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    Subject[PATCH 4.14 044/126] HID: hiddev: Fix race in in hiddev_disconnect()
    Date
    From: dan.carpenter@oracle.com <dan.carpenter@oracle.com>

    commit 5c02c447eaeda29d3da121a2e17b97ccaf579b51 upstream.

    Syzbot reports that "hiddev" is used after it's free in hiddev_disconnect().
    The hiddev_disconnect() function sets "hiddev->exist = 0;" so
    hiddev_release() can free it as soon as we drop the "existancelock"
    lock. This patch moves the mutex_unlock(&hiddev->existancelock) until
    after we have finished using it.

    Reported-by: syzbot+784ccb935f9900cc7c9e@syzkaller.appspotmail.com
    Fixes: 7f77897ef2b6 ("HID: hiddev: fix potential use-after-free")
    Suggested-by: Alan Stern <stern@rowland.harvard.edu>
    Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.cz>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/hid/usbhid/hiddev.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/hid/usbhid/hiddev.c
    +++ b/drivers/hid/usbhid/hiddev.c
    @@ -954,9 +954,9 @@ void hiddev_disconnect(struct hid_device
    hiddev->exist = 0;

    if (hiddev->open) {
    - mutex_unlock(&hiddev->existancelock);
    hid_hw_close(hiddev->hid);
    wake_up_interruptible(&hiddev->wait);
    + mutex_unlock(&hiddev->existancelock);
    } else {
    mutex_unlock(&hiddev->existancelock);
    kfree(hiddev);

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