linux-kernel - Re: [perf] yet another 32/64-bit range check failure

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Message-ID: <20140423101038.GK11096@twins.programming.kicks-ass.net>
Date:	Wed, 23 Apr 2014 12:10:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [perf] yet another 32/64-bit range check failure

On Wed, Apr 23, 2014 at 12:14:52AM -0400, Vince Weaver wrote:
> On Tue, 22 Apr 2014, Vince Weaver wrote:
> 
> > This is allowing events to be allocated memory but not being freed somehow
> > before returning EINVAL (a memory leak).
> > At least it looks like this is happening in the huge traces I have trying 
> > to track down the perf_fuzzer memory corruption bug.
> 
> I can't find where the memory leak happens, but it looks like this in the 
> trace:
> 
> [ 3524.626452] perf_fuz-1798    0.... 1271584315us : sys_enter: NR 298 (698e40, 706, ffffffff, f, 800000000000, 800000000000)
> [ 3524.642312] perf_fuz-1798    0.... 1271584324us : kmalloc: call_site=ffffffff8113a575 ptr=ffff88007d5b0800 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> [ 3524.662598] perf_fuz-1798    0.... 1271584337us : sys_exit: NR 298 = -22
> 
> The call site for the kmalloc is in perf_event_alloc()
> 
> The memory is eventually freed as:
> 
> [ 3547.895534]   <idle>-0       0.Ns. 1271595088us : kfree: call_site=ffffffff811316aa ptr=ffff88007d5b0800

So perf_event_open() -> err_alloc: -> free_event() -> __free_event() ->
call_rcu() -> free_event_rcu() -> kfree().

Would explain that, right? The memory is RCU freed, which means we need
to wait a grace period before releasing it.
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