[Qemu-stable] [PATCH 5/5] virtio-net: unbreak any layout

[Jason Wang]

Commit 032a74a1c0fcdd5fd1c69e56126b4c857ee36611
("virtio-net: byteswap virtio-net header") breaks any layout by
requiring out_sg[0].iov_len >= n->guest_hdr_len. Fixing this by
copying header to temporary buffer and copying it back after byteswap.

Fixes 032a74a1c0fcdd5fd1c69e56126b4c857ee36611
("virtio-net: byteswap virtio-net header")
Cc: address@hidden
Cc: address@hidden
Signed-off-by: Jason Wang <address@hidden>
---
 hw/net/virtio-net.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index e3c2db3..b42af8f 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1139,10 +1139,11 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
     }
 
     while (virtqueue_pop(q->tx_vq, &elem)) {
-        ssize_t ret, len;
+        ssize_t ret, len, s;
         unsigned int out_num = elem.out_num;
         struct iovec *out_sg = &elem.out_sg[0];
         struct iovec sg[VIRTQUEUE_MAX_SIZE];
+        struct virtio_net_hdr hdr;
 
         if (out_num < 1) {
             error_report("virtio-net header not in first element");
@@ -1150,11 +1151,14 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
         }
 
         if (n->has_vnet_hdr) {
-            if (out_sg[0].iov_len < n->guest_hdr_len) {
+            s = iov_to_buf(out_sg, out_num, 0, &hdr, sizeof(hdr));
+            if (s != sizeof(hdr)) {
                 error_report("virtio-net header incorrect");
                 exit(1);
             }
-            virtio_net_hdr_swap(vdev, (void *) out_sg[0].iov_base);
+            virtio_net_hdr_swap(vdev, (void *) &hdr);
+            s = iov_from_buf(out_sg, out_num, 0, &hdr, sizeof(hdr));
+            assert(s == sizeof(hdr));
         }
 
         /*
-- 
2.1.4