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    Subject[PATCH 4.14 17/65] USB: iowarrior: fix use-after-free on disconnect
    Date
    From: Johan Hovold <johan@kernel.org>

    commit edc4746f253d907d048de680a621e121517f484b upstream.

    A recent fix addressing a deadlock on disconnect introduced a new bug
    by moving the present flag out of the critical section protected by the
    driver-data mutex. This could lead to a racing release() freeing the
    driver data before disconnect() is done with it.

    Due to insufficient locking a related use-after-free could be triggered
    also before the above mentioned commit. Specifically, the driver needs
    to hold the driver-data mutex also while checking the opened flag at
    disconnect().

    Fixes: c468a8aa790e ("usb: iowarrior: fix deadlock on disconnect")
    Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
    Cc: stable <stable@vger.kernel.org> # 2.6.21
    Reported-by: syzbot+0761012cebf7bdb38137@syzkaller.appspotmail.com
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Link: https://lore.kernel.org/r/20191009104846.5925-2-johan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/misc/iowarrior.c | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    --- a/drivers/usb/misc/iowarrior.c
    +++ b/drivers/usb/misc/iowarrior.c
    @@ -870,8 +870,6 @@ static void iowarrior_disconnect(struct
    dev = usb_get_intfdata(interface);
    mutex_lock(&iowarrior_open_disc_lock);
    usb_set_intfdata(interface, NULL);
    - /* prevent device read, write and ioctl */
    - dev->present = 0;

    minor = dev->minor;
    mutex_unlock(&iowarrior_open_disc_lock);
    @@ -882,8 +880,7 @@ static void iowarrior_disconnect(struct
    mutex_lock(&dev->mutex);

    /* prevent device read, write and ioctl */
    -
    - mutex_unlock(&dev->mutex);
    + dev->present = 0;

    if (dev->opened) {
    /* There is a process that holds a filedescriptor to the device ,
    @@ -893,8 +890,10 @@ static void iowarrior_disconnect(struct
    usb_kill_urb(dev->int_in_urb);
    wake_up_interruptible(&dev->read_wait);
    wake_up_interruptible(&dev->write_wait);
    + mutex_unlock(&dev->mutex);
    } else {
    /* no process is using the device, cleanup now */
    + mutex_unlock(&dev->mutex);
    iowarrior_delete(dev);
    }


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