From: Jason Wang <jasowang@redhat.com>

When HASH_REPORT is negotiated, the guest_hdr_len might be larger than
the size of the mergeable rx buffer header. Using
virtio_net_hdr_mrg_rxbuf during the header swap might lead a stack
overflow in this case. Fixing this by using virtio_net_hdr_v1_hash
instead.

Reported-by: Xiao Lei <leixiao.nop@zju.edu.cn>
Cc: Yuri Benditovich <yuri.benditovich@daynix.com>
Cc: qemu-stable@nongnu.org
Cc: Mauro Matteo Cascella <mcascell@redhat.com>
Fixes: CVE-2023-6693
Fixes: e22f0603fb2f ("virtio-net: reference implementation of hash report")
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 2220e8189fb94068dbad333228659fbac819abb0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 06f35ac2d8..412cba4927 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -664,6 +664,11 @@ static void virtio_net_set_mrg_rx_bufs(VirtIONet *n, int mergeable_rx_bufs,
 
     n->mergeable_rx_bufs = mergeable_rx_bufs;
 
+    /*
+     * Note: when extending the vnet header, please make sure to
+     * change the vnet header copying logic in virtio_net_flush_tx()
+     * as well.
+     */
     if (version_1) {
         n->guest_hdr_len = hash_report ?
             sizeof(struct virtio_net_hdr_v1_hash) :
@@ -2630,7 +2635,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
         ssize_t ret;
         unsigned int out_num;
         struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1], *out_sg;
-        struct virtio_net_hdr_mrg_rxbuf mhdr;
+        struct virtio_net_hdr_v1_hash vhdr;
 
         elem = virtqueue_pop(q->tx_vq, sizeof(VirtQueueElement));
         if (!elem) {
@@ -2647,7 +2652,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
         }
 
         if (n->has_vnet_hdr) {
-            if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) <
+            if (iov_to_buf(out_sg, out_num, 0, &vhdr, n->guest_hdr_len) <
                 n->guest_hdr_len) {
                 virtio_error(vdev, "virtio-net header incorrect");
                 virtqueue_detach_element(q->tx_vq, elem, 0);
@@ -2655,8 +2660,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
                 return -EINVAL;
             }
             if (n->needs_vnet_hdr_swap) {
-                virtio_net_hdr_swap(vdev, (void *) &mhdr);
-                sg2[0].iov_base = &mhdr;
+                virtio_net_hdr_swap(vdev, (void *) &vhdr);
+                sg2[0].iov_base = &vhdr;
                 sg2[0].iov_len = n->guest_hdr_len;
                 out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1,
                                    out_sg, out_num,
-- 
2.39.2