linux-kernel - Re: [PATCH v1 1/2] perf maps: Avoid RC

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Message-ID: <fe28fdc7-7c5c-420f-ac5c-903438d4d62b@linaro.org>
Date: Wed, 19 Nov 2025 12:33:29 +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>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 German Gomez <german.gomez@....com>, Ravi Bangoria <ravi.bangoria@....com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Chun-Tse Shao <ctshao@...gle.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH v1 1/2] perf maps: Avoid RC_CHK use after free



On 19/11/2025 5:05 am, Ian Rogers wrote:
> The case of __maps__fixup_overlap_and_insert where the "new" maps
> covers existing mappings can create a use-after-free with reference
> count checking enabled. The issue is that "pos" holds a map pointer
> from maps_by_address that is put from maps_by_address but then used to
> look for a map in maps_by_name (the compared map is now a
> use-after-free). The issue stems from using maps__remove which redoes
> some of the searches already done by __maps__fixup_overlap_and_insert,
> so optimize the code (by avoiding repeated searches) and avoid the
> use-after-free by inlining the appropriate removal code.
> 
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202511141407.f9edcfa6-lkp@intel.com
> Signed-off-by: Ian Rogers <irogers@...gle.com>

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

> ---
>   tools/perf/util/maps.c | 22 ++++++++++++++++++++--
>   1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
> index 779f6230130a..c321d4f4d846 100644
> --- a/tools/perf/util/maps.c
> +++ b/tools/perf/util/maps.c
> @@ -931,8 +931,9 @@ static int __maps__fixup_overlap_and_insert(struct maps *maps, struct map *new)
>   			return err;
>   		} else {
>   			struct map *next = NULL;
> +			unsigned int nr_maps = maps__nr_maps(maps);
>   
> -			if (i + 1 < maps__nr_maps(maps))
> +			if (i + 1 < nr_maps)
>   				next = maps_by_address[i + 1];
>   
>   			if (!next  || map__start(next) >= map__end(new)) {
> @@ -953,7 +954,24 @@ static int __maps__fixup_overlap_and_insert(struct maps *maps, struct map *new)
>   				check_invariants(maps);
>   				return err;
>   			}
> -			__maps__remove(maps, pos);
> +			/*
> +			 * pos fully covers the previous mapping so remove
> +			 * it. The following is an inlined version of
> +			 * maps__remove that reuses the already computed
> +			 * indices.
> +			 */
> +			map__put(maps_by_address[i]);
> +			memmove(&maps_by_address[i],
> +				&maps_by_address[i + 1],
> +				(nr_maps - i - 1) * sizeof(*maps_by_address));
> +
> +			if (maps_by_name) {
> +				map__put(maps_by_name[ni]);
> +				memmove(&maps_by_name[ni],
> +					&maps_by_name[ni + 1],
> +					(nr_maps - ni - 1) *  sizeof(*maps_by_name));
> +			}
> +			--RC_CHK_ACCESS(maps)->nr_maps;
>   			check_invariants(maps);
>   			/*
>   			 * Maps are ordered but no need to increase `i` as the