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

John Ferlan posted 4 patches 7 years, 10 months ago
[libvirt] [PATCH 4/4] qemu: Obtain reference on monConfig
Posted by John Ferlan 7 years, 10 months ago 
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@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);
     priv->monStart = 0;
 
     if (!virDomainObjIsActive(vm)) {
-- 
2.13.6

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Re: [libvirt] [PATCH 4/4] qemu: Obtain reference on monConfig
Posted by Marc Hartmayer 7 years, 10 months ago 
On Fri, Apr 06, 2018 at 06:53 PM +0200, John Ferlan <jferlan@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@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.

>      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


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Re: [libvirt] [PATCH 4/4] qemu: Obtain reference on monConfig
Posted by Marc Hartmayer 7 years, 10 months ago 
On Mon, Apr 09, 2018 at 04:25 PM +0200, Marc Hartmayer <mhartmay@linux.vnet.ibm.com> wrote:
> On Fri, Apr 06, 2018 at 06:53 PM +0200, John Ferlan <jferlan@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@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@linux.vnet.ibm.com>

>
>>      priv->monStart = 0;
>>
>>      if (!virDomainObjIsActive(vm)) {
>> --
>> 2.13.6
>>
>> --
>> libvir-list mailing list
>> libvir-list@redhat.com
>> https://www.redhat.com/mailman/listinfo/libvir-list
>>
> --
> 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


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