If users haven't configured guest agent then qemuAgentCommand() will dereference a NULL 'mon' pointer, which causes crash of libvirtd. 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(a)redhat.com&gt; --- 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; + } + qemuDomainObjEnterAgent(vm); ncpuinfo = qemuAgentGetVCPUs(priv->agent, &cpuinfo); qemuDomainObjExitAgent(vm); @@ -4839,6 +4845,12 @@ qemuDomainGetVcpusFlags(virDomainPtr dom, unsigned int flags) if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) < 0) goto cleanup; + if (!priv->agent) { + virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s", + _("QEMU guest agent is not configured")); + goto cleanup; + } + if (!virDomainObjIsActive(vm)) { virReportError(VIR_ERR_OPERATION_INVALID, "%s", _("domain is not running")); -- 1.7.1