From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40622 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729165AbeIYSUz (ORCPT ); Tue, 25 Sep 2018 14:20:55 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w8PC413u059601 for ; Tue, 25 Sep 2018 08:13:38 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2mqjxrw7nf-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 25 Sep 2018 08:13:37 -0400 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 25 Sep 2018 13:13:35 +0100 From: Halil Pasic To: Cornelia Huck , Halil Pasic , linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Cc: stable@vger.kernel.org, Colin Ian King , Christian Borntraeger Subject: [PATCH v2 2/2] virtio/s390: fix race in ccw_io_helper() Date: Tue, 25 Sep 2018 14:13:09 +0200 In-Reply-To: <20180925121309.58524-1-pasic@linux.ibm.com> References: <20180925121309.58524-1-pasic@linux.ibm.com> Message-Id: <20180925121309.58524-3-pasic@linux.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: While ccw_io_helper() seems like intended to be exclusive in a sense that it is supposed to facilitate I/O for at most one thread at any given time, there is actually nothing ensuring that threads won't pile up at vcdev->wait_q. If they do, all threads get woken up and see the status that belongs to some other request than their own. This can lead to bugs. For an example see: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1788432 This race normally does not cause any problems. The operations provided by struct virtio_config_ops are usually invoked in a well defined sequence, normally don't fail, and are normally used quite infrequent too. Yet, if some of the these operations are directly triggered via sysfs attributes, like in the case described by the referenced bug, userspace is given an opportunity to force races by increasing the frequency of the given operations. Let us fix the problem by ensuring, that for each device, we finish processing the previous request before starting with a new one. Signed-off-by: Halil Pasic Reported-by: Colin Ian King Cc: stable@vger.kernel.org --- drivers/s390/virtio/virtio_ccw.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c index a5e8530a3391..b67dc4974f23 100644 --- a/drivers/s390/virtio/virtio_ccw.c +++ b/drivers/s390/virtio/virtio_ccw.c @@ -56,6 +56,7 @@ struct virtio_ccw_device { unsigned int revision; /* Transport revision */ wait_queue_head_t wait_q; spinlock_t lock; + struct mutex io_lock; /* Serializes I/O requests */ struct list_head virtqueues; unsigned long indicators; unsigned long indicators2; @@ -296,6 +297,7 @@ static int ccw_io_helper(struct virtio_ccw_device *vcdev, unsigned long flags; int flag = intparm & VIRTIO_CCW_INTPARM_MASK; + mutex_lock(&vcdev->io_lock); do { spin_lock_irqsave(get_ccwdev_lock(vcdev->cdev), flags); ret = ccw_device_start(vcdev->cdev, ccw, intparm, 0, 0); @@ -308,7 +310,9 @@ static int ccw_io_helper(struct virtio_ccw_device *vcdev, cpu_relax(); } while (ret == -EBUSY); wait_event(vcdev->wait_q, doing_io(vcdev, flag) == 0); - return ret ? ret : vcdev->err; + ret = ret ? ret : vcdev->err; + mutex_unlock(&vcdev->io_lock); + return ret; } static void virtio_ccw_drop_indicator(struct virtio_ccw_device *vcdev, @@ -1253,6 +1257,7 @@ static int virtio_ccw_online(struct ccw_device *cdev) init_waitqueue_head(&vcdev->wait_q); INIT_LIST_HEAD(&vcdev->virtqueues); spin_lock_init(&vcdev->lock); + mutex_init(&vcdev->io_lock); spin_lock_irqsave(get_ccwdev_lock(cdev), flags); dev_set_drvdata(&cdev->dev, vcdev); -- 2.16.4