Re: [PATCH] hw/virtio/virtio-pci: add defensive check for vector_irqfd

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

On Thu, Aug 14, 2025 at 02:08:08PM +0300, gerben@altlinux.org wrote:
> From: Denis Rastyogin <gerben@altlinux.org>
> 
> Add a NULL check for proxy->vector_irqfd in
> virtio_pci_one_vector_unmask() before taking the irqfd path.
> This prevents potential access to uninitialized state if
> vector_irqfd is absent.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Reported-by: Alexey Appolonov <alexey@altlinux.org>
> Signed-off-by: Denis Rastyogin <gerben@altlinux.org>


I don't really understand what this description means. defensive against
what?  found in what sense? what is the uninitialized state accessed?
when is the potential for this access?


> ---
>  hw/virtio/virtio-pci.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 767216d795..07904f6f9b 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1015,7 +1015,11 @@ static int virtio_pci_one_vector_unmask(VirtIOPCIProxy *proxy,
>              event_notifier_set(n);
>          }
>      } else {
> -        ret = kvm_virtio_pci_irqfd_use(proxy, n, vector);
> +        if (proxy->vector_irqfd) {
> +            ret = kvm_virtio_pci_irqfd_use(proxy, n, vector);
> +        } else {
> +            ret = -EFAULT;
> +        }
>      }
>      return ret;
>  }
> -- 
> 2.42.2