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

[Alex Jia]

On 07/16/2013 04:35 PM, Peter Krempa wrote:

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 <a...@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;
        }

Yes, I will add it into v2, thanks for your review.

        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

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