Re: KASAN: null-ptr-deref Write in event_handler

From: Shuah Khan <skhan@linuxfoundation.org>
To: Andrey Konovalov <andreyknvl@google.com>,
	Shuah Khan <shuah@kernel.org>,
	Valentina Manea <valentina.manea.m@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	USB list <linux-usb@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	syzbot <syzbot+bf1a360e305ee719e364@syzkaller.appspotmail.com>,
	Nazime Hande Harputluoglu <handeharputlu@google.com>,
	Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: KASAN: null-ptr-deref Write in event_handler
Date: Mon, 5 Oct 2020 14:44:20 -0600	[thread overview]
Message-ID: <2947473d-76cd-a663-049a-4d51a97e2a3e@linuxfoundation.org> (raw)
In-Reply-To: <CAAeHK+xWQp87S=bF2RfUjcudGaLVjk3yKLL-bxRzVM=YNRtzRA@mail.gmail.com>

On 10/5/20 8:04 AM, Andrey Konovalov wrote:
> On Mon, Oct 5, 2020 at 3:59 PM syzbot
> <syzbot+bf1a360e305ee719e364@syzkaller.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@syzkaller.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.

thanks,
-- Shuah