linux-kernel - [PATCH] s390: cio: fix use-after-free in ccw_device_destroy

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Date:   Tue, 1 Dec 2020 14:31:50 +0800
From:   Qinglang Miao <miaoqinglang@...wei.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        "Heiko Carstens" <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        "Christian Borntraeger" <borntraeger@...ibm.com>
CC:     <linux-s390@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Qinglang Miao" <miaoqinglang@...wei.com>
Subject: [PATCH] s390: cio: fix use-after-free in ccw_device_destroy_console

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")
Reported-by: Hulk Robot <hulkci@...wei.com>
Suggested-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Qinglang Miao <miaoqinglang@...wei.com>
---
 This patch is indeed a v2 of older one. Considering that the
 patch's name has changed, I think a normal prefix 'PATCH' is
 better.

 drivers/s390/cio/device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index b29fe8d50..33280ca18 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);
 	kfree(io_priv);
 }
 
-- 
2.23.0