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

[Ben Hutchings]

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

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

From: Halil Pasic <pa...@linux.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 <pa...@linux.ibm.com>
Message-Id: <20180925121309.58524-2-pa...@linux.ibm.com>
Signed-off-by: Cornelia Huck <coh...@redhat.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <b...@decadent.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;