linux-kernel - Re: [PATCH 1/2] perf ioctl: Add check for the sample

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Date:   Mon, 13 May 2019 10:56:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     jolsa@...hat.com, mpe@...erman.id.au, maddy@...ux.vnet.ibm.com,
        acme@...nel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] perf ioctl: Add check for the sample_period value

On Mon, May 13, 2019 at 09:42:13AM +0200, Peter Zijlstra wrote:
> On Sat, May 11, 2019 at 08:12:16AM +0530, Ravi Bangoria wrote:
> > Add a check for sample_period value sent from userspace. Negative
> > value does not make sense. And in powerpc arch code this could cause
> > a recursive PMI leading to a hang (reported when running perf-fuzzer).
> > 
> > Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> > ---
> >  kernel/events/core.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index abbd4b3b96c2..e44c90378940 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5005,6 +5005,9 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
> >  	if (perf_event_check_period(event, value))
> >  		return -EINVAL;
> >  
> > +	if (!event->attr.freq && (value & (1ULL << 63)))
> > +		return -EINVAL;
> 
> Well, perf_event_attr::sample_period is __u64. Would not be the site
> using it as signed be the one in error?

You forgot to mention commit: 0819b2e30ccb9, so I guess this just makes
it consistent and is fine.