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

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Message-ID: <20190513074213.GH2623@hirez.programming.kicks-ass.net>
Date:   Mon, 13 May 2019 09:42:13 +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 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?