util: Fix for NULL dereference

The device xml parser code does not set "model" while parsing the
following XML:

  <interface type='hostdev'>
    <source>
      <address type='pci' domain='0x0002' bus='0x01' slot='0x00' function='0x2'/>
    </source>
  </interface>

The net->model can be NULL and therefore must be compared using
STREQ_NULLABLE instead of plain STREQ.

Fixes: ac47e4a6 (qemu: replace "def->nets[i]" with "net" and "def->sounds[i]" with "sound")
Fixes: c7fc151e (qemu: assign virtio devices to PCIe slot when appropriate)
Signed-off-by: NRadoslaw Biernacki <radoslaw.biernacki@linaro.org>
Signed-off-by: Ndann frazier <dann.frazier@canonical.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_domain_address.c

@@ -230,10 +230,8 @@ qemuDomainAssignSpaprVIOAddresses(virDomainDefPtr def)
     for (i = 0; i < def->nnets; i++) {
         virDomainNetDefPtr net = def->nets[i];
 
-        if (net->model &&
-            STREQ(net->model, "spapr-vlan")) {
+        if (STREQ_NULLABLE(net->model, "spapr-vlan"))
             net->info.type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_SPAPRVIO;
-        }
 
         if (qemuDomainAssignSpaprVIOAddress(def, &net->info, VIO_ADDR_NET) < 0)
             goto cleanup;
@@ -322,8 +320,7 @@ qemuDomainPrimeVirtioDeviceAddresses(virDomainDefPtr def,
     for (i = 0; i < def->nnets; i++) {
         virDomainNetDefPtr net = def->nets[i];
 
-        if (net->model &&
-            STREQ(net->model, "virtio") &&
+        if (STREQ_NULLABLE(net->model, "virtio") &&
             net->info.type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_NONE) {
             net->info.type = type;
         }
@@ -691,14 +688,14 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev,
          * addresses for other hostdev devices.
          */
         if (net->type == VIR_DOMAIN_NET_TYPE_HOSTDEV ||
-            STREQ(net->model, "usb-net")) {
+            STREQ_NULLABLE(net->model, "usb-net")) {
             return 0;
         }
 
-        if (STREQ(net->model, "virtio"))
+        if (STREQ_NULLABLE(net->model, "virtio"))
             return  virtioFlags;
 
-        if (STREQ(net->model, "e1000e"))
+        if (STREQ_NULLABLE(net->model, "e1000e"))
             return pcieFlags;
 
         return pciFlags;