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    Subject[PATCH 5.3 040/112] USB: legousbtower: fix deadlock on disconnect
    Date
    From: Johan Hovold <johan@kernel.org>

    commit 33a7813219f208f4952ece60ee255fd983272dec upstream.

    Fix a potential deadlock if disconnect races with open.

    Since commit d4ead16f50f9 ("USB: prevent char device open/deregister
    race") core holds an rw-semaphore while open is called and when
    releasing the minor number during deregistration. This can lead to an
    ABBA deadlock if a driver takes a lock in open which it also holds
    during deregistration.

    This effectively reverts commit 78663ecc344b ("USB: disconnect open race
    in legousbtower") which needlessly introduced this issue after a generic
    fix for this race had been added to core by commit d4ead16f50f9 ("USB:
    prevent char device open/deregister race").

    Fixes: 78663ecc344b ("USB: disconnect open race in legousbtower")
    Cc: stable <stable@vger.kernel.org> # 2.6.24
    Reported-by: syzbot+f9549f5ee8a5416f0b95@syzkaller.appspotmail.com
    Tested-by: syzbot+f9549f5ee8a5416f0b95@syzkaller.appspotmail.com
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Link: https://lore.kernel.org/r/20190919083039.30898-3-johan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/misc/legousbtower.c | 19 ++-----------------
    1 file changed, 2 insertions(+), 17 deletions(-)

    --- a/drivers/usb/misc/legousbtower.c
    +++ b/drivers/usb/misc/legousbtower.c
    @@ -179,7 +179,6 @@ static const struct usb_device_id tower_
    };

    MODULE_DEVICE_TABLE (usb, tower_table);
    -static DEFINE_MUTEX(open_disc_mutex);

    #define LEGO_USB_TOWER_MINOR_BASE 160

    @@ -332,18 +331,14 @@ static int tower_open (struct inode *ino
    goto exit;
    }

    - mutex_lock(&open_disc_mutex);
    dev = usb_get_intfdata(interface);
    -
    if (!dev) {
    - mutex_unlock(&open_disc_mutex);
    retval = -ENODEV;
    goto exit;
    }

    /* lock this device */
    if (mutex_lock_interruptible(&dev->lock)) {
    - mutex_unlock(&open_disc_mutex);
    retval = -ERESTARTSYS;
    goto exit;
    }
    @@ -351,12 +346,10 @@ static int tower_open (struct inode *ino

    /* allow opening only once */
    if (dev->open_count) {
    - mutex_unlock(&open_disc_mutex);
    retval = -EBUSY;
    goto unlock_exit;
    }
    dev->open_count = 1;
    - mutex_unlock(&open_disc_mutex);

    /* reset the tower */
    result = usb_control_msg (dev->udev,
    @@ -423,10 +416,9 @@ static int tower_release (struct inode *

    if (dev == NULL) {
    retval = -ENODEV;
    - goto exit_nolock;
    + goto exit;
    }

    - mutex_lock(&open_disc_mutex);
    if (mutex_lock_interruptible(&dev->lock)) {
    retval = -ERESTARTSYS;
    goto exit;
    @@ -456,10 +448,7 @@ static int tower_release (struct inode *

    unlock_exit:
    mutex_unlock(&dev->lock);
    -
    exit:
    - mutex_unlock(&open_disc_mutex);
    -exit_nolock:
    return retval;
    }

    @@ -912,7 +901,6 @@ static int tower_probe (struct usb_inter
    if (retval) {
    /* something prevented us from registering this driver */
    dev_err(idev, "Not able to get a minor for this device.\n");
    - usb_set_intfdata (interface, NULL);
    goto error;
    }
    dev->minor = interface->minor;
    @@ -944,16 +932,13 @@ static void tower_disconnect (struct usb
    int minor;

    dev = usb_get_intfdata (interface);
    - mutex_lock(&open_disc_mutex);
    - usb_set_intfdata (interface, NULL);

    minor = dev->minor;

    - /* give back our minor */
    + /* give back our minor and prevent further open() */
    usb_deregister_dev (interface, &tower_class);

    mutex_lock(&dev->lock);
    - mutex_unlock(&open_disc_mutex);

    /* if the device is not opened, then we clean up right now */
    if (!dev->open_count) {

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