[PATCH] spapr.c: check bus != NULL in spapr_get_fw_dev_path()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

spapr_get_fw_dev_path() is an impl of
FWPathProviderClass::get_dev_path(). This interface is used by
hw/core/qdev-fw.c via fw_path_provider_try_get_dev_path() in two
functions:

- static char *qdev_get_fw_dev_path_from_handler(), which is used only in
qdev_get_fw_dev_path_helper() and it's guarded by "if (dev &&
dev->parent_bus)";

- char *qdev_get_own_fw_dev_path_from_handler(), which is used in
softmmu/bootdevice.c in get_boot_device_path() like this:

    if (dev) {
        d = qdev_get_own_fw_dev_path_from_handler(dev->parent_bus, dev);

This means that, when called via softmmu/bootdevice.c, there's no check
of 'dev->parent_bus' being not NULL. The result is that the "BusState
*bus" arg of spapr_get_fw_dev_path() can potentially be NULL and if, at
the same time, "SCSIDevice *d" is not NULL, we'll hit this line:

    void *spapr = CAST(void, bus->parent, "spapr-vscsi");

And we'll SIGINT because 'bus' is NULL and we're accessing bus->parent.

Adding a simple 'bus != NULL' check to guard the instances where we
access 'bus->parent' can avoid this altogether.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 hw/ppc/spapr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 72f5dce751..3d6ec309dd 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3053,7 +3053,7 @@ static char *spapr_get_fw_dev_path(FWPathProvider *p, BusState *bus,
     VHostSCSICommon *vsc = CAST(VHostSCSICommon, dev, TYPE_VHOST_SCSI_COMMON);
     PCIDevice *pcidev = CAST(PCIDevice, dev, TYPE_PCI_DEVICE);
 
-    if (d) {
+    if (d && bus) {
         void *spapr = CAST(void, bus->parent, "spapr-vscsi");
         VirtIOSCSI *virtio = CAST(VirtIOSCSI, bus->parent, TYPE_VIRTIO_SCSI);
         USBDevice *usb = CAST(USBDevice, bus->parent, TYPE_USB_DEVICE);
-- 
2.34.1