Re: [PATCH] vhost-user-gpu: fix integer overflow in buffer allocation

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jul 10, 2026 at 05:47:19PM +0400, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> A malicious guest can trigger a heap buffer overflow in the
> vhost-user-gpu backend by sending a VIRTIO_GPU_CMD_RESOURCE_CREATE_2D
> with large width and height values (e.g. 65537x65537). The allocation
> size width * height * 4 silently wraps in uint32_t arithmetic,
> resulting in a much smaller allocation than expected. Subsequent
> VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D writes past the heap buffer.
> 
> The in-tree virtio-gpu device (hw/display/virtio-gpu.c) already handles
> this via calc_image_hostmem() with uint64_t arithmetic and an overflow
> check. Apply the same approach to the vhost-user-gpu contrib backend:
> 
> - Add an overflow check in vugbm_buffer_create() rejecting dimensions
>   where width * height * 4 exceeds UINT32_MAX
> - Promote the size arithmetic to uint64_t in mem_alloc_bo() and
>   udmabuf_get_size()
> - Check the return value of vugbm_buffer_create() in
>   vg_resource_create_2d(), which was previously ignored
> 
> Fixes: CVE-2026-15264
> Reported-by: "Vulnerability Report" <vr@darknavy.com>
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3940
> Signed-off-by: Marc-Andre Lureau <marcandre.lureau@redhat.com>
> ---
>  contrib/vhost-user-gpu/vhost-user-gpu.c |  8 +++++++-
>  contrib/vhost-user-gpu/vugbm.c          | 11 +++++++++--
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/contrib/vhost-user-gpu/vhost-user-gpu.c b/contrib/vhost-user-gpu/vhost-user-gpu.c
> index bb41758e345..ee9858c397c 100644
> --- a/contrib/vhost-user-gpu/vhost-user-gpu.c
> +++ b/contrib/vhost-user-gpu/vhost-user-gpu.c
> @@ -388,7 +388,13 @@ vg_resource_create_2d(VuGpu *g,
>          cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
>          return;
>      }
> -    vugbm_buffer_create(&res->buffer, &g->gdev, c2d.width, c2d.height);
> +    if (!vugbm_buffer_create(&res->buffer, &g->gdev, c2d.width, c2d.height)) {
> +        g_critical("%s: buffer creation failed %d %d %d",
> +                   __func__, c2d.resource_id, c2d.width, c2d.height);
> +        g_free(res);
> +        cmd->error = VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY;
> +        return;
> +    }
>      res->image = pixman_image_create_bits(pformat,
>                                            c2d.width,
>                                            c2d.height,
> diff --git a/contrib/vhost-user-gpu/vugbm.c b/contrib/vhost-user-gpu/vugbm.c
> index 503d0a4566f..710d5452977 100644
> --- a/contrib/vhost-user-gpu/vugbm.c
> +++ b/contrib/vhost-user-gpu/vugbm.c
> @@ -13,7 +13,7 @@
>  static bool
>  mem_alloc_bo(struct vugbm_buffer *buf)
>  {
> -    buf->mmap = g_malloc(buf->width * buf->height * 4);
> +    buf->mmap = g_malloc((uint64_t)buf->width * buf->height * 4);
>      buf->stride = buf->width * 4;
>      return true;
>  }


I apologise but we are still allocating up to 2Gbytes is that really
sane? Isn't there a limit on these things? Like the size of the screen?

And width * 4 can still wrap around and then will it really behave
correctly?



> @@ -53,7 +53,8 @@ struct udmabuf_create {
>  static size_t
>  udmabuf_get_size(struct vugbm_buffer *buf)
>  {
> -    return ROUND_UP(buf->width * buf->height * 4, qemu_real_host_page_size());
> +    return ROUND_UP((uint64_t)buf->width * buf->height * 4,
> +                    qemu_real_host_page_size());
>  }
>  
>  static bool
> @@ -293,6 +294,12 @@ bool
>  vugbm_buffer_create(struct vugbm_buffer *buffer, struct vugbm_device *dev,
>                      uint32_t width, uint32_t height)
>  {
> +    uint64_t size = (uint64_t)width * height * 4;
> +    if (size > UINT32_MAX) {
> +        g_warning("buffer dimensions too large: %ux%u", width, height);
> +        return false;
> +    }
> +
>      buffer->dev = dev;
>      buffer->width = width;
>      buffer->height = height;
> -- 
> 2.55.0