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If users haven't configured guest agent then qemuAgentCommand() will dereference a NULL 'mon' pointer, which causes crash of libvirtd when using agent based cpu (un)plug. With the patch, when the qemu-ga service isn't running in the guest, a expected error "error: Guest agent is not responding: Guest agent not available for now" will be raised, and the error "error: argument unsupported: QEMU guest agent is not configured" is raised when the guest hasn't configured guest agent. 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@redhat.com> Signed-off-by: Peter Krempa <pkrempa@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>