[PATCH v3] vhost: avoid potential null pointer access

[Li Feng]

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 <fen...@smartx.com>
---
v2 -> v3:
- Also fix the rte_vhost_vring_call_nonblock.

v1 -> v2:
- Fix rebase error.



 lib/vhost/vhost.c | 14 ++++++++------
 lib/vhost/vhost.h | 12 ++++++++++--
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index eb6309b681..46f3391167 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
@@ -1356,6 +1357,7 @@ rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx)
 {
        struct virtio_net *dev;
        struct vhost_virtqueue *vq;
+       int ret = 0;

        dev = get_device(vid);
        if (!dev)
@@ -1372,13 +1374,13 @@ rte_vhost_vring_call_nonblock(int vid, uint16_t 
vring_idx)
                return -EAGAIN;

        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;
 }

 uint16_t
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