[libvirt] [PATCH] qemu: Prevent crash of libvirtd without guest agent configuration

[Peter Krempa]

On 07/16/13 08:31, Alex Jia wrote:
> If users haven't configured guest agent then qemuAgentCommand() will
> dereference a NULL 'mon' pointer, which causes crash of libvirtd.

uhh, right :/ I broke that :/

>
> GDB backtrace:
>
> (gdb) bt
> #0  virNetServerFatalSignal (sig=11, siginfo=<value optimized out>, context=<value optimized out>) at rpc/virnetserver.c:326
> #1  <signal handler called>
> #2  qemuAgentCommand (mon=0x0, cmd=0x7f39300017b0, reply=0x7f394b090910, seconds=-2) at qemu/qemu_agent.c:975
> #3  0x00007f39429507f6 in qemuAgentGetVCPUs (mon=0x0, info=0x7f394b0909b8) at qemu/qemu_agent.c:1475
> #4  0x00007f39429d9857 in qemuDomainGetVcpusFlags (dom=<value optimized out>, flags=9) at qemu/qemu_driver.c:4849
> #5  0x00007f3957dffd8d in virDomainGetVcpusFlags (domain=0x7f39300009c0, flags=8) at libvirt.c:9843
>
> How to reproduce?
>
> # To start a guest without guest agent configuration
> # then run the following cmdline
>
> # virsh vcpucount foobar --guest
> error: End of file while reading data: Input/output error
> error: One or more references were leaked after disconnect from the hypervisor
> error: Failed to reconnect to the hypervisor
>
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=984821
>
> Signed-off-by: Alex Jia <ajia at redhat.com>
> ---
>   src/qemu/qemu_driver.c |   12 ++++++++++++
>   1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 495867a..1448aa7 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -4122,6 +4122,12 @@ qemuDomainSetVcpusFlags(virDomainPtr dom, unsigned int nvcpus,
>               goto endjob;
>           }
>
> +        if (!priv->agent) {
> +            virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
> +                           _("QEMU guest agent is not configured"));
> +            goto cleanup;
> +        }
> +

We probably also want:

         if (priv->agentError) {
             virReportError(VIR_ERR_AGENT_UNRESPONSIVE, "%s",
                            _("QEMU guest agent is not "
                              "available due to an error"));
             goto cleanup;
         }
         if (!priv->agent) {
             virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
                            _("QEMU guest agent is not configured"));
             goto cleanup;
         }




>           qemuDomainObjEnterAgent(vm);
>           ncpuinfo = qemuAgentGetVCPUs(priv->agent, &cpuinfo);
>           qemuDomainObjExitAgent(vm);

Peter