[Qemu-devel] [PATCH v2] virtio: add check for descriptor's mapped address

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

virtio back end uses set of buffers to facilitate I/O operations.
If its size is too large, 'cpu_physical_memory_map' could return
a null address. This would result in a null dereference while
un-mapping descriptors. Add check to avoid it.

Reported-by: Qinghao Tang <luodalongde@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/virtio/virtio.c | 5 +++++
 1 file changed, 5 insertions(+)

Update per:
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg03889.html

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 15ee3a7..311dd0b 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -472,6 +472,11 @@ static void virtqueue_map_desc(unsigned int *p_num_sg, hwaddr *addr, struct iove
         }
 
         iov[num_sg].iov_base = cpu_physical_memory_map(pa, &len, is_write);
+        if (!iov[num_sg].iov_base) {
+            error_report("virtio: bogus descriptor or out of resources");
+            exit(EXIT_FAILURE);
+        }
+
         iov[num_sg].iov_len = len;
         addr[num_sg] = pa;
 
-- 
2.5.5