Re: possible deadlock in usb_deregister_dev (2)

[Johan Hovold]

On Mon, Sep 16, 2019 at 02:42:06PM -0700, syzbot wrote:
> 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
> 
> usb 1-1: config 0 descriptor??
> legousbtower 1-1:0.219: LEGO USB Tower firmware version is 129.136 build  
> 65535
> legousbtower 1-1:0.219: LEGO USB Tower #-160 now attached to major 180  
> minor 0
> usb 1-1: USB disconnect, device number 2
> ======================================================
> 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 ***

This should be fixed by the below patch. Looks like we may have a
similar issue in a few more drivers. Fixing them up next.

Johan

#syz test: https://github.com/google/kasan.git f0df5c1b