On Tue, Jun 22, 2021 at 6:11 PM Stefan Hajnoczi [off-list ref] wrote:

On Thu, Jun 17, 2021 at 01:10:04PM +0800, Xie Yongji wrote:

quoted

This ensures that we will not use an invalid block size
in config space (might come from an untrusted device).

Signed-off-by: Xie Yongji <redacted>
---
 drivers/block/virtio_blk.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b9fa3ef5b57c..bbdae989f1ea 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c

@@ -696,6 +696,28 @@ static const struct blk_mq_ops virtio_mq_ops = {
 static unsigned int virtblk_queue_depth;
 module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);

+static int virtblk_validate(struct virtio_device *vdev)
+{
+     u32 blk_size;
+
+     if (!vdev->config->get) {
+             dev_err(&vdev->dev, "%s failure: config access disabled\n",
+                     __func__);
+             return -EINVAL;
+     }
+
+     if (!virtio_has_feature(vdev, VIRTIO_BLK_F_BLK_SIZE))
+             return 0;
+
+     blk_size = virtio_cread32(vdev,
+                     offsetof(struct virtio_blk_config, blk_size));
+
+     if (blk_size < SECTOR_SIZE || blk_size > PAGE_SIZE)
+             __virtio_clear_bit(vdev, VIRTIO_BLK_F_BLK_SIZE);
+
+     return 0;
+}

I saw Michael asked for .validate() in v2. I would prefer to keep
everything in virtblk_probe() instead of adding .validate() because:

- There is a race condition that an untrusted device can exploit since
  virtblk_probe() fetches the value again.

Good point! I agree that it's better to add the validation in virtblk_probe().

Thanks,
Yongji