From dd6f4ef6f8a37412909ad787c837332fb070159c Mon Sep 17 00:00:00 2001 From: Anthony Krowiak Date: Wed, 12 Aug 2026 16:02:39 -0400 Subject: [PATCH] s390/vfio-ap: Fix NULL deref in status_show() during queue probe MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When vfio_ap_mdev_probe_queue() creates the sysfs attribute group, the queue's driver data has not yet been set. A concurrent read of the 'status' attribute can therefore call dev_get_drvdata() and get NULL, which is then passed directly to vfio_ap_mdev_for_queue() where q->apqn is unconditionally dereferenced, causing a NULL pointer dereference. Fix this by acquiring the update locks before calling sysfs_create_group(). The status_show() function acquires guests_lock before reading the driver data, so any concurrent read will block until after dev_set_drvdata() has been called and the update locks are released. As a bonus, the APQN no longer needs to be read from the queue struct after allocation — it can be read directly from apdev before allocation and stored in a local variable, which is then assigned to q->apqn once the allocation succeeds. Fixes: 260f3ea141382 ("s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak Reviewed-by: Matthew Rosato Signed-off-by: Christian Borntraeger --- drivers/s390/crypto/vfio_ap_ops.c | 33 +++++++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 4 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 1546a216295b..940c0ff668be 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -2321,6 +2321,23 @@ static ssize_t status_show(struct device *dev, mutex_lock(&matrix_dev->guests_lock); mutex_lock(&matrix_dev->mdevs_lock); q = dev_get_drvdata(&apdev->device); + + /* + * Make sure the drvdata has been set before proceeding. There is a + * possibility that the drvdata was not set if the vfio_ap_queue object + * could not be allocated when the queue device was probed. In that case, + * the locks used in vfio_ap_mdev_probe_queue() are released prior to + * removing the sysfs status attribute to avoid a lockdep + * splat. That opens a very small window where the status attribute is + * still available without the vfio_ap_queue object having been + * stored in the device drvdata. In that case, indicate the queue is not + * assigned. + */ + if (!q) { + nchars = sysfs_emit(buf, "%s\n", AP_QUEUE_UNASSIGNED); + goto done; + } + matrix_mdev = vfio_ap_mdev_for_queue(q); /* If the queue is assigned to the matrix mediated device, then @@ -2345,6 +2362,7 @@ static ssize_t status_show(struct device *dev, nchars = sysfs_emit(buf, "%s\n", AP_QUEUE_UNASSIGNED); } +done: mutex_unlock(&matrix_dev->mdevs_lock); mutex_unlock(&matrix_dev->guests_lock); @@ -2419,14 +2437,17 @@ void vfio_ap_mdev_unregister(void) int vfio_ap_mdev_probe_queue(struct ap_device *apdev) { - int ret; + int ret, apqn; struct vfio_ap_queue *q; DECLARE_BITMAP(apm_filtered, AP_DEVICES); struct ap_matrix_mdev *matrix_mdev; + apqn = to_ap_queue(&apdev->device)->qid; + matrix_mdev = get_update_locks_by_apqn(apqn); + ret = sysfs_create_group(&apdev->device.kobj, &vfio_queue_attr_group); if (ret) - return ret; + goto err_release_locks; q = kzalloc_obj(*q); if (!q) { @@ -2434,11 +2455,10 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) goto err_remove_group; } - q->apqn = to_ap_queue(&apdev->device)->qid; + q->apqn = apqn; q->saved_isc = VFIO_AP_ISC_INVALID; memset(&q->reset_status, 0, sizeof(q->reset_status)); INIT_WORK(&q->reset_work, apq_reset_check); - matrix_mdev = get_update_locks_by_apqn(q->apqn); if (matrix_mdev) { vfio_ap_mdev_link_queue(matrix_mdev, q); @@ -2467,8 +2487,13 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) return ret; err_remove_group: + release_update_locks_for_mdev(matrix_mdev); sysfs_remove_group(&apdev->device.kobj, &vfio_queue_attr_group); return ret; + +err_release_locks: + release_update_locks_for_mdev(matrix_mdev); + return ret; } void vfio_ap_mdev_remove_queue(struct ap_device *apdev)