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Message-ID: <CAAeHK+xgZ0=Y32NAjGfGnXpZh=832opkRnmiq2_nZO5dgMNLSw@mail.gmail.com>
Date: Tue, 17 Sep 2019 13:58:40 +0200
From: Andrey Konovalov <andreyknvl@...gle.com>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+f9549f5ee8a5416f0b95@...kaller.appspotmail.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
LKML <linux-kernel@...r.kernel.org>,
USB list <linux-usb@...r.kernel.org>,
Alan Stern <stern@...land.harvard.edu>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: possible deadlock in usb_deregister_dev (2)
On Tue, Sep 17, 2019 at 10:01 AM Hillf Danton <hdanton@...a.com> 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@...kaller.appspotmail.com
> >
> > ======================================================
> > 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) {
>
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