virtio_net: clear MTU when out of range

virtio attempts to clear the MTU feature bit if the value is out of the
supported range, but this has no real effect since FEATURES_OK has
already been set.

Fix this up by checking the MTU in the new validate callback.

Fixes: 14de9d114a82 ("virtio-net: Add initial MTU advice feature")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit fe36cbe0671e868cbd2f534a50ac60273fa5acf2)

Orabug: 26584452

Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Conflicts:
	drivers/net/virtio_net.c
Due to the lack of commit d0c2c9973ecd ("net: use core MTU range
checking in virt drivers") the MTU size check is still done in the
virtio_net.

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4f0b08363073d8990f2d4e4db62e9919408482c2..84da82b8555e09e3f20b16bebae7ae00ceae7b36 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1713,14 +1713,8 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
        return true;
 }
 
-static int virtnet_probe(struct virtio_device *vdev)
+static int virtnet_validate(struct virtio_device *vdev)
 {
-       int i, err;
-       struct net_device *dev;
-       struct virtnet_info *vi;
-       u16 max_queue_pairs;
-       int mtu;
-
        if (!vdev->config->get) {
                dev_err(&vdev->dev, "%s failure: config access disabled\n",
                        __func__);
@@ -1730,6 +1724,25 @@ static int virtnet_probe(struct virtio_device *vdev)
        if (!virtnet_validate_features(vdev))
                return -EINVAL;
 
+       if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
+               int mtu = virtio_cread16(vdev,
+                                        offsetof(struct virtio_net_config,
+                                                 mtu));
+               if (mtu < MIN_MTU || mtu > MAX_MTU)
+                       __virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
+       }
+
+       return 0;
+}
+
+static int virtnet_probe(struct virtio_device *vdev)
+{
+       int i, err;
+       struct net_device *dev;
+       struct virtnet_info *vi;
+       u16 max_queue_pairs;
+       int mtu;
+
        /* Find if host supports multiqueue virtio_net device */
        err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
                                   struct virtio_net_config,
@@ -1840,8 +1853,15 @@ static int virtnet_probe(struct virtio_device *vdev)
                mtu = virtio_cread16(vdev,
                                     offsetof(struct virtio_net_config,
                                              mtu));
-               if (virtnet_change_mtu(dev, mtu))
-                       __virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
+               if (virtnet_change_mtu(dev, mtu)) {
+                       /* Should never trigger: MTU was previously validated
+                        * in virtnet_validate.
+                        */
+                       dev_err(&vdev->dev, "device MTU appears to have changed "
+                               "it is now %d out of range [%d, %d]", mtu,
+                               MIN_MTU, MAX_MTU);
+                       goto free_stats;
+               }
 
                /* TODO: size buffers correctly in this case. */
                if (dev->mtu > ETH_DATA_LEN)
@@ -2047,6 +2067,7 @@ static struct virtio_driver virtio_net_driver = {
        .driver.name =  KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table =     id_table,
+       .validate =     virtnet_validate,
        .probe =        virtnet_probe,
        .remove =       virtnet_remove,
        .config_changed = virtnet_config_changed,