Reproducer from https://gitlab.com/qemu-project/qemu/-/issues/1451 creates small packet (1 segment, len=10 == n->guest_hdr_len), destroys queue.
"if (n->host_hdr_len != n->guest_hdr_len)" is triggered. There is nothing after guest header, if body creates zero length/zero segment packet. qemu_sendv_packet_async() tries to send it. Packet is discarded inside net_slirp_receive() which returns number of sent bytes which is 0. 0 is propagated upwards and is interpreted as "zero bytes has been sent" which is terrible because queue is being destroyed, nobody is waiting for TX to complete, TX complete hook is _not_ called and assert(async_tx.elem) is eventually triggered. The fix is to discard such phantom packets in virtio_net_flush_tx(). Signed-off-by: Alexey Dobriyan <adobri...@yandex-team.ru> --- hw/net/virtio-net.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 58014a92ad..e156f1d78c 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -2765,18 +2765,14 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) out_sg = elem->out_sg; if (out_num < 1) { virtio_error(vdev, "virtio-net header not in first element"); - virtqueue_detach_element(q->tx_vq, elem, 0); - g_free(elem); - return -EINVAL; + goto detach; } if (n->has_vnet_hdr) { 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); - g_free(elem); - return -EINVAL; + goto detach; } if (n->needs_vnet_hdr_swap) { virtio_net_hdr_swap(vdev, (void *) &vhdr); @@ -2807,6 +2803,11 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) n->guest_hdr_len, -1); out_num = sg_num; out_sg = sg; + + if (out_num < 1) { + virtio_error(vdev, "virtio-net nothing to send"); + goto detach; + } } ret = qemu_sendv_packet_async(qemu_get_subqueue(n->nic, queue_index), @@ -2827,6 +2828,11 @@ drop: } } return num_packets; + +detach: + virtqueue_detach_element(q->tx_vq, elem, 0); + g_free(elem); + return -EINVAL; } static void virtio_net_tx_timer(void *opaque); -- 2.43.0