From patchwork Tue Mar 19 16:15:01 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Bader X-Patchwork-Id: 1058533 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=lists.ubuntu.com (client-ip=91.189.94.19; helo=huckleberry.canonical.com; envelope-from=kernel-team-bounces@lists.ubuntu.com; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=canonical.com Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 44Nynh3BqVz9s9T; Wed, 20 Mar 2019 03:15:20 +1100 (AEDT) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.86_2) (envelope-from ) id 1h6HOM-0002s0-2W; Tue, 19 Mar 2019 16:15:06 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtps (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.86_2) (envelope-from ) id 1h6HOI-0002rE-Bb for kernel-team@lists.ubuntu.com; Tue, 19 Mar 2019 16:15:02 +0000 Received: from 2.general.smb.uk.vpn ([10.172.193.29] helo=canonical.com) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.76) (envelope-from ) id 1h6HOH-0006l5-Up for kernel-team@lists.ubuntu.com; Tue, 19 Mar 2019 16:15:01 +0000 From: Stefan Bader To: kernel-team@lists.ubuntu.com Subject: [SRU B/C: 2/2] virtio/s390: fix race in ccw_io_helper() Date: Tue, 19 Mar 2019 16:15:01 +0000 Message-Id: <20190319161501.29267-3-stefan.bader@canonical.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190319161501.29267-1-stefan.bader@canonical.com> References: <20190319161501.29267-1-stefan.bader@canonical.com> X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.20 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: "kernel-team" From: Halil Pasic BugLink: https://bugs.launchpad.net/bugs/1788432 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 Message-Id: <20180925121309.58524-3-pasic@linux.ibm.com> Signed-off-by: Cornelia Huck Signed-off-by: Michael S. Tsirkin (cherry picked from commit 78b1a52e05c9db11d293342e8d6d8a230a04b4e7) Signed-off-by: Stefan Bader --- 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 c94f38ef9a94..c9c57b4a0b71 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);