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Date:   Fri, 20 Nov 2020 15:48:50 +0800
From:   Qinglang Miao <miaoqinglang@...wei.com>
To:     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: cmf: fix use-after-free in enable_cmf

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@...wei.com>
Signed-off-by: Qinglang Miao <miaoqinglang@...wei.com>
---
 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);
+		return ret;
+	}
 out_unlock:
 	device_unlock(&cdev->dev);
 	return ret;
-- 
2.23.0

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