On Fri, 20 Nov 2020 15:48:50 +0800
Qinglang Miao <miaoqinglang@xxxxxxxxxx> wrote:
> kfree(cdev) is called in put_device in the error branch. So that
> device_unlock(&cdev->dev) would raise a use-after-free bug. In fact,
> there's no need to call device_unlock after put_device.
>
> Fix it by adding simply return after put_device.
>
> Fixes: a6ef15652d26 ("s390/cio: fix use after free in cmb processing")
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Signed-off-by: Qinglang Miao <miaoqinglang@xxxxxxxxxx>
> ---
> drivers/s390/cio/cmf.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/cio/cmf.c b/drivers/s390/cio/cmf.c
> index 72dd2471e..e95ca476f 100644
> --- a/drivers/s390/cio/cmf.c
> +++ b/drivers/s390/cio/cmf.c
> @@ -1149,9 +1149,12 @@ int enable_cmf(struct ccw_device *cdev)
> sysfs_remove_group(&cdev->dev.kobj, cmbops->attr_group);
> cmbops->free(cdev);
> }
> +
> out:
> - if (ret)
> + if (ret) {
> put_device(&cdev->dev);
The put_device() here undoes a get_device() further up in the function.
There is at least one more reference remaining, held by the caller of
enable_cmf(). Returning here would actually introduce a bug (missing
unlock).
> + return ret;
> + }
> out_unlock:
> device_unlock(&cdev->dev);
> return ret;
