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

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Message-ID: <20150520160911.GM18673@twins.programming.kicks-ass.net>
Date:	Wed, 20 May 2015 18:09:11 +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 05:26:07PM +0200, Peter Zijlstra wrote:
> Except of course that ->event_init() likes to do an allocation :/
> 
> Needs to be fixed differently.

So this puts the lock in the x86 code, it seems to build and run.

But my brain is fried after staring at this pmu scheduling code all day,
so maybe its wrong again.

Stephane, can you have a look?

---
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 87848eb..344bb90 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1823,6 +1823,9 @@ static int validate_group(struct perf_event *event)
 	fake_cpuc = allocate_fake_cpuc();
 	if (IS_ERR(fake_cpuc))
 		return PTR_ERR(fake_cpuc);
+
+
+	raw_spin_lock_irq(&leader->ctx->lock);
 	/*
 	 * the event is not yet connected with its
 	 * siblings therefore we must first collect
@@ -1843,6 +1846,8 @@ static int validate_group(struct perf_event *event)
 	ret = x86_pmu.schedule_events(fake_cpuc, n, NULL);
 
 out:
+	raw_spin_unlock_irq(&leader->ctx->lock);
+
 	free_fake_cpuc(fake_cpuc);
 	return ret;
 }
--
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