[Qemu-devel] [PATCH 4/5] usb/dev-storage: Fix QMP device_add missing encryption key failure

[Markus Armbruster <armbru@redhat.com>]

When the image is encrypted, QMP device_add creates the device, defers
actually attaching it to when the key becomes available, then returns
an error.  This is wrong.  device_add must either create the device
and succeed, or do nothing and fail.

The bug is in usb_msd_realize_storage().  It posts an error with
qerror_report_err(), and returns success.  Device realization relies
on the return value, and completes.  The QMP monitor, however, relies
on the posted error, and sends it in an error reply.

Reproducer:

    $ qemu-system-x86_64 -nodefaults -display none -usb -qmp stdio -drive if=none,id=foo,file=geheim.qcow2
    {"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major": 2}, "package": ""}, "capabilities": []}}
    { "execute": "qmp_capabilities" }
    {"return": {}}
    { "execute": "device_add", "arguments": { "driver": "usb-storage", "id": "bar", "drive": "foo" } }
    {"error": {"class": "DeviceEncrypted", "desc": "'foo' (geheim.qcow2) is encrypted"}}

Even though we got an error back, the device got created just fine.
To demonstrate, let's unplug it again:

    {"execute":"device_del","arguments": { "id": "bar" } }
    {"timestamp": {"seconds": 1426003440, "microseconds": 237181}, "event": "DEVICE_DELETED", "data": {"path": "/machine/peripheral/bar/bar.0/legacy[0]"}}
    {"timestamp": {"seconds": 1426003440, "microseconds": 238231}, "event": "DEVICE_DELETED", "data": {"device": "bar", "path": "/machine/peripheral/bar"}}
    {"return": {}}

Fix by making usb_msd_realize_storage() fail properly.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/usb/dev-storage.c | 36 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index f47c856..f50bcb8 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -610,6 +610,23 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
         return;
     }
 
+    bdrv_add_key(blk_bs(blk), NULL, &err);
+    if (err) {
+        if (monitor_cur_is_qmp()) {
+            error_propagate(errp, err);
+            return;
+        }
+        error_free(err);
+        err = NULL;
+        if (cur_mon) {
+            monitor_read_bdrv_key_start(cur_mon, blk_bs(blk),
+                                        usb_msd_password_cb, s);
+            s->dev.auto_attach = 0;
+        } else {
+            autostart = 0;
+        }
+    }
+
     blkconf_serial(&s->conf, &dev->serial);
     blkconf_blocksizes(&s->conf);
 
@@ -638,25 +655,6 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
     }
     usb_msd_handle_reset(dev);
     s->scsi_dev = scsi_dev;
-
-    if (bdrv_key_required(blk_bs(blk))) {
-        if (cur_mon) {
-            bdrv_add_key(blk_bs(blk), NULL, &err);
-            if (!err) {
-                usb_msd_password_cb(s, 0);
-            } else if (monitor_cur_is_qmp()) {
-                qerror_report_err(err);
-                error_free(err);
-            } else {
-                error_free(err);
-                monitor_read_bdrv_key_start(cur_mon, blk_bs(blk),
-                                            usb_msd_password_cb, s);
-            }
-            s->dev.auto_attach = 0;
-        } else {
-            autostart = 0;
-        }
-    }
 }
 
 static void usb_msd_realize_bot(USBDevice *dev, Error **errp)
-- 
1.9.3