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

[Andrey Konovalov]

On Mon, Oct 5, 2020 at 3:59 PM syzbot
<syzbot+bf1a360e305ee719e364@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> 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?

Thanks in advance!