Re: [Qemu-devel] [PATCH v2] s390: avoid potential null dereference in s390_pcihost_unplug()

[Cornelia Huck <cohuck@redhat.com>]

On Thu,  3 Jan 2019 07:16:12 -0800
Li Qiang <liq3ea@163.com> wrote:

> When getting the 'pbdev', the if...else has no default branch.
> From Coverity, the 'pbdev' maybe null when the 'dev' is not
> the TYPE_PCI_BRIDGE/TYPE_PCI_DEVICE/TYPE_S390_PCI_DEVICE.
> This patch adds a default branch for device plug and unplug.
> 
> Spotted by Coverity: CID 1398593
> 
> Signed-off-by: Li Qiang <liq3ea@163.com>
> ---
> Adds a default branch for device plug per Cornelia's review.
> 
>  hw/s390x/s390-pci-bus.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> index 15759b6514..fe48a36ff6 100644
> --- a/hw/s390x/s390-pci-bus.c
> +++ b/hw/s390x/s390-pci-bus.c
> @@ -912,6 +912,9 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>          pbdev->fh = pbdev->idx;
>          QTAILQ_INSERT_TAIL(&s->zpci_devs, pbdev, link);
>          g_hash_table_insert(s->zpci_table, &pbdev->idx, pbdev);
> +    } else {
> +        error_setg(errp, "s390: device plug request for not supported device"
> +                   " type: %s", object_get_typename(OBJECT(dev)));

Maybe make this "s390/pci: plugging device type <%s> is not supported"?

>      }
>  }
>  
> @@ -956,6 +959,10 @@ static void s390_pcihost_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_S390_PCI_DEVICE)) {
>          pbdev = S390_PCI_DEVICE(dev);
>          pci_dev = pbdev->pdev;
> +    } else {
> +        error_setg(errp, "s390: device unplug request for not supported device"
> +                   " type: %s", object_get_typename(OBJECT(dev)));

Halil has a point when he suggests an assert here. If we fence the
device type in the plug function, I can't think of a way we would end
up here.

> +        return;
>      }
>  
>      switch (pbdev->state) {