[PATCH 2/3] s390/dasd: Fix potential NULL pointer dereference

[Stefan Haberland <sth@linux.ibm.com>]

From: Jan Höppner <hoeppner@linux.ibm.com>

dasd_release_space() checks the implementation of the is_ese()
discipline function before calling it to determine if a given device is
an ESE DASD.

The current usage of the logical AND operator will lead to a NULL
pointer dereference as the function is called even if the function
pointer is NULL.

Fix this by using the logical OR operator.

Fixes: 91dc4a197569 ("s390/dasd: Add new ioctl to release space")
Cc: stable@vger.kernel.org # v5.3+
Reported-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Eduard Shishkin <edward6@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
---
 drivers/s390/block/dasd_ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/block/dasd_ioctl.c b/drivers/s390/block/dasd_ioctl.c
index c85ee42732a3..e5b8b413f5ab 100644
--- a/drivers/s390/block/dasd_ioctl.c
+++ b/drivers/s390/block/dasd_ioctl.c
@@ -324,7 +324,7 @@ static int dasd_ioctl_check_format(struct block_device *bdev, void __user *argp)
 static int dasd_release_space(struct dasd_device *device,
 			      struct format_data_t *rdata)
 {
-	if (!device->discipline->is_ese && !device->discipline->is_ese(device))
+	if (!device->discipline->is_ese || !device->discipline->is_ese(device))
 		return -ENOTSUPP;
 	if (!device->discipline->release_space)
 		return -ENOTSUPP;
-- 
2.53.0