在 2020/11/20 15:55, Cornelia Huck 写道:
On Fri, 20 Nov 2020 15:48:49 +0800
Qinglang Miao <miaoqingl...@huawei.com> wrote:

put_device calls release function which do kfree() inside.
So following use of sch&cdev would cause use-after-free bugs.

Fix these by simply adjusting the position of put_device.

Fixes: 37db8985b211 ("s390/cio: add basic protected virtualization support")
Fixes: 74bd0d859dc3 ("s390/cio: fix unlocked access of online member")
Reported-by: Hulk Robot <hul...@huawei.com>
Signed-off-by: Qinglang Miao <miaoqingl...@huawei.com>
---
  drivers/s390/cio/device.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index b29fe8d50..69492417b 100644
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -1664,10 +1664,10 @@ void __init ccw_device_destroy_console(struct 
ccw_device *cdev)
        struct io_subchannel_private *io_priv = to_io_private(sch);
set_io_private(sch, NULL);
-       put_device(&sch->dev);
-       put_device(&cdev->dev);
        dma_free_coherent(&sch->dev, sizeof(*io_priv->dma_area),
                          io_priv->dma_area, io_priv->dma_area_dma);
+       put_device(&sch->dev);
+       put_device(&cdev->dev);

That change looks reasonable.

        kfree(io_priv);
  }
@@ -1774,8 +1774,8 @@ static int ccw_device_remove(struct device *dev)
                                      ret, cdev->private->dev_id.ssid,
                                      cdev->private->dev_id.devno);
                /* Give up reference obtained in ccw_device_set_online(). */
-               put_device(&cdev->dev);
                spin_lock_irq(cdev->ccwlock);
+               put_device(&cdev->dev);

As the comment above states, the put_device() gives up the reference
obtained in ccw_device_set_online(). There's at least one more
reference remaining (held by the caller of the remove function). Moving
the put_device() does not fix anything here.
Hi, Cornelia

Sorry for the delayed reply.

Your suggestion is reasonable, there is a mistake in this patch for I didn't notice that there would be at least one more reference remaining.

So I sent a new patch only to move put_device after dma_free_coherent. I put the link as below:
https://lore.kernel.org/lkml/20201201063150.82128-1-miaoqingl...@huawei.com/

Thanks!

        }
        ccw_device_set_timeout(cdev, 0);
        cdev->drv = NULL;

.

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