Re: [PATCH v5 04/14] vfio/migration: Fix NULL pointer dereference bug

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Avihai Horon (avihaih@nvidia.com) wrote:
> As part of its error flow, vfio_vmstate_change() accesses
> MigrationState->to_dst_file without any checks. This can cause a NULL
> pointer dereference if the error flow is taken and
> MigrationState->to_dst_file is not set.
> 
> For example, this can happen if VM is started or stopped not during
> migration and vfio_vmstate_change() error flow is taken, as
> MigrationState->to_dst_file is not set at that time.
> 
> Fix it by checking that MigrationState->to_dst_file is set before using
> it.
> 
> Fixes: 02a7e71b1e5b ("vfio: Add VM state change handler to know state of VM")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> Reviewed-by: Juan Quintela <quintela@redhat.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

It might be worth posting this patch separately since it's a simple fix
and should go in sooner.

Dave

> ---
>  hw/vfio/migration.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index e1413ac90c..09fe7c1de2 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -743,7 +743,9 @@ static void vfio_vmstate_change(void *opaque, bool running, RunState state)
>           */
>          error_report("%s: Failed to set device state 0x%x", vbasedev->name,
>                       (migration->device_state & mask) | value);
> -        qemu_file_set_error(migrate_get_current()->to_dst_file, ret);
> +        if (migrate_get_current()->to_dst_file) {
> +            qemu_file_set_error(migrate_get_current()->to_dst_file, ret);
> +        }
>      }
>      vbasedev->migration->vm_running = running;
>      trace_vfio_vmstate_change(vbasedev->name, running, RunState_str(state),
> -- 
> 2.26.3
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK