linux-kernel - [PATCH 3.16 271/305] virtio/s390: avoid race on vcdev->config

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Message-ID: <lsq.1549201508.887204213@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Halil Pasic" <pasic@...ux.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Cornelia Huck" <cohuck@...hat.com>
Subject: [PATCH 3.16 271/305] virtio/s390: avoid race on vcdev->config

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Halil Pasic <pasic@...ux.ibm.com>

commit 2448a299ec416a80f699940a86f4a6d9a4f643b1 upstream.

Currently we have a race on vcdev->config in virtio_ccw_get_config() and
in virtio_ccw_set_config().

This normally does not cause problems, as these are usually infrequent
operations. However, for some devices writing to/reading from the config
space can be triggered through sysfs attributes. For these, userspace can
force the race by increasing the frequency.

Signed-off-by: Halil Pasic <pasic@...ux.ibm.com>
Message-Id: <20180925121309.58524-2-pasic@...ux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/s390/kvm/virtio_ccw.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -741,6 +741,7 @@ static void virtio_ccw_get_config(struct
 	int ret;
 	struct ccw1 *ccw;
 	void *config_area;
+	unsigned long flags;
 
 	ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
 	if (!ccw)
@@ -759,11 +760,13 @@ static void virtio_ccw_get_config(struct
 	if (ret)
 		goto out_free;
 
+	spin_lock_irqsave(&vcdev->lock, flags);
 	memcpy(vcdev->config, config_area, offset + len);
-	if (buf)
-		memcpy(buf, &vcdev->config[offset], len);
 	if (vcdev->config_ready < offset + len)
 		vcdev->config_ready = offset + len;
+	spin_unlock_irqrestore(&vcdev->lock, flags);
+	if (buf)
+		memcpy(buf, config_area + offset, len);
 
 out_free:
 	kfree(config_area);
@@ -777,6 +780,7 @@ static void virtio_ccw_set_config(struct
 	struct virtio_ccw_device *vcdev = to_vc_device(vdev);
 	struct ccw1 *ccw;
 	void *config_area;
+	unsigned long flags;
 
 	ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);
 	if (!ccw)
@@ -789,9 +793,11 @@ static void virtio_ccw_set_config(struct
 	/* Make sure we don't overwrite fields. */
 	if (vcdev->config_ready < offset)
 		virtio_ccw_get_config(vdev, 0, NULL, offset);
+	spin_lock_irqsave(&vcdev->lock, flags);
 	memcpy(&vcdev->config[offset], buf, len);
 	/* Write the config area to the host. */
 	memcpy(config_area, vcdev->config, sizeof(vcdev->config));
+	spin_unlock_irqrestore(&vcdev->lock, flags);
 	ccw->cmd_code = CCW_CMD_WRITE_CONF;
 	ccw->flags = 0;
 	ccw->count = offset + len;