linux-kernel - Re: [perf] more perf_fuzzer memory corruption

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Message-ID: <alpine.DEB.2.02.1405011522060.6261@ionos.tec.linutronix.de>
Date:	Thu, 1 May 2014 15:29:19 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [perf] more perf_fuzzer memory corruption

On Thu, 1 May 2014, Thomas Gleixner wrote:

> On Thu, 1 May 2014, Peter Zijlstra wrote:
> > On Thu, May 01, 2014 at 12:26:02PM +0200, Peter Zijlstra wrote:
> > > On Thu, May 01, 2014 at 12:51:33AM +0200, Thomas Gleixner wrote:
> > > > And that's the issue which puzzles us. Let's look at what we expect:
> > > > 
> > > > Now the trace shows a different story:
> > > > 
> > > >      perf_fuzzer-4387  [001]  1802.628659: sys_enter:            NR 298 (69bb58, 0, ffffffff, 12, 0, 0)
> > > 
> > > That's a per-cpu event (.pid = -1, .cpu = 12), they don't get inherited,
> > > so the only thing keeping it alive is the fd the child got. So
> > > exit_files() killing this thing makes perfect sense.
> 
> Duh, right. Should have noticed :(

And having a second look:

SYSCALL_DEFINE5(perf_event_open,
		struct perf_event_attr __user *, attr_uptr,
		pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)

sys_enter:            NR 298 (69bb58, 0, ffffffff, 12, 0, 0)

attr_uptr = 0x69bb58
pid 	  = 0
cpu 	  = -1
group_fd  = 12
flags 	  = 0

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