Re: [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  0x7f39429507f6 in qemuAgentGetVCPUs (mon=0x0, info=0x7f394b0909b8) at 
qemu/qemu_agent.c:1475
#4  0x7f39429d9857 in qemuDomainGetVcpusFlags (dom=value optimized out, 
flags=9) at qemu/qemu_driver.c:4849
#5  0x7f3957dffd8d in virDomainGetVcpusFlags (domain=0x7f3939c0, 
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;
}
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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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  0x7f39429507f6 in qemuAgentGetVCPUs (mon=0x0, 
info=0x7f394b0909b8) at qemu/qemu_agent.c:1475
#4  0x7f39429d9857 in qemuDomainGetVcpusFlags (dom=value 
optimized out, flags=9) at qemu/qemu_driver.c:4849
#5  0x7f3957dffd8d in virDomainGetVcpusFlags 
(domain=0x7f3939c0, 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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