[PATCH v4 4/9] s390/vfio-ap: Fix required lock not held during update of ap_matrix_mdev object

[Anthony Krowiak <akrowiak@linux.ibm.com>]

In the vfio_ap_mdev_cfg_add function, the apm_add, aqm_add and adm_add
fields of an ap_matrix_mdev object fields are modified while not holding
the matrix_dev->mdevs_lock. This lock must be held while making these
to guard against a race condition with another caller that may be
concurrently modifying these fields or any of the fields in the
matrix_mdev->matrix.

Fixes: eeb386aeb5b7c ("s390/vfio-ap: handle config changed and scan complete notification")
Cc: stable@vger.kernel.org
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index f2d662e388bd..21c502598f8c 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -2777,12 +2777,20 @@ static void vfio_ap_mdev_cfg_add(unsigned long *apm_add, unsigned long *aqm_add,
 	 * called.
 	 */
 	list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) {
+		/*
+		 * The mdevs_lock must be held in order to access fields
+		 * within matrix_mdev
+		 */
+		mutex_lock(&matrix_dev->mdevs_lock);
+
 		bitmap_and(matrix_mdev->apm_add,
 			   matrix_mdev->matrix.apm, apm_add, AP_DEVICES);
 		bitmap_and(matrix_mdev->aqm_add,
 			   matrix_mdev->matrix.aqm, aqm_add, AP_DOMAINS);
 		bitmap_and(matrix_mdev->adm_add,
 			   matrix_mdev->matrix.adm, adm_add, AP_DEVICES);
+
+		mutex_unlock(&matrix_dev->mdevs_lock);
 	}
 }
 
-- 
2.53.0