linux-kernel - Re: perf: fuzzer triggers NULL pointer derefreence in x86_schedule

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Message-ID: <20150520152607.GK18673@twins.programming.kicks-ass.net>
Date:	Wed, 20 May 2015 17:26:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: perf: fuzzer triggers NULL pointer derefreence in
 x86_schedule_events

On Wed, May 20, 2015 at 03:49:22PM +0200, Peter Zijlstra wrote:
> ---
>  kernel/events/core.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 1a3bf48..a4f93fb 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7391,13 +7391,16 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
>  		ctx = perf_event_ctx_lock_nested(event->group_leader,
>  						 SINGLE_DEPTH_NESTING);
>  		BUG_ON(!ctx);
> +		raw_spin_lock_irq(&ctx->lock);
>  	}
>  
>  	event->pmu = pmu;
>  	ret = pmu->event_init(event);
>  
> -	if (ctx)
> +	if (ctx) {
> +		raw_spin_unlock_irq(&ctx->lock);
>  		perf_event_ctx_unlock(event->group_leader, ctx);
> +	}
>  
>  	if (ret)
>  		module_put(pmu->module);

Except of course that ->event_init() likes to do an allocation :/

Needs to be fixed differently.
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