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

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Message-ID: <CALCePG0GtG4DQwzJ-QCJRScfxVg3Up6Xeemxh48qSf2VjxjebA@mail.gmail.com>
Date: Tue, 23 Jul 2024 18:01:38 -0700
From: Casey Chen <cachen@...estorage.com>
To: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	namhyung@...nel.org, irogers@...gle.com
Cc: yzhong@...estorage.com
Subject: Re: [PATCHv5] perf tool: fix dereferencing NULL al->maps

Ian / Namhyung,

Could you take a look at the latest diff PATCHv5 ?

Thanks,
Casey

On Mon, Jul 22, 2024 at 2:15 PM Casey Chen <cachen@...estorage.com> 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>
> ---
>  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
>