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Wed, 12 Aug 2026 17:58:06 +0000 (GMT) Received: from [9.61.74.89] (unknown [9.61.74.89]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Aug 2026 17:58:06 +0000 (GMT) Message-ID: Date: Wed, 12 Aug 2026 13:58:06 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 8/9] s390/vfio-ap: Fix NULL deref in status_show() during queue probe To: Anthony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: jjherne@linux.ibm.com, borntraeger@de.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, kwankhede@nvidia.com, fiuczy@linux.ibm.com, pbonzini@redhat.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, agordeev@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, stable@vger.kernel.org References: <20260812170945.738351-1-akrowiak@linux.ibm.com> <20260812170945.738351-9-akrowiak@linux.ibm.com> From: Matthew Rosato Content-Language: en-US In-Reply-To: <20260812170945.738351-9-akrowiak@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=XqfK/1F9 c=1 sm=1 tr=0 ts=6a7cb431 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=bFAEpDOKK8sSTV94CGcA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEyMDE0MiBTYWx0ZWRfX5QMcnOopf4Gb SIpoNzdhEMy0nUdnFXLfjESnoQKThS1VxzyVCyFPXygaVc4GxvPgnLYY9dA5694yUWW2OLYIhzN tNC6wbyibPlAi0uncWdIsihugWVKNb8+YkjEQDCajbs8CXxmUx9pJV2HSKZfbUBo8+Rzf54PLZU qoqKX8ORALF0pERytPZPTUqI/IHxor95D1oOQBGNfSo6lZ30c702SOuiK+qNKYONKpwXVcUaWV/ poZHGWs/IjyNRA6wY0YYtVoLoPEz8mLYEg0eelWUkqL5XQc0SeaVx+J/171IaY9a47T24M4gf5c nu+B2Xw3/R0L7enNhO9ZLntZcRbiK42hxOWzqizea580MTD1IMBAjiF/+g0tD7FgHGV5oJGub7a Dkd7ufT9wsTiViN2Ib6x3sPU6bSJO+v7l/IqwIlYeLJMomIo/urNyiK84UPZk2EmNr0gWy4w7JG 7VVeUHRHEQbrBNEicSw== X-Proofpoint-ORIG-GUID: M-G0qlt-YSFuzhp-Ue06Z62Vg3rVhhhW X-Proofpoint-GUID: M-G0qlt-YSFuzhp-Ue06Z62Vg3rVhhhW X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDE0MiBTYWx0ZWRfX0wSCFs4IVWyN VUNxMk1lz68c3uIiQfEI8nZlBkkVqCphyjt+n3aDKfTnBMWGL9xw9B8yWpmUSps4NwAjTnhXrcI x0BsWbQv4xrPgYLsJEFw3Ic7Xi67H0Q= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-12_05,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 spamscore=0 adultscore=0 malwarescore=0 clxscore=1015 suspectscore=0 priorityscore=1501 impostorscore=0 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120142 On 8/12/26 1:09 PM, Anthony Krowiak wrote: > 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 > --- > drivers/s390/crypto/vfio_ap_ops.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c > index 16779cfc64e8..b0454a296c67 100644 > --- a/drivers/s390/crypto/vfio_ap_ops.c > +++ b/drivers/s390/crypto/vfio_ap_ops.c > @@ -2424,14 +2424,17 @@ 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) { > @@ -2439,11 +2442,10 @@ 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); > @@ -2472,8 +2474,13 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) > return ret; > > err_remove_group: > + release_update_locks_for_mdev(matrix_mdev); I think now you've just shrunk the window instead of totally closed it? Can't sysfs still be accessed between this release and the remove_group? Do you think adding an additional NULL check against dev_get_drvdata() in status_show() and treating the NULL case like the other error conditions would be enough to cover that window?