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Date: Wed, 7 Oct 2020 09:48:04 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Shuah Khan <shuah@...nel.org>,
Valentina Manea <valentina.manea.m@...il.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
LKML <linux-kernel@...r.kernel.org>,
USB list <linux-usb@...r.kernel.org>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
syzbot <syzbot+bf1a360e305ee719e364@...kaller.appspotmail.com>,
Nazime Hande Harputluoglu <handeharputlu@...gle.com>,
Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: KASAN: null-ptr-deref Write in event_handler
On 10/7/20 8:28 AM, Andrey Konovalov wrote:
> On Wed, Oct 7, 2020 at 3:56 PM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>
>> On 10/5/20 2:44 PM, Shuah Khan wrote:
>>> On 10/5/20 8:04 AM, Andrey Konovalov wrote:
>>>> On Mon, Oct 5, 2020 at 3:59 PM syzbot
>>>> <syzbot+bf1a360e305ee719e364@...kaller.appspotmail.com> wrote:
>>>>>
>>>>> Hello,
>>>>>
>>>>> syzbot found the following issue on:
>>>>>
>>>>> HEAD commit: d3d45f82 Merge tag 'pinctrl-v5.9-2' of
>>>>> git://git.kernel.or..
>>>>> git tree: upstream
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15781d8f900000
>>>>> kernel config:
>>>>> https://syzkaller.appspot.com/x/.config?x=89ab6a0c48f30b49
>>>>> dashboard link:
>>>>> https://syzkaller.appspot.com/bug?extid=bf1a360e305ee719e364
>>>>> compiler: gcc (GCC) 10.1.0-syz 20200507
>>>>> syz repro:
>>>>> https://syzkaller.appspot.com/x/repro.syz?x=16cbaa7d900000
>>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1364f367900000
>>>>>
>>>>> IMPORTANT: if you fix the issue, please add the following tag to the
>>>>> commit:
>>>>> Reported-by: syzbot+bf1a360e305ee719e364@...kaller.appspotmail.com
>>>>>
>>>>> vhci_hcd: stop threads
>>>>> vhci_hcd: release socket
>>>>> vhci_hcd: disconnect device
>>>>> ==================================================================
>>>>> BUG: KASAN: null-ptr-deref in instrument_atomic_write
>>>>> include/linux/instrumented.h:71 [inline]
>>>>> BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed
>>>>> include/asm-generic/atomic-instrumented.h:142 [inline]
>>>>> BUG: KASAN: null-ptr-deref in refcount_add
>>>>> include/linux/refcount.h:201 [inline]
>>>>> BUG: KASAN: null-ptr-deref in refcount_inc
>>>>> include/linux/refcount.h:241 [inline]
>>>>> BUG: KASAN: null-ptr-deref in get_task_struct
>>>>> include/linux/sched/task.h:104 [inline]
>>>>> BUG: KASAN: null-ptr-deref in kthread_stop+0x90/0x7e0
>>>>> kernel/kthread.c:591
>>>>> Write of size 4 at addr 000000000000001c by task kworker/u4:5/2519
>>>>>
>>>>> CPU: 1 PID: 2519 Comm: kworker/u4:5 Not tainted 5.9.0-rc7-syzkaller #0
>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>>>> BIOS Google 01/01/2011
>>>>> Workqueue: usbip_event event_handler
>>>>> Call Trace:
>>>>> __dump_stack lib/dump_stack.c:77 [inline]
>>>>> dump_stack+0x198/0x1fd lib/dump_stack.c:118
>>>>> __kasan_report mm/kasan/report.c:517 [inline]
>>>>> kasan_report.cold+0x5/0x37 mm/kasan/report.c:530
>>>>> check_memory_region_inline mm/kasan/generic.c:186 [inline]
>>>>> check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
>>>>> instrument_atomic_write include/linux/instrumented.h:71 [inline]
>>>>> atomic_fetch_add_relaxed
>>>>> include/asm-generic/atomic-instrumented.h:142 [inline]
>>>>> refcount_add include/linux/refcount.h:201 [inline]
>>>>> refcount_inc include/linux/refcount.h:241 [inline]
>>>>> get_task_struct include/linux/sched/task.h:104 [inline]
>>>>> kthread_stop+0x90/0x7e0 kernel/kthread.c:591
>>>>> vhci_shutdown_connection+0x170/0x2a0 drivers/usb/usbip/vhci_hcd.c:1015
>>>>> event_handler+0x1a5/0x450 drivers/usb/usbip/usbip_event.c:78
>>>>> process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>>>>> worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>>>>> kthread+0x3b5/0x4a0 kernel/kthread.c:292
>>>>> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>>>> ==================================================================
>>>>> Kernel panic - not syncing: panic_on_warn set ...
>>>>> CPU: 1 PID: 2519 Comm: kworker/u4:5 Tainted: G B
>>>>> 5.9.0-rc7-syzkaller #0
>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>>>> BIOS Google 01/01/2011
>>>>> Workqueue: usbip_event event_handler
>>>>> Call Trace:
>>>>> __dump_stack lib/dump_stack.c:77 [inline]
>>>>> dump_stack+0x198/0x1fd lib/dump_stack.c:118
>>>>> panic+0x382/0x7fb kernel/panic.c:231
>>>>> end_report+0x4d/0x53 mm/kasan/report.c:104
>>>>> __kasan_report mm/kasan/report.c:520 [inline]
>>>>> kasan_report.cold+0xd/0x37 mm/kasan/report.c:530
>>>>> check_memory_region_inline mm/kasan/generic.c:186 [inline]
>>>>> check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
>>>>> instrument_atomic_write include/linux/instrumented.h:71 [inline]
>>>>> atomic_fetch_add_relaxed
>>>>> include/asm-generic/atomic-instrumented.h:142 [inline]
>>>>> refcount_add include/linux/refcount.h:201 [inline]
>>>>> refcount_inc include/linux/refcount.h:241 [inline]
>>>>> get_task_struct include/linux/sched/task.h:104 [inline]
>>>>> kthread_stop+0x90/0x7e0 kernel/kthread.c:591
>>>>> vhci_shutdown_connection+0x170/0x2a0 drivers/usb/usbip/vhci_hcd.c:1015
>>>>> event_handler+0x1a5/0x450 drivers/usb/usbip/usbip_event.c:78
>>>>> process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>>>>> worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>>>>> kthread+0x3b5/0x4a0 kernel/kthread.c:292
>>>>> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>>>> Kernel Offset: disabled
>>>>> Rebooting in 86400 seconds..
>>>>
>>>> Hi Valentina and Shuah,
>>>>
>>>> There appears to be a race condition in the USB/IP vhci_hcd shutdown
>>>> procedure. It happens quite often during fuzzing with syzkaller, and
>>>> prevents us from going deeper into the USB/IP code.
>>>>
>>>> Could you advise us what would be the best fix for this?
>>>>
>>>
>>> Hi Andrey,
>>>
>>> Reading the comments for this routine, looks like there is an assumption
>>> that context begins cleanup and race conditions aren't considered.
>>>
>>> The right fix is holding vhci->lock and vdev->priv_lock to protect
>>> critical sections in this routine. I will send a patch for this.
>>>
>>
>> Hi Andrey,
>>
>> I have been unable to reproduce the problem with the reproducer
>> so far. You mentioned it happens quite often.
>>
>> - matched config with yours
>> - load vhci_hcd module and run the reproducer
>
> Hm, if you matched the config, then the module should be built-in?
>
Right. I did notice that your config has built-in. This shouldn't
matter, I have a kernel built with it static. I will try it to
see if it makes a difference.
>>
>> I do see the messages during shutdown - stop threads etc.
>>
>> What am I missing?
>
> This appears to be a race that requires precise timings. I failed to
> reproduce it with the C reproducer, but I managed to reproduce it with
> the syzkaller repro program:
>
> https://syzkaller.appspot.com/x/repro.syz?x=16cbaa7d900000
>
> To do that you need to build syzkaller, and copy ./bin/syz-execprog
> and ./bin/syz-executor into your testing environment, and then do:
>
> ./syz-execprog -sandbox=none -repeat=0 -procs=6 ./repro.prog
>
Thanks for the tips on your environment.
thanks,
-- Shuah
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