scsi: scsi_bus_legacy_handle_cmdline() can fail, fix callers

None of its callers checks for failure.  scsi_hot_add() can crash
because of that:

(qemu) drive_add 4 if=scsi,format=host_device,file=/dev/sg1
scsi-generic: scsi generic interface too old
Segmentation fault (core dumped)

Fix all callers, not just scsi_hot_add().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/esp.c

@@ -679,8 +679,7 @@ static int esp_init1(SysBusDevice *dev)
     qdev_init_gpio_in(&dev->qdev, parent_esp_reset, 1);
 
     scsi_bus_new(&s->bus, &dev->qdev, 0, ESP_MAX_DEVS, esp_command_complete);
-    scsi_bus_legacy_handle_cmdline(&s->bus);
-    return 0;
+    return scsi_bus_legacy_handle_cmdline(&s->bus);
 }
 
 static SysBusDeviceInfo esp_info = {

hw/lsi53c895a.c

@@ -2176,7 +2176,7 @@ static int lsi_scsi_init(PCIDevice *dev)
 
     scsi_bus_new(&s->bus, &dev->qdev, 1, LSI_MAX_DEVS, lsi_command_complete);
     if (!dev->qdev.hotplugged) {
-        scsi_bus_legacy_handle_cmdline(&s->bus);
+        return scsi_bus_legacy_handle_cmdline(&s->bus);
     }
     return 0;
 }

hw/pci-hotplug.c

@@ -90,6 +90,9 @@ static int scsi_hot_add(Monitor *mon, DeviceState *adapter,
      */
     dinfo->unit = qemu_opt_get_number(dinfo->opts, "unit", -1);
     scsidev = scsi_bus_legacy_add_drive(scsibus, dinfo, dinfo->unit);
+    if (!scsidev) {
+        return -1;
+    }
     dinfo->unit = scsidev->id;
 
     if (printinfo)

hw/scsi-bus.c

@@ -83,7 +83,6 @@ void scsi_qdev_register(SCSIDeviceInfo *info)
 }
 
 /* handle legacy '-drive if=scsi,...' cmd line args */
-/* FIXME callers should check for failure, but don't */
 SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, DriveInfo *dinfo, int unit)
 {
     const char *driver;
@@ -98,18 +97,22 @@ SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, DriveInfo *dinfo, int unit)
     return DO_UPCAST(SCSIDevice, qdev, dev);
 }
 
-void scsi_bus_legacy_handle_cmdline(SCSIBus *bus)
+int scsi_bus_legacy_handle_cmdline(SCSIBus *bus)
 {
     DriveInfo *dinfo;
-    int unit;
+    int res = 0, unit;
 
     for (unit = 0; unit < MAX_SCSI_DEVS; unit++) {
         dinfo = drive_get(IF_SCSI, bus->busnr, unit);
         if (dinfo == NULL) {
             continue;
         }
-        scsi_bus_legacy_add_drive(bus, dinfo, unit);
+        if (!scsi_bus_legacy_add_drive(bus, dinfo, unit)) {
+            res = -1;
+            break;
+        }
     }
+    return res;
 }
 
 void scsi_dev_clear_sense(SCSIDevice *dev)

hw/scsi.h

@@ -98,7 +98,7 @@ static inline SCSIBus *scsi_bus_from_device(SCSIDevice *d)
 }
 
 SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, DriveInfo *dinfo, int unit);
-void scsi_bus_legacy_handle_cmdline(SCSIBus *bus);
+int scsi_bus_legacy_handle_cmdline(SCSIBus *bus);
 
 void scsi_dev_clear_sense(SCSIDevice *dev);
 void scsi_dev_set_sense(SCSIDevice *dev, uint8_t key);

hw/usb-msd.c

@@ -531,6 +531,9 @@ static int usb_msd_initfn(USBDevice *dev)
     s->dev.speed = USB_SPEED_FULL;
     scsi_bus_new(&s->bus, &s->dev.qdev, 0, 1, usb_msd_command_complete);
     s->scsi_dev = scsi_bus_legacy_add_drive(&s->bus, s->conf.dinfo, 0);
+    if (!s->scsi_dev) {
+        return -1;
+    }
     s->bus.qbus.allow_hotplug = 0;
     usb_msd_handle_reset(dev);