linux-kernel - Re: [PATCHv5] perf tool: fix dereferencing NULL al->maps

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Message-ID: <ZqOtkPGcijWW52aj@x1>
Date: Fri, 26 Jul 2024 11:07:12 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>, Casey Chen <cachen@...estorage.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	irogers@...gle.com, yzhong@...estorage.com
Subject: Re: [PATCHv5] perf tool: fix dereferencing NULL al->maps

On Mon, Jul 22, 2024 at 03:15:48PM -0600, Casey Chen wrote:
> With 0dd5041c9a0e ("perf addr_location: Add init/exit/copy functions"),
> when cpumode is 3 (macro PERF_RECORD_MISC_HYPERVISOR),
> thread__find_map() could return with al->maps being NULL.
> 
> The path below could add a callchain_cursor_node with NULL ms.maps.
> 
> add_callchain_ip()
>   thread__find_symbol(.., &al)
>     thread__find_map(.., &al)   // al->maps becomes NULL
>   ms.maps = maps__get(al.maps)
>   callchain_cursor_append(..., &ms, ...)
>     node->ms.maps = maps__get(ms->maps)
> 
> Then the path below would dereference NULL maps and get segfault.
> 
> fill_callchain_info()
>   maps__machine(node->ms.maps);
> 
> Fix it by checking if maps is NULL in fill_callchain_info().
> 
> Signed-off-by: Casey Chen <cachen@...estorage.com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>

Reviewed-by: Arnaldo Carvalho de Melo <acme@...hat.com>

- Arnaldo

> ---
>  tools/perf/util/callchain.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 1730b852a947..6d075648d2cc 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -1141,7 +1141,7 @@ int hist_entry__append_callchain(struct hist_entry *he, struct perf_sample *samp
>  int fill_callchain_info(struct addr_location *al, struct callchain_cursor_node *node,
>  			bool hide_unresolved)
>  {
> -	struct machine *machine = maps__machine(node->ms.maps);
> +	struct machine *machine = node->ms.maps ? maps__machine(node->ms.maps) : NULL;
>  
>  	maps__put(al->maps);
>  	al->maps = maps__get(node->ms.maps);
> -- 
> 2.45.2
>