[Qemu-devel] [PATCH] hw/virtio/virtio-balloon: zero-initialize the virtio_balloon_config struct

[Peter Maydell <peter.maydell@linaro.org>]

In virtio_balloon_get_config() we initialize a struct virtio_balloon_config
which we then copy to guest memory. However, the local variable is not
zero initialized. This works OK at the moment because we initialize
all the fields in it; however an upcoming kernel header change will
add some new fields. If we don't zero out the whole struct then we
will start leaking a small amount of the contents of QEMU's stack
to the guest as soon as we update linux-headers/ to a set of headers
that includes the new fields.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
It looks like none of the other virtio devices have this bug.
Tested with "make check" only.
As the commit message notes, must go in before our next headers update.
---
 hw/virtio/virtio-balloon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 1728e4f83af..a12677d4d5b 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -311,7 +311,7 @@ out:
 static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
 {
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
-    struct virtio_balloon_config config;
+    struct virtio_balloon_config config = {};
 
     config.num_pages = cpu_to_le32(dev->num_pages);
     config.actual = cpu_to_le32(dev->actual);
-- 
2.20.1