[PATCH v2] vhost: avoid potential null pointer access

[Li Feng <fengli@smartx.com>]

If the user calls rte_vhost_vring_call() on a ring that has been
invalidated, we will encounter SEGV.

We should check the pointer firstly before accessing it.

Signed-off-by: Li Feng <fengli@smartx.com>
---
 lib/vhost/vhost.c |  7 ++++---
 lib/vhost/vhost.h | 12 ++++++++++--
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index eb6309b681..3af0307cd6 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -1327,6 +1327,7 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
 {
 	struct virtio_net *dev;
 	struct vhost_virtqueue *vq;
+	int ret = 0;
 
 	dev = get_device(vid);
 	if (!dev)
@@ -1342,13 +1343,13 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
 	rte_rwlock_read_lock(&vq->access_lock);
 
 	if (vq_is_packed(dev))
-		vhost_vring_call_packed(dev, vq);
+		ret = vhost_vring_call_packed(dev, vq);
 	else
-		vhost_vring_call_split(dev, vq);
+		ret = vhost_vring_call_split(dev, vq);
 
 	rte_rwlock_read_unlock(&vq->access_lock);
 
-	return 0;
+	return ret;
 }
 
 int
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 9723429b1c..4c09c2ef0e 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -930,12 +930,15 @@ vhost_vring_inject_irq(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		dev->notify_ops->guest_notified(dev->vid);
 }
 
-static __rte_always_inline void
+static __rte_always_inline int
 vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
 	/* Flush used->idx update before we read avail->flags. */
 	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);
 
+	if (!vq->avail || !vq->used)
+		return -1;
+
 	/* Don't kick guest if we don't reach index specified by guest. */
 	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
 		uint16_t old = vq->signalled_used;
@@ -957,9 +960,10 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
 			vhost_vring_inject_irq(dev, vq);
 	}
+	return 0;
 }
 
-static __rte_always_inline void
+static __rte_always_inline int
 vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
 	uint16_t old, new, off, off_wrap;
@@ -968,6 +972,9 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
 	/* Flush used desc update. */
 	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);
 
+	if (!vq->driver_event)
+		return -1;
+
 	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
 		if (vq->driver_event->flags !=
 				VRING_EVENT_F_DISABLE)
@@ -1008,6 +1015,7 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
 kick:
 	if (kick)
 		vhost_vring_inject_irq(dev, vq);
+	return 0;
 }
 
 static __rte_always_inline void
-- 
2.41.0