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Date: Wed, 7 Oct 2020 07:56:54 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Andrey Konovalov <andreyknvl@...gle.com>,
Shuah Khan <shuah@...nel.org>,
Valentina Manea <valentina.manea.m@...il.com>
Cc: 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 10/5/20 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
I do see the messages during shutdown - stop threads etc.
What am I missing?
thanks,
-- Shuah
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