[libvirt] [PATCH 3/3] qemu: agent: take monitor lock in qemuAgentNotifyEvent

[John Ferlan]

On 11/24/2016 04:19 AM, Nikolay Shirokovskiy wrote:
> qemuAgentNotifyEvent notify on a lock condition without taking
> the lock. This works but it is a subject to race conditions.
> ---
>  src/qemu/qemu_agent.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 

But the vm is locked prior to any priv->agent dereference and call - so
what path could free priv->agent before we get into this NotifyEvent
code?  I suppose it wouldn't hurt, but we're not entering the agent and
the AgentEOF would require vm lock to clear agent.

John

> diff --git a/src/qemu/qemu_agent.c b/src/qemu/qemu_agent.c
> index 5230cbc..ad031d0 100644
> --- a/src/qemu/qemu_agent.c
> +++ b/src/qemu/qemu_agent.c
> @@ -1248,6 +1248,8 @@ qemuAgentMakeStringsArray(const char **strings, unsigned int len)
>  void qemuAgentNotifyEvent(qemuAgentPtr mon,
>                            qemuAgentEvent event)
>  {
> +    virObjectLock(mon);
> +
>      VIR_DEBUG("mon=%p event=%d await_event=%d", mon, event, mon->await_event);
>      if (mon->await_event == event) {
>          mon->await_event = QEMU_AGENT_EVENT_NONE;
> @@ -1257,6 +1259,8 @@ void qemuAgentNotifyEvent(qemuAgentPtr mon,
>              virCondSignal(&mon->notify);
>          }
>      }
> +
> +    virObjectUnlock(mon);
>  }
>  
>  VIR_ENUM_DECL(qemuAgentShutdownMode);
>