[PATCH v2] virtio_balloon: leak_balloon(): only tell host if we gotpages deflated

From: Luiz Capitulino
Date: Wed Jun 05 2013 - 21:19:05 EST

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 <lcapitulino@xxxxxxxxxx>
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>

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);
release_pages_by_pfn(vb->pfns, vb->num_pfns);

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