[RFC PATCH 4/7] virtio_ring: secure handling of mapping errors

[Jason Wang]

We should not depend on the DMA address, length and flag of descriptor
table since they could be wrote with arbitrary value by the device. So
this patch switches to use the stored one in desc_extra.

Note that the indirect descriptors are fine since they are read-only
streaming mappings.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0cdd965dba58..5509c2643fb1 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1213,13 +1213,16 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 unmap_release:
 	err_idx = i;
 	i = head;
+	curr = vq->free_head;
 
 	vq->packed.avail_used_flags = avail_used_flags;
 
 	for (n = 0; n < total_sg; n++) {
 		if (i == err_idx)
 			break;
-		vring_unmap_desc_packed(vq, &desc[i]);
+		vring_unmap_state_packed(vq,
+					 &vq->packed.desc_extra[curr]);
+		curr = vq->packed.desc_extra[curr].next;
 		i++;
 		if (i >= vq->packed.vring.num)
 			i = 0;
-- 
2.25.1