re: [PATCH v1] perf test cpumap: Avoid use-after-free following merge

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Message-ID: <ac163e57-1bf8-4662-920c-9dbfecb26c06@linaro.org>
Date: Wed, 8 Jan 2025 15:07:53 +0000
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Leo Yan <leo.yan@....com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf test cpumap: Avoid use-after-free following merge



On 08/01/2025 5:15 am, Ian Rogers wrote:
> Previously cpu maps in the test weren't modified by calls to the cpu
> map API, however, perf_cpu_map__merge was modified so the left hand
> argument was updated. In the test this meant the maps copy of the
> "two" map was put/deleted in the merge meaning when accessed via maps,
> the pointer was stale and to the put/deleted memory. To fix this add
> an extra layer of indirection to the maps array, so the updated value
> of two is accessed.
> 
> Fixes: a9d2217556f7 ("libperf cpumap: Refactor perf_cpu_map__merge()")
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Reviewed-by: James Clark <james.clark@...aro.org>

> ---
>   tools/perf/tests/cpumap.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/tests/cpumap.c b/tools/perf/tests/cpumap.c
> index 5ed7ff072ea3..2354246afc5a 100644
> --- a/tools/perf/tests/cpumap.c
> +++ b/tools/perf/tests/cpumap.c
> @@ -252,16 +252,16 @@ static int test__cpu_map_equal(struct test_suite *test __maybe_unused, int subte
>   	struct perf_cpu_map *empty = perf_cpu_map__intersect(one, two);
>   	struct perf_cpu_map *pair = perf_cpu_map__new("1-2");
>   	struct perf_cpu_map *tmp;
> -	struct perf_cpu_map *maps[] = {empty, any, one, two, pair};
> +	struct perf_cpu_map **maps[] = {&empty, &any, &one, &two, &pair};
>   
>   	for (size_t i = 0; i < ARRAY_SIZE(maps); i++) {
>   		/* Maps equal themself. */
> -		TEST_ASSERT_VAL("equal", perf_cpu_map__equal(maps[i], maps[i]));
> +		TEST_ASSERT_VAL("equal", perf_cpu_map__equal(*maps[i], *maps[i]));
>   		for (size_t j = 0; j < ARRAY_SIZE(maps); j++) {
>   			/* Maps dont't equal each other. */
>   			if (i == j)
>   				continue;
> -			TEST_ASSERT_VAL("not equal", !perf_cpu_map__equal(maps[i], maps[j]));
> +			TEST_ASSERT_VAL("not equal", !perf_cpu_map__equal(*maps[i], *maps[j]));
>   		}
>   	}
>   
> @@ -274,7 +274,7 @@ static int test__cpu_map_equal(struct test_suite *test __maybe_unused, int subte
>   	perf_cpu_map__put(tmp);
>   
>   	for (size_t i = 0; i < ARRAY_SIZE(maps); i++)
> -		perf_cpu_map__put(maps[i]);
> +		perf_cpu_map__put(*maps[i]);
>   
>   	return TEST_OK;
>   }