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Date:	Mon, 28 Jul 2014 19:04:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Ingo Molnar <mingo@...nel.org>, acme@...stprotocols.net,
	Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf: invalid memory access in perf_swevent_del

On Fri, Jul 25, 2014 at 10:34:11PM -0400, Sasha Levin wrote:
> On 05/10/2014 07:34 PM, Sasha Levin wrote:
> > Hi all,
> > 
> > While fuzzing with trinity inside a KVM tools guest running the latest -next
> > kernel I've stumbled on the following spew:
> 
> Ping? I'm still seeing corruption on perf_swevent_del and perf_swevent_init:
> 
> [  488.092839] AddressSanitizer: use after free in perf_swevent_del+0x33/0x70 at addr ffff8805f430ea48

> [  488.100020] Call Trace:
> [  488.100020] dump_stack (lib/dump_stack.c:52)
> [  488.100020] kasan_report_error (mm/kasan/report.c:98 mm/kasan/report.c:166)
> [  488.100020] __asan_store8 (mm/kasan/kasan.c:400)
> [  488.100020] perf_swevent_del (include/linux/list.h:618 include/linux/rculist.h:345 kernel/events/core.c:5758)
> [  488.100020] event_sched_out.isra.49 (kernel/events/core.c:1416)
> [  488.100020] group_sched_out (kernel/events/core.c:1442)
> [  488.100020] ctx_sched_out (kernel/events/core.c:2185 (discriminator 3))
> [  488.100020] __perf_event_task_sched_out (kernel/events/core.c:2360 kernel/events/core.c:2385)
> [  488.100020] perf_event_task_sched_out (include/linux/perf_event.h:702)

> [  488.100020] Write of size 8 by thread T9306:
> [  488.100020] Memory state around the buggy address:
> [  488.100020]  ffff8805f430e780: fc fc fc fc fc fc fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430e800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430e880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430e900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430e980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020] >ffff8805f430ea00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]                                               ^
> [  488.100020]  ffff8805f430ea80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430eb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430eb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430ec00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  488.100020]  ffff8805f430ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Useful, that kasan doesn't use POISON_FREE... :/

> [  517.616094] =============================================================================
> [  517.619549] BUG kmalloc-4096 (Not tainted): Poison overwritten
> [  517.621321] -----------------------------------------------------------------------------
> [  517.621321]
> [  517.621321] Disabling lock debugging due to kernel taint
> [  517.621321] INFO: 0xffff8805f430ea48-0xffff8805f430eb77. First byte 0x0 instead of 0x6b
> [  517.621321] INFO: Allocated in perf_swevent_init+0x29f/0x440 age=14082 cpu=17 pid=9306
> [  517.621321]  __slab_alloc+0x65e/0x740
> [  517.621321]  kmem_cache_alloc_trace+0x17c/0x3a0
> [  517.621321]  perf_swevent_init+0x29f/0x440
> [  517.621321]  perf_init_event+0x293/0x340
> [  517.621321]  perf_event_alloc+0x5b8/0x6e0
> [  517.621321]  SYSC_perf_event_open+0x39b/0xf50
> [  517.621321]  SyS_perf_event_open+0x9/0x10
> [  517.621321]  tracesys+0xe1/0xe6

So this would be swevent_hlist_get_cpu()'s swevent_hlist allocation.

> [  517.621321] INFO: Freed in rcu_nocb_kthread+0x911/0x13f0 age=2958 cpu=3 pid=25
> [  517.621321]  __slab_free+0x276/0x3e0
> [  517.621321]  kfree+0x31a/0x390
> [  517.621321]  rcu_nocb_kthread+0x911/0x13f0
> [  517.621321]  kthread+0x144/0x170
> [  517.621321]  ret_from_fork+0x7c/0xb0
> [  517.621321] INFO: Slab 0xffffea0017d0c200 objects=7 used=7 fp=0x          (null) flags=0x6fffff80004080
> [  517.621321] INFO: Object 0xffff8805f430e7b0 @offset=26544 fp=0xffff8805f4308000

And this would be the corresponding free:

  sw_perf_event_destroy()
  swevent_hlist_put()
  swevent_hlist_put_cpu()
  swevent_hlist_release()

Which would suggest a refcounting boo-boo, cute.


Does your trinity do hotplug while creating/destroying events?

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