From 5a4c2374a2ca5d9d5c5d495f507abcef0f5aabe7 Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Nov 08 2013 06:31:02 +0000
Subject: qemu: Avoid double free of VM


One of my previous patches (c7ac2519b7f) did try to fix the issue when
domain dies too soon during migration. However, this clumsy approach was
missing removal of qemuProcessHandleMonitorDestroy resulting in double
unrefing of mon->vm and hence producing the daemon crash:

==11843== Invalid read of size 4
==11843==    at 0x50C28C5: virObjectUnref (virobject.c:255)
==11843==    by 0x1148F7DB: qemuMonitorDispose (qemu_monitor.c:258)
==11843==    by 0x50C2991: virObjectUnref (virobject.c:262)
==11843==    by 0x50C2D13: virObjectFreeCallback (virobject.c:388)
==11843==    by 0x509C37B: virEventPollCleanupHandles (vireventpoll.c:583)
==11843==    by 0x509C711: virEventPollRunOnce (vireventpoll.c:652)
==11843==    by 0x509A620: virEventRunDefaultImpl (virevent.c:274)
==11843==    by 0x520D21C: virNetServerRun (virnetserver.c:1112)
==11843==    by 0x11F368: main (libvirtd.c:1513)
==11843==  Address 0x13b88864 is 4 bytes inside a block of size 136 free'd
==11843==    at 0x4A07F5C: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==11843==    by 0x5079A2F: virFree (viralloc.c:580)
==11843==    by 0x50C29E3: virObjectUnref (virobject.c:270)
==11843==    by 0x114770E4: qemuProcessHandleMonitorDestroy (qemu_process.c:1103)
==11843==    by 0x1148F7CB: qemuMonitorDispose (qemu_monitor.c:257)
==11843==    by 0x50C2991: virObjectUnref (virobject.c:262)
==11843==    by 0x50C2D13: virObjectFreeCallback (virobject.c:388)
==11843==    by 0x509C37B: virEventPollCleanupHandles (vireventpoll.c:583)
==11843==    by 0x509C711: virEventPollRunOnce (vireventpoll.c:652)
==11843==    by 0x509A620: virEventRunDefaultImpl (virevent.c:274)
==11843==    by 0x520D21C: virNetServerRun (virnetserver.c:1112)
==11843==    by 0x11F368: main (libvirtd.c:1513)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

---

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 7c23eb4..6cb8a60 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -1095,14 +1095,6 @@ error:
     return -1;
 }
 
-
-static void qemuProcessHandleMonitorDestroy(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
-                                            virDomainObjPtr vm,
-                                            void *opaque ATTRIBUTE_UNUSED)
-{
-    virObjectUnref(vm);
-}
-
 static int
 qemuProcessHandleTrayChange(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
                             virDomainObjPtr vm,
@@ -1366,7 +1358,6 @@ cleanup:
 
 
 static qemuMonitorCallbacks monitorCallbacks = {
-    .destroy = qemuProcessHandleMonitorDestroy,
     .eofNotify = qemuProcessHandleMonitorEOF,
     .errorNotify = qemuProcessHandleMonitorError,
     .diskSecretLookup = qemuProcessFindVolumeQcowPassphrase,
@@ -1403,7 +1394,7 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int logfd)
     }
 
     /* Hold an extra reference because we can't allow 'vm' to be
-     * deleted while the monitor is active */
+     * deleted unitl the monitor gets its own reference. */
     virObjectRef(vm);
 
     ignore_value(virTimeMillisNow(&priv->monStart));
@@ -1419,11 +1410,10 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int logfd)
         ignore_value(qemuMonitorSetDomainLog(mon, logfd));
 
     virObjectLock(vm);
+    virObjectUnref(vm);
     priv->monStart = 0;
 
-    if (mon == NULL) {
-        virObjectUnref(vm);
-    } else if (!virDomainObjIsActive(vm)) {
+    if (!virDomainObjIsActive(vm)) {
         qemuMonitorClose(mon);
         mon = NULL;
     }