Re: [PATCH 3/9] vfio/migration: Fix NULL pointer dereference bug

[Juan Quintela]

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>
> ---
>  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 835608cd23..21e8f9d4d4 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -744,7 +744,9 @@ 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);
> +        }
>      }

Reviewed-by: Juan Quintela <quintela@redhat.com>

I mean that the change is right.

But I am not so sure about using qemu_file_* operations outside of the
migration_thread.  I *think* that everything else that uses qemu_file_*
functions is operating inside the migration_thread, and this one don't
look like it.  Furthermore, a fast look at qemu source, I can't see
anyplace where we setup an error in a vmstate_change.

Later, Juan.

>      vbasedev->migration->vm_running = running;
>      trace_vfio_vmstate_change(vbasedev->name, running, RunState_str(state),