On Tue, Oct 21, 2025 at 07:07:56PM +0800, Cong Zhang wrote:
> The vblk->vqs releases during freeze. If resume fails before vblk->vqs
> is allocated, later freeze/remove may attempt to free vqs again.
> Set vblk->vqs to NULL after freeing to avoid double free.
>
> Signed-off-by: Cong Zhang <[email protected]>
> ---
> The patch fixes a double free issue that occurs in virtio_blk during
> freeze/resume.
> The issue is caused by:
> 1. During the first freeze, vblk->vqs is freed but pointer is not set to
> NULL.
> 2. Virtio block device fails before vblk->vqs is allocated during resume.
> 3. During the next freeze, vblk->vqs gets freed again, causing the
> double free crash.
this part I don't get. if restore fails, how can freeze be called
again?
> ---
> drivers/block/virtio_blk.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index
> f061420dfb10c40b21765b173fab7046aa447506..746795066d7f56a01c9a9c0344d24f9fa06841eb
> 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1026,8 +1026,13 @@ static int init_vq(struct virtio_blk *vblk)
> out:
> kfree(vqs);
> kfree(vqs_info);
> - if (err)
> + if (err) {
> kfree(vblk->vqs);
> + /*
> + * Set to NULL to prevent freeing vqs again during freezing.
> + */
> + vblk->vqs = NULL;
> + }
> return err;
> }
>
> @@ -1598,6 +1603,12 @@ static int virtblk_freeze_priv(struct virtio_device
> *vdev)
>
> vdev->config->del_vqs(vdev);
> kfree(vblk->vqs);
> + /*
> + * Set to NULL to prevent freeing vqs again after a failed vqs
> + * allocation during resume. Note that kfree() already handles NULL
> + * pointers safely.
> + */
> + vblk->vqs = NULL;
>
> return 0;
> }
>
> ---
> base-commit: 8e2755d7779a95dd61d8997ebce33ff8b1efd3fb
> change-id: 20250926-virtio_double_free-7ab880d82a17
>
> Best regards,
> --
> Cong Zhang <[email protected]>
