[PATCH] hw/net/virtio-net.c: fix crash in iov_copy()

[Dmitry Frolov]

A crash found while fuzzing device virtio-net-socket-check-used.
Assertion "offset == 0" in iov_copy() fails if less than guest_hdr_len bytes
were transmited.

Signed-off-by: Dmitry Frolov <fro...@swemel.ru>
---
 hw/net/virtio-net.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 24e5e7d347..603b80a50a 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2783,6 +2783,12 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
          */
         assert(n->host_hdr_len <= n->guest_hdr_len);
         if (n->host_hdr_len != n->guest_hdr_len) {
+            if (iov_size(out_sg, out_num) < n->guest_hdr_len) {
+                virtio_error(vdev, "virtio-net header is invalid");
+                virtqueue_detach_element(q->tx_vq, elem, 0);
+                g_free(elem);
+                return -EINVAL;
+            }
             unsigned sg_num = iov_copy(sg, ARRAY_SIZE(sg),
                                        out_sg, out_num,
                                        0, n->host_hdr_len);
-- 
2.43.0