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Subject: Re: [PATCH 5/5] perf tools: Fix NULL pointer deference when vdso not
 found
To: He Kuang <hekuang@huawei.com>, <peterz@infradead.org>, <mingo@redhat.com>,
        <acme@kernel.org>, <alexander.shishkin@linux.intel.com>,
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        <tumanova@linux.vnet.ibm.com>, <kan.liang@intel.com>,
        <penberg@kernel.org>, <dsahern@gmail.com>
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 <1466578626-92406-6-git-send-email-hekuang@huawei.com>
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From: "Wangnan (F)" <wangnan0@huawei.com>
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Date: Thu, 23 Jun 2016 10:02:39 +0800
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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@huawei.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;