linux-kernel - Re: usb: mon: freeing active timer

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Date:	Thu, 24 Apr 2014 15:35:27 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Greg KH <greg@...ah.com>
CC:	linux-usb@...r.kernel.org, Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: usb: mon: freeing active timer

On 04/24/2014 03:24 PM, Greg KH wrote:
> On Thu, Apr 24, 2014 at 01:40:14PM -0400, 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:
>> > 
>> > [ 1361.390880] WARNING: CPU: 10 PID: 24274 at lib/debugobjects.c:260 debug_print_object+0x8c/0xb0()
>> > [ 1361.391203] ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x20
>> > [ 1361.391203] Modules linked in:
>> > [ 1361.391203] CPU: 10 PID: 24274 Comm: trinity-c83 Not tainted 3.15.0-rc2-next-20140423-sasha-00018-gc4ff6c4 #408
>> > [ 1361.391203]  0000000000000009 ffff8801de341c78 ffffffffb85271f2 0000000000000001
>> > [ 1361.391203]  ffff8801de341cc8 ffff8801de341cb8 ffffffffb515afcc ffff8801eb3ebd98
>> > [ 1361.391203]  ffff8801eb751870 ffffffffb9e76200 ffffffffb98dc502 ffffffffbc702550
>> > [ 1361.391203] Call Trace:
>> > [ 1361.391203] dump_stack (lib/dump_stack.c:52)
>> > [ 1361.391203] warn_slowpath_common (kernel/panic.c:430)
>> > [ 1361.391203] warn_slowpath_fmt (kernel/panic.c:445)
>> > [ 1361.391203] debug_print_object (lib/debugobjects.c:262)
>> > [ 1361.391203] ? __queue_work (kernel/workqueue.c:1452)
>> > [ 1361.391203] __debug_check_no_obj_freed (lib/debugobjects.c:697)
>> > [ 1361.391203] debug_check_no_obj_freed (lib/debugobjects.c:726)
>> > [ 1361.391203] kmem_cache_free (mm/slub.c:2689 mm/slub.c:2717)
>> > [ 1361.391203] ? kmem_cache_destroy (mm/slab_common.c:363)
>> > [ 1361.391203] kmem_cache_destroy (mm/slab_common.c:363)
>> > [ 1361.391203] mon_text_release (drivers/usb/mon/mon_text.c:643)
>> > [ 1361.391203] __fput (fs/file_table.c:217)
>> > [ 1361.391203] ____fput (fs/file_table.c:253)
>> > [ 1361.391203] task_work_run (kernel/task_work.c:125 (discriminator 1))
>> > [ 1361.391203] do_notify_resume (include/linux/tracehook.h:196 arch/x86/kernel/signal.c:751)
>> > [ 1361.391203] int_signal (arch/x86/kernel/entry_64.S:807)
> So you were running usbmon at the time?  Were you actually monitoring a
> specific USB device/bus, or something else?

This was inside a vm with no actual physical USB devices:

# lsusb -t
lsusb: cannot open "/var/lib/usbutils/usb.ids", No such file or directory
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ozwpan/8p, 12M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dummy_hcd/1p, 480M
    |__ Port 1: Dev 2, If 0, Class=comm., Driver=cdc_eem, 480M

Since it happened while I was fuzzing, I'm not sure what exactly was getting
monitored at that point.


Thanks,
Sasha
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