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From 5f78e7c3588d19b63acd717a53a62fca1971fc9a Mon Sep 17 00:00:00 2001
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Message-Id: <5f78e7c3588d19b63acd717a53a62fca1971fc9a.1383922565.git.jdenemar@redhat.com>
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From: Michal Privoznik <mprivozn@redhat.com>
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Date: Fri, 8 Nov 2013 08:01:41 +0100
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Subject: [PATCH] qemu: Avoid double free of VM
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https://bugzilla.redhat.com/show_bug.cgi?id=1018267
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One of my previous patches (c7ac2519b7f) did try to fix the issue when
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domain dies too soon during migration. However, this clumsy approach was
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missing removal of qemuProcessHandleMonitorDestroy resulting in double
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unrefing of mon->vm and hence producing the daemon crash:
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==11843== Invalid read of size 4
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==11843==    at 0x50C28C5: virObjectUnref (virobject.c:255)
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==11843==    by 0x1148F7DB: qemuMonitorDispose (qemu_monitor.c:258)
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==11843==    by 0x50C2991: virObjectUnref (virobject.c:262)
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==11843==    by 0x50C2D13: virObjectFreeCallback (virobject.c:388)
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==11843==    by 0x509C37B: virEventPollCleanupHandles (vireventpoll.c:583)
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==11843==    by 0x509C711: virEventPollRunOnce (vireventpoll.c:652)
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==11843==    by 0x509A620: virEventRunDefaultImpl (virevent.c:274)
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==11843==    by 0x520D21C: virNetServerRun (virnetserver.c:1112)
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==11843==    by 0x11F368: main (libvirtd.c:1513)
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==11843==  Address 0x13b88864 is 4 bytes inside a block of size 136 free'd
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==11843==    at 0x4A07F5C: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
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==11843==    by 0x5079A2F: virFree (viralloc.c:580)
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==11843==    by 0x50C29E3: virObjectUnref (virobject.c:270)
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==11843==    by 0x114770E4: qemuProcessHandleMonitorDestroy (qemu_process.c:1103)
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==11843==    by 0x1148F7CB: qemuMonitorDispose (qemu_monitor.c:257)
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==11843==    by 0x50C2991: virObjectUnref (virobject.c:262)
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==11843==    by 0x50C2D13: virObjectFreeCallback (virobject.c:388)
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==11843==    by 0x509C37B: virEventPollCleanupHandles (vireventpoll.c:583)
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==11843==    by 0x509C711: virEventPollRunOnce (vireventpoll.c:652)
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==11843==    by 0x509A620: virEventRunDefaultImpl (virevent.c:274)
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==11843==    by 0x520D21C: virNetServerRun (virnetserver.c:1112)
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==11843==    by 0x11F368: main (libvirtd.c:1513)
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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(cherry picked from commit 5a4c2374a2ca5d9d5c5d495f507abcef0f5aabe7)
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Conflicts:
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	src/qemu/qemu_process.c: Context, as 809ee6bad is not backported yet.
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Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
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---
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 src/qemu/qemu_process.c | 15 +++------------
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 1 file changed, 3 insertions(+), 12 deletions(-)
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diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
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index b9f291d..e0097df 100644
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--- a/src/qemu/qemu_process.c
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+++ b/src/qemu/qemu_process.c
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@@ -1082,13 +1082,6 @@ error:
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     return -1;
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 }
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-
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-static void qemuProcessHandleMonitorDestroy(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
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-                                            virDomainObjPtr vm)
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-{
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-    virObjectUnref(vm);
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-}
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-
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 static int
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 qemuProcessHandleTrayChange(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
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                             virDomainObjPtr vm,
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@@ -1345,7 +1338,6 @@ cleanup:
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 static qemuMonitorCallbacks monitorCallbacks = {
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-    .destroy = qemuProcessHandleMonitorDestroy,
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     .eofNotify = qemuProcessHandleMonitorEOF,
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     .errorNotify = qemuProcessHandleMonitorError,
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     .diskSecretLookup = qemuProcessFindVolumeQcowPassphrase,
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@@ -1382,7 +1374,7 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int logfd)
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     }
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     /* Hold an extra reference because we can't allow 'vm' to be
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-     * deleted while the monitor is active */
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+     * deleted unitl the monitor gets its own reference. */
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     virObjectRef(vm);
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     ignore_value(virTimeMillisNow(&priv->monStart));
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@@ -1397,11 +1389,10 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int logfd)
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         ignore_value(qemuMonitorSetDomainLog(mon, logfd));
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     virObjectLock(vm);
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+    virObjectUnref(vm);
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     priv->monStart = 0;
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-    if (mon == NULL) {
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-        virObjectUnref(vm);
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-    } else if (!virDomainObjIsActive(vm)) {
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+    if (!virDomainObjIsActive(vm)) {
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         qemuMonitorClose(mon);
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         mon = NULL;
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     }
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-- 
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1.8.4.2
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