linux-kernel - Re: [PATCH 5/5] perf tools: Fix NULL pointer deference when vdso not found

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Date:	Thu, 23 Jun 2016 10:02:39 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	He Kuang <hekuang@...wei.com>, <peterz@...radead.org>,
	<mingo@...hat.com>, <acme@...nel.org>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...hat.com>,
	<jpoimboe@...hat.com>, <ak@...ux.intel.com>, <eranian@...gle.com>,
	<namhyung@...nel.org>, <adrian.hunter@...el.com>,
	<sukadev@...ux.vnet.ibm.com>, <masami.hiramatsu.pt@...achi.com>,
	<tumanova@...ux.vnet.ibm.com>, <kan.liang@...el.com>,
	<penberg@...nel.org>, <dsahern@...il.com>
CC:	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] perf tools: Fix NULL pointer deference when vdso not
 found

Hi,

This patch fixes a real crash problem when we do 'perf report'
on an arm64 platform with arm32 program.
It is introduced by commit f9b2bdf228 ("perf tools: Find vdso
with the consider of cross-platform"). From dmesg report, perf
crashes in dso__type() because dso is NULL.

Still don't know why on x86 it never crash, but it is obviously
that we need to check the return vaule from __dso__find(): it can
be NULL.

So please consider pulling.

Thank you.

On 2016/6/22 14:57, He Kuang wrote:
> We should check if 'dso' is a null pointer before passing it to the
> function dso__type(), otherwise a segfault will be raised in
> dso__data_get_fd(). In function machine__find_vdso(), the return value
> checking of 'dso' is missed and this patch fixes this issue.
>
> Signed-off-by: He Kuang <hekuang@...wei.com>
> ---
>   tools/perf/util/vdso.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/vdso.c b/tools/perf/util/vdso.c
> index 8f81c41..7bdcad4 100644
> --- a/tools/perf/util/vdso.c
> +++ b/tools/perf/util/vdso.c
> @@ -296,7 +296,7 @@ static struct dso *machine__find_vdso(struct machine *machine,
>   		if (!dso) {
>   			dso = __dsos__find(&machine->dsos, DSO__NAME_VDSO,
>   					   true);
> -			if (dso_type != dso__type(dso, machine))
> +			if (dso && dso_type != dso__type(dso, machine))
>   				dso = NULL;
>   		}
>   		break;