linux-kernel - Re: KASAN: null-ptr-deref Write in event

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Message-ID: <CAAeHK+wZGwovnT969F-aq+EzH8-K21GxJ7YJ0S0Ynd4GM_B4kA@mail.gmail.com>
Date:   Wed, 7 Oct 2020 16:28:58 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
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>
Subject: Re: KASAN: null-ptr-deref Write in event_handler

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?

>
> 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!