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virtio_balloon: leak_balloon(): only tell host if we got pages deflated

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balloon_page_dequeue() 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.

This bug was introduced in e2250429.

Signed-off-by: Luiz Capitulino <[email protected]>
Acked-by: Rafael Aquini <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
Cc: [email protected] # 3.9
This commit is contained in:
Luiz Capitulino 2013-07-02 15:35:13 +09:30 • committed by Rusty Russell
commit 8c6bab4f38
1 changed files with 2 additions and 1 deletions
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3
drivers/virtio/virtio_balloon.c
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@ -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);
}