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 10:28:42 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	"Wangnan (F)" <wangnan0@...wei.com>, 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 09:07:04AM -0300, Arnaldo Carvalho de Melo escreveu:
> 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.

Tested, reproduced, ammended, fixed, applied, thanks!

- Arnaldo
 
> - 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;
> >