[libvirt] [PATCH] util: fix crash in virClassIsDerivedFrom for CloseCallbacks objects

[Maxim Nestratov]

06-Sep-16 17:42, Michal Privoznik пишет:

> On 05.09.2016 18:42, Maxim Nestratov wrote:
>> There is a possibility that qemu driver frees by unreferencing its
>> closeCallbacks pointer as it has the only reference to the object,
>> while in fact not all users of CloseCallbacks called thier
>> virCloseCallbacksUnset.
>>
>> Backtrace is the following:
>> Thread #1:
>> 0  in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
>> 1  in virCondWait (c=<optimized out>, m=<optimized out>)
>>      at util/virthread.c:154
>> 2  in virThreadPoolFree (pool=0x7f0810110b50)
>>      at util/virthreadpool.c:266
>> 3  in qemuStateCleanup () at qemu/qemu_driver.c:1116
>> 4  in virStateCleanup () at libvirt.c:808
>> 5  in main (argc=<optimized out>, argv=<optimized out>)
>>      at libvirtd.c:1660
>>
>> Thread #2:
>> 0  in virClassIsDerivedFrom (klass=0xdeadbeef, parent=0x7f0837c694d0) at util/virobject.c:169
>> 1  in virObjectIsClass (anyobj=anyobj at entry=0x7f08101d4760, klass=<optimized out>) at util/virobject.c:365
>> 2  in virObjectLock (anyobj=0x7f08101d4760) at util/virobject.c:317
>> 3  in virCloseCallbacksUnset (closeCallbacks=0x7f08101d4760, vm=vm at entry=0x7f08101d47b0, cb=cb at entry=0x7f081d078fc0 <qemuProcessAutoDestroy>) at util/virclosecallbacks.c:163
>> 4  in qemuProcessAutoDestroyRemove (driver=driver at entry=0x7f081018be50, vm=vm at entry=0x7f08101d47b0) at qemu/qemu_process.c:6368
>> 5  in qemuProcessStop (driver=driver at entry=0x7f081018be50, vm=vm at entry=0x7f08101d47b0, reason=reason at entry=VIR_DOMAIN_SHUTOFF_SHUTDOWN, asyncJob=asyncJob at entry=QEMU_ASYNC_JOB_NONE, flags=flags at entry=0) at qemu/qemu_process.c:5854
>> 6  in processMonitorEOFEvent (vm=0x7f08101d47b0, driver=0x7f081018be50) at qemu/qemu_driver.c:4585
>> 7  qemuProcessEventHandler (data=<optimized out>, opaque=0x7f081018be50) at qemu/qemu_driver.c:4629
>> 8  in virThreadPoolWorker (opaque=opaque at entry=0x7f0837c4f820) at util/virthreadpool.c:145
>> 9  in virThreadHelper (data=<optimized out>) at util/virthread.c:206
>> 10 in start_thread () from /lib64/libpthread.so.0
>>
>> Let's reference CloseCallbacks object in virCloseCallbacksSet and
>> unreference in virCloseCallbacksUnset.
>>
>> Signed-off-by: Maxim Nestratov <mnestratov at virtuozzo.com>
>> ---
>>   src/util/virclosecallbacks.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/src/util/virclosecallbacks.c b/src/util/virclosecallbacks.c
>> index 82d4071..891a92b 100644
>> --- a/src/util/virclosecallbacks.c
>> +++ b/src/util/virclosecallbacks.c
>> @@ -141,6 +141,7 @@ virCloseCallbacksSet(virCloseCallbacksPtr closeCallbacks,
>>           virObjectRef(vm);
>>       }
>>   
>> +    virObjectRef(closeCallbacks);
>>       ret = 0;
>>    cleanup:
>>       virObjectUnlock(closeCallbacks);
>> @@ -180,6 +181,8 @@ virCloseCallbacksUnset(virCloseCallbacksPtr closeCallbacks,
>>       ret = 0;
>>    cleanup:
>>       virObjectUnlock(closeCallbacks);
>> +    if (!ret)
>> +        virObjectUnref(closeCallbacks);
> Might as well put this a few lines above, just before 'ret = 0' line.
>
> ACK with that changed.
>
> Michal

No, we can't do this, as it could be the last reference to closeCallbacks and after derefencing it, virObjectUnlock 
would touch freed memory.

Maxim