Re: [PATCH] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

[Philippe Mathieu-Daudé]

On 3/7/23 18:39, Avihai Horon wrote:
> vfio_realize() has the following flow:
> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
> 2. msix_early_setup().
> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
>
> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
> allocated.
>
> In this case, vfio_bars_finalize() is called as part of the error flow
> to free the bars' resources. However, vfio_bars_finalize() calls
> object_unparent() for VFIOBAR->mr unconditionally and thus we get a null
> pointer dereference.
>
> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().
>
> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
>   hw/vfio/pci.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ab6645ba60..95e077082b 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1752,7 +1752,7 @@ static void vfio_bars_finalize(VFIOPCIDevice *vdev)
>   
>           vfio_bar_quirk_finalize(vdev, i);
>           vfio_region_finalize(&bar->region);
> -        if (bar->size) {
> +        if (bar->size && bar->mr) {
>               object_unparent(OBJECT(bar->mr));
>               g_free(bar->mr);
>           }

What about:

            if (bar->mr) {
                assert(bar->size);
                object_unparent(OBJECT(bar->mr));
                g_free(bar->mr);
                bar->mr = NULL;
            }

?