From: Luiz Capitulino Date: Tue, 2 Jul 2013 06:05:13 +0000 (+0930) Subject: virtio_balloon: leak_balloon(): only tell host if we got pages deflated X-Git-Tag: firefly_0821_release~176^2~5732^2~8 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=8c6bab4f3874d31804a00782c48a8f244a0d3cc0;p=firefly-linux-kernel-4.4.55.git virtio_balloon: leak_balloon(): only tell host if we got pages deflated 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 Acked-by: Rafael Aquini Signed-off-by: Andrew Morton Signed-off-by: Rusty Russell Cc: stable@kernel.org # 3.9 --- diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index bd3ae324a1a2..71af7b5abe01 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); }