[PATCH] s390/cio: Fix NULL dereference in ccw_device_get_util_str()

[Vineeth Vijayan <vneethv@linux.ibm.com>]

The channel path registry entry associated with a CHPID may be removed
while the subchannel's PMCW still references that CHPID. In this case,
chpid_to_chp() can return NULL, leading to a NULL pointer dereference.
 
Add the missing NULL check before dereferencing the returned pointer.

Fixes: 199652309a4d ("s390/cio: add helper to query utility strings per given ccw device")
Cc: stable@vger.kernel.org
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
---
 drivers/s390/cio/device_ops.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/s390/cio/device_ops.c b/drivers/s390/cio/device_ops.c
index f2f7f8cba410..1f7e83fd5087 100644
--- a/drivers/s390/cio/device_ops.c
+++ b/drivers/s390/cio/device_ops.c
@@ -517,6 +517,8 @@ u8 *ccw_device_get_util_str(struct ccw_device *cdev, int chp_idx)
 	chp_id_init(&chpid);
 	chpid.id = sch->schib.pmcw.chpid[chp_idx];
 	chp = chpid_to_chp(chpid);
+	if (!chp)
+		return NULL;
 
 	util_str = kmalloc(sizeof(chp->desc_fmt3.util_str), GFP_KERNEL);
 	if (!util_str)
-- 
2.53.0