On Tue, Oct 21, 2025 at 8:58 PM Michael S. Tsirkin <[email protected]> wrote:
>
> 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?
For example, could it be triggered by the user?
Thanks
>
> > ---
> > 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]>
>
