[Qemu-devel] [PATCH 2/2] libvhost-user: make vu_queue_empty() safer

[Marc-André Lureau]

Check if vring.avail != null before accessing it.

Fix crashes from callers such a vu_queue_pop() when queue isn't ready.

Fix documentation and return type while at it.

Signed-off-by: Marc-André Lureau <address@hidden>
---
 contrib/libvhost-user/libvhost-user.h | 6 +++---
 contrib/libvhost-user/libvhost-user.c | 8 ++++++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.h 
b/contrib/libvhost-user/libvhost-user.h
index 156b50e989..af02a31ebe 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -327,13 +327,13 @@ void vu_queue_set_notification(VuDev *dev, VuVirtq *vq, 
int enable);
 bool vu_queue_enabled(VuDev *dev, VuVirtq *vq);
 
 /**
- * vu_queue_enabled:
+ * vu_queue_empty:
  * @dev: a VuDev context
  * @vq: a VuVirtq queue
  *
- * Returns: whether the queue is empty.
+ * Returns: true if the queue is empty or not ready.
  */
-int vu_queue_empty(VuDev *dev, VuVirtq *vq);
+bool vu_queue_empty(VuDev *dev, VuVirtq *vq);
 
 /**
  * vu_queue_notify:
diff --git a/contrib/libvhost-user/libvhost-user.c 
b/contrib/libvhost-user/libvhost-user.c
index f9680b6279..b0f15b76e3 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -1125,11 +1125,15 @@ vu_queue_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned 
int in_bytes,
 
 /* Fetch avail_idx from VQ memory only when we really need to know if
  * guest has added some buffers. */
-int
+bool
 vu_queue_empty(VuDev *dev, VuVirtq *vq)
 {
+    if (!vq->vring.avail) {
+        return true;
+    }
+
     if (vq->shadow_avail_idx != vq->last_avail_idx) {
-        return 0;
+        return false;
     }
 
     return vring_avail_idx(vq) == vq->last_avail_idx;
-- 
2.12.0.191.gc5d8de91d