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balloon: fix segfault and harden the stats queue 

The segfault here is triggered by the driver notifying the stats queue
twice after adding a buffer to it. This effectively resets stats_vq_elem
back to NULL and QEMU crashes on the next stats timer tick in
balloon_stats_poll_cb.

This is a regression introduced in 51b19ebe43, although admittedly
the device assumed too much about the stats queue protocol even before
that commit. This commit adds a few more checks and ensures that the one
stats buffer gets deallocated on device reset.

Cc: qemu-stable@nongnu.org
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Ladi Prosek 2016-03-01 12:14:03 +01:00 committed by Michael S. Tsirkin
parent f203549108
commit 4eae2a657d
1 changed files with 22 additions and 2 deletions
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24
hw/virtio/virtio-balloon.c
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@ -101,7 +101,7 @@ static void balloon_stats_poll_cb(void *opaque)
VirtIOBalloon *s = opaque;
VirtIODevice *vdev = VIRTIO_DEVICE(s);
if (!balloon_stats_supported(s)) {
if (s->stats_vq_elem == NULL || !balloon_stats_supported(s)) {
/* re-schedule */
balloon_stats_change_timer(s, s->stats_poll_interval);
return;
@ -258,11 +258,20 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
size_t offset = 0;
qemu_timeval tv;
s->stats_vq_elem = elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
if (!elem) {
goto out;
}
if (s->stats_vq_elem != NULL) {
/* This should never happen if the driver follows the spec. */
virtqueue_push(vq, s->stats_vq_elem, 0);
virtio_notify(vdev, vq);
g_free(s->stats_vq_elem);
}
s->stats_vq_elem = elem;
/* Initialize the stats to get rid of any stale values. This is only
* needed to handle the case where a guest supports fewer stats than it
* used to (ie. it has booted into an old kernel).
@ -458,6 +467,16 @@ static void virtio_balloon_device_unrealize(DeviceState *dev, Error **errp)
virtio_cleanup(vdev);
}
static void virtio_balloon_device_reset(VirtIODevice *vdev)
{
VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
if (s->stats_vq_elem != NULL) {
g_free(s->stats_vq_elem);
s->stats_vq_elem = NULL;
}
}
static void virtio_balloon_instance_init(Object *obj)
{
VirtIOBalloon *s = VIRTIO_BALLOON(obj);
@ -486,6 +505,7 @@ static void virtio_balloon_class_init(ObjectClass *klass, void *data)
set_bit(DEVICE_CATEGORY_MISC, dc->categories);
vdc->realize = virtio_balloon_device_realize;
vdc->unrealize = virtio_balloon_device_unrealize;
vdc->reset = virtio_balloon_device_reset;
vdc->get_config = virtio_balloon_get_config;
vdc->set_config = virtio_balloon_set_config;
vdc->get_features = virtio_balloon_get_features;