On Tue, Jul 28, 2026 at 6:47 PM Ankur Saini <[email protected]> wrote: > > A control request shorter than virtio_gpu_ctrl_hdr can leave cmd_hdr > partially initialized. If the supplied bytes set the fence flag, stale > fence metadata may later be returned to the guest. > > Validate the common header length before dispatch. Clear cmd_hdr and > complete malformed requests with ERR_INVALID_PARAMETER so stale fields > cannot reach the response. > > Fixes: CVE-2026-18054 > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4094 > Reported-by: Ankur Saini <[email protected]> > Signed-off-by: Ankur Saini <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]> > --- > A control request shorter than virtio_gpu_ctrl_hdr can leave cmd_hdr > partially initialized. If the supplied bytes set the fence flag, stale > fence metadata may later be returned to the guest. > > Validate the common header length before dispatch. Clear cmd_hdr and > complete malformed requests with ERR_INVALID_PARAMETER so stale fields > cannot reach the response. > --- > hw/display/virtio-gpu.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c > index 4d46a4eb10..15a845eff6 100644 > --- a/hw/display/virtio-gpu.c > +++ b/hw/display/virtio-gpu.c > @@ -1105,8 +1105,14 @@ void virtio_gpu_process_cmdq(VirtIOGPU *g) > break; > } > > - /* process command */ > - vgc->process_cmd(g, cmd); > + if (unlikely(iov_size(cmd->elem.out_sg, cmd->elem.out_num) < > + sizeof(cmd->cmd_hdr))) { > + memset(&cmd->cmd_hdr, 0, sizeof(cmd->cmd_hdr)); > + virtio_gpu_ctrl_response_nodata( > + g, cmd, VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER); > + } else { > + vgc->process_cmd(g, cmd); > + } > > /* command suspended */ > if (!cmd->finished && !(cmd->cmd_hdr.flags & VIRTIO_GPU_FLAG_FENCE)) > { > > --- > base-commit: 299e7557ed15a9a325620698add379a3ce2d1d95 > change-id: 20260728-virtio-gpu-short-header-476aa1dae4f7 > > Best regards, > -- > Ankur Saini <[email protected]> > > -- Marc-André Lureau
