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 09:07:04 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	He Kuang <hekuang@...wei.com>, peterz@...radead.org,
	mingo@...hat.com, 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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] perf tools: Fix NULL pointer deference when vdso not
 found

Em Thu, Jun 23, 2016 at 10:02:39AM +0800, Wangnan (F) escreveu:
> 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.

Ok, I removed f9b2bdf228 because of this crash, Ingo reported it, now
that I see this new patch and checked that the crash was introduced by
f9b2bdf228 I'll just combine those two and test again using a 32-bit
hackbench on top of f9b2bdf228, to reproduce the crash, then on top of
both patches combined.

- Arnaldo
 
> 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;
>