| Message ID | 1456830843-24835-1-git-send-email-lprosek@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 01/03/2016 12:14, Ladi Prosek wrote: > 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. > > Signed-off-by: Ladi Prosek <lprosek@redhat.com> > --- > 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; > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> There seem to be no other instances of the bug. Paolo
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;
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. Signed-off-by: Ladi Prosek <lprosek@redhat.com> --- hw/virtio/virtio-balloon.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)