The balloon_page_dequeue() function can return NULL. If it does for
the first page being freed, then leak_balloon() will create a
scatter list with len=0. Which in turn seems to generate an invalid
virtio request.
I didn't get this in practice, I found it by code review. On the other
hand, such an invalid virtio request will cause errors in QEMU and
fill_balloon() also performs the same check implemented by this commit.
Signed-off-by: Luiz Capitulino <[email protected]>
Acked-by: Rafael Aquini <[email protected]>
---
o v2
- Improve changelog
drivers/virtio/virtio_balloon.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index bd3ae32..71af7b5 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
* virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
* is true, we *have* to do it in this order
*/
- tell_host(vb, vb->deflate_vq);
+ if (vb->num_pfns != 0)
+ tell_host(vb, vb->deflate_vq);
mutex_unlock(&vb->balloon_lock);
release_pages_by_pfn(vb->pfns, vb->num_pfns);
}
--
1.8.1.4
On Wed, Jun 05, 2013 at 09:18:37PM -0400, Luiz Capitulino wrote:
> The balloon_page_dequeue() function can return NULL. If it does for
> the first page being freed, then leak_balloon() will create a
> scatter list with len=0. Which in turn seems to generate an invalid
> virtio request.
>
> I didn't get this in practice, I found it by code review. On the other
> hand, such an invalid virtio request will cause errors in QEMU and
> fill_balloon() also performs the same check implemented by this commit.
>
> Signed-off-by: Luiz Capitulino <[email protected]>
> Acked-by: Rafael Aquini <[email protected]>
> ---
>
> o v2
>
> - Improve changelog
>
> drivers/virtio/virtio_balloon.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index bd3ae32..71af7b5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> * is true, we *have* to do it in this order
> */
> - tell_host(vb, vb->deflate_vq);
Luiz, sorry for not being clearer before. I was referring to add a commentary on
code, to explain in short words why we should not get rid of this check point.
> + if (vb->num_pfns != 0)
> + tell_host(vb, vb->deflate_vq);
> mutex_unlock(&vb->balloon_lock);
If the comment is regarded as unnecessary, then just ignore my suggestion. I'm
OK with your patch. :)
Cheers!
-- Rafael
On Thu, 6 Jun 2013 11:13:58 -0300
Rafael Aquini <[email protected]> wrote:
> On Wed, Jun 05, 2013 at 09:18:37PM -0400, Luiz Capitulino wrote:
> > The balloon_page_dequeue() function can return NULL. If it does for
> > the first page being freed, then leak_balloon() will create a
> > scatter list with len=0. Which in turn seems to generate an invalid
> > virtio request.
> >
> > I didn't get this in practice, I found it by code review. On the other
> > hand, such an invalid virtio request will cause errors in QEMU and
> > fill_balloon() also performs the same check implemented by this commit.
> >
> > Signed-off-by: Luiz Capitulino <[email protected]>
> > Acked-by: Rafael Aquini <[email protected]>
> > ---
> >
> > o v2
> >
> > - Improve changelog
> >
> > drivers/virtio/virtio_balloon.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index bd3ae32..71af7b5 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> > * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> > * is true, we *have* to do it in this order
> > */
> > - tell_host(vb, vb->deflate_vq);
>
> Luiz, sorry for not being clearer before. I was referring to add a commentary on
> code, to explain in short words why we should not get rid of this check point.
Oh.
> > + if (vb->num_pfns != 0)
> > + tell_host(vb, vb->deflate_vq);
> > mutex_unlock(&vb->balloon_lock);
>
> If the comment is regarded as unnecessary, then just ignore my suggestion. I'm
> OK with your patch. :)
IMHO, the code is clear enough.
On Wed, 5 Jun 2013 21:18:37 -0400
Luiz Capitulino <[email protected]> wrote:
> The balloon_page_dequeue() function can return NULL. If it does for
> the first page being freed, then leak_balloon() will create a
> scatter list with len=0. Which in turn seems to generate an invalid
> virtio request.
>
> I didn't get this in practice, I found it by code review. On the other
> hand, such an invalid virtio request will cause errors in QEMU and
> fill_balloon() also performs the same check implemented by this commit.
>
> Signed-off-by: Luiz Capitulino <[email protected]>
> Acked-by: Rafael Aquini <[email protected]>
Andrew, can you pick this one?
> ---
>
> o v2
>
> - Improve changelog
>
> drivers/virtio/virtio_balloon.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index bd3ae32..71af7b5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> * is true, we *have* to do it in this order
> */
> - tell_host(vb, vb->deflate_vq);
> + if (vb->num_pfns != 0)
> + tell_host(vb, vb->deflate_vq);
> mutex_unlock(&vb->balloon_lock);
> release_pages_by_pfn(vb->pfns, vb->num_pfns);
> }