[libvirt] [PATCH 4/4] qemu: Obtain reference on monConfig

[Marc Hartmayer]

On Mon, Apr 09, 2018 at 04:25 PM +0200, Marc Hartmayer <mhartmay at linux.vnet.ibm.com> wrote:
> On Fri, Apr 06, 2018 at 06:53 PM +0200, John Ferlan <jferlan at redhat.com> wrote:
>> Because we allow a QEMU_JOB_DESTROY to occur while we're starting
>> up and we drop the @vm lock prior to qemuMonitorOpen, it's possible
>> that a domain destroy operation "wins" the race, calls qemuProcessStop
>> which will free and reinitialize priv->monConfig. Depending on the
>> exact timing either qemuMonitorOpen will be passed a NULL @config
>> variable or it will be using free'd (and possibly reclaimed) memory
>> as the @config parameter - neither of which is good.
>>
>> Resolve this by localizing the @monConfig, taking an extra reference,
>> and then once we get the @vm lock again removing our reference since
>> we are done with it.
>>
>> Signed-off-by: John Ferlan <jferlan at redhat.com>
>> ---
>>  src/qemu/qemu_process.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
>> index a8dab92dd6..988c6b1537 100644
>> --- a/src/qemu/qemu_process.c
>> +++ b/src/qemu/qemu_process.c
>> @@ -1776,6 +1776,7 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int asyncJob,
>>      qemuDomainObjPrivatePtr priv = vm->privateData;
>>      qemuMonitorPtr mon = NULL;
>>      unsigned long long timeout = 0;
>> +    virDomainChrSourceDefPtr monConfig;
>>
>>      if (qemuSecuritySetDaemonSocketLabel(driver->securityManager, vm->def) < 0) {
>>          VIR_ERROR(_("Failed to set security context for monitor for %s"),
>> @@ -1794,10 +1795,12 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int asyncJob,
>>      virObjectRef(vm);
>>
>>      ignore_value(virTimeMillisNow(&priv->monStart));
>> +    monConfig = priv->monConfig;
>> +    virObjectRef(monConfig);
>>      virObjectUnlock(vm);
>>
>>      mon = qemuMonitorOpen(vm,
>> -                          priv->monConfig,
>> +                          monConfig,
>>                            priv->monJSON,
>>                            timeout,
>>                            &monitorCallbacks,
>> @@ -1813,6 +1816,7 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int asyncJob,
>>
>>      virObjectLock(vm);
>>      virObjectUnref(vm);
>> +    virObjectUnref(monConfig);
>
> Only for consistency: I would first unref @monConfig and then do the
> unref for @vm.

With this change: Reviewed-by: Marc Hartmayer <mhartmay at linux.vnet.ibm.com>

>
>>      priv->monStart = 0;
>>
>>      if (!virDomainObjIsActive(vm)) {
>> --
>> 2.13.6
>>
>> --
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>>
> --
> Beste Grüße / Kind regards
>    Marc Hartmayer
>
> IBM Deutschland Research & Development GmbH
> Vorsitzende des Aufsichtsrats: Martina Koederitz
> Geschäftsführung: Dirk Wittkopp
> Sitz der Gesellschaft: Böblingen
> Registergericht: Amtsgericht Stuttgart, HRB 243294
--
Beste Grüße / Kind regards
   Marc Hartmayer

IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294