Re: possible deadlock in usb_deregister_dev (2)

[Andrey Konovalov]

On Tue, Sep 17, 2019 at 10:01 AM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
>
> On Mon, 16 Sep 2019 14:42:06 -0700
> >
> > syzbot has found a reproducer for the following crash on:
> >
> > HEAD commit:    f0df5c1b usb-fuzzer: main usb gadget fuzzer driver
> > git tree:       https://github.com/google/kasan.git usb-fuzzer
> > console output: https://syzkaller.appspot.com/x/log.txt?x=175cdb95600000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
> > dashboard link: https://syzkaller.appspot.com/bug?extid=f9549f5ee8a5416f0b95
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13961369600000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139c811d600000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+f9549f5ee8a5416f0b95@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 5.3.0-rc7+ #0 Not tainted
> > ------------------------------------------------------
> > kworker/0:1/12 is trying to acquire lock:
> > 0000000098630ee4 (minor_rwsem){++++}, at: usb_deregister_dev+0x95/0x230
> > drivers/usb/core/file.c:239
> >
> > but task is already holding lock:
> > 00000000d9ad5b6f (open_disc_mutex){+.+.}, at: tower_disconnect+0x45/0x300
> > drivers/usb/misc/legousbtower.c:945
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #1 (open_disc_mutex){+.+.}:
> >         __mutex_lock_common kernel/locking/mutex.c:930 [inline]
> >         __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1077
> >         tower_open+0xce/0x9b0 drivers/usb/misc/legousbtower.c:335
> >         usb_open+0x1df/0x270 drivers/usb/core/file.c:48
> >         chrdev_open+0x219/0x5c0 fs/char_dev.c:414
> >         do_dentry_open+0x494/0x1120 fs/open.c:797
> >         do_last fs/namei.c:3416 [inline]
> >         path_openat+0x1430/0x3f50 fs/namei.c:3533
> >         do_filp_open+0x1a1/0x280 fs/namei.c:3563
> >         do_sys_open+0x3c0/0x580 fs/open.c:1089
> >         do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
> >         entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > -> #0 (minor_rwsem){++++}:
> >         check_prev_add kernel/locking/lockdep.c:2405 [inline]
> >         check_prevs_add kernel/locking/lockdep.c:2507 [inline]
> >         validate_chain kernel/locking/lockdep.c:2897 [inline]
> >         __lock_acquire+0x1f7c/0x3b50 kernel/locking/lockdep.c:3880
> >         lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4412
> >         down_write+0x92/0x150 kernel/locking/rwsem.c:1500
> >         usb_deregister_dev+0x95/0x230 drivers/usb/core/file.c:239
> >         tower_disconnect+0xa8/0x300 drivers/usb/misc/legousbtower.c:951
> >         usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
> >         __device_release_driver drivers/base/dd.c:1134 [inline]
> >         device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165
> >         bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:556
> >         device_del+0x420/0xb10 drivers/base/core.c:2339
> >         usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
> >         usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
> >         hub_port_connect drivers/usb/core/hub.c:4949 [inline]
> >         hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
> >         port_event drivers/usb/core/hub.c:5359 [inline]
> >         hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
> >         process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
> >         worker_thread+0x96/0xe20 kernel/workqueue.c:2415
> >         kthread+0x318/0x420 kernel/kthread.c:255
> >         ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> >
> > other info that might help us debug this:
> >
> >   Possible unsafe locking scenario:
> >
> >         CPU0                    CPU1
> >         ----                    ----
> >    lock(open_disc_mutex);
> >                                 lock(minor_rwsem);
> >                                 lock(open_disc_mutex);
> >    lock(minor_rwsem);
> >
> >   *** DEADLOCK ***
>
> Fix 78663ecc344b

Hi Hillf,

Thanks for looking at these bugs. This bug has a reproducer, so you
can ask syzbot to test the fix by issuing a syz test command as
described here:

https://github.com/google/syzkaller/blob/master/docs/syzbot.md#usb-bugs

Thanks!

>
> --- a/drivers/usb/misc/legousbtower.c
> +++ b/drivers/usb/misc/legousbtower.c
> @@ -941,17 +941,31 @@ static void tower_disconnect (struct usb
>         struct lego_usb_tower *dev;
>         int minor;
>
> -       dev = usb_get_intfdata (interface);
>         mutex_lock(&open_disc_mutex);
> +       dev = usb_get_intfdata (interface);
>         usb_set_intfdata (interface, NULL);
>
>         minor = dev->minor;
>
> -       /* give back our minor */
> -       usb_deregister_dev (interface, &tower_class);
> -
>         mutex_lock(&dev->lock);
>         mutex_unlock(&open_disc_mutex);
> +       /*
> +        * give back our minor out of open_disc_mutex to shun deadlock like
> +
> +               Possible unsafe locking scenario:
> +
> +               CPU0                    CPU1
> +               ----                    ----
> +               disconnect path         open path
> +
> +               lock(open_disc_mutex);
> +                                       lock(minor_rwsem);
> +                                       lock(open_disc_mutex);
> +               lock(minor_rwsem);
> +
> +        * and we can do this since intfdata is reset with lock held.
> +        */
> +       usb_deregister_dev (interface, &tower_class);
>
>         /* if the device is not opened, then we clean up right now */
>         if (!dev->open_count) {
>