From 4eae2a657d1ff5ada56eb9b4966eae0eff333b0b Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Tue, 1 Mar 2016 12:14:03 +0100 Subject: [PATCH] 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 51b19ebe4320f3dc, 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 Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- hw/virtio/virtio-balloon.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index e9c30e9..e97d403 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -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; -- 2.7.4