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

[Shuah Khan]

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@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?
>
> 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