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

[Shuah Khan]

On 10/7/20 4:30 AM, Hillf Danton wrote:
> Mon, 05 Oct 2020 06:59:19
> > 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..
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> >
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> > syzbot can test patches for this issue, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
>
> Add a state for vhci device to avoid stop more than once.

It is better for it be called more than once and protect the
paths.

I am working on a fix for this.

thanks,
-- Shuah