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Nova Networking does not enforce security group rules following a soft
reboot of an instance
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### Summary ###
In deployments using Nova Networking, security group rules associated
with an instance may not be enforced after a soft reboot. Nova is
designed to apply the configured security group rules to an instance
when certain operations are performed, such as a normal boot operation.
If an operation has been performed that results in the clearing of
security group rules, such as restarting the nova compute service, then
performing a soft reboot of that instance will cause it to be
started without security group rules being applied.

Deployments using Neutron are not impacted.

### Affected Services / Software ###
Nova, Havana, Grizzly

### Discussion ###
In Nova deployments using Nova Networking, security groups are
implemented using iptables, which is used to configure and control
network traffic into Nova instances. When an instance is first booted
using the normal boot method (nova boot <instance_id>), the security
group rules are applied to that instance.

When an instance is rebooted using the soft reboot method (nova reboot
<instance_id>), the security group rules are not reapplied since they
should have been already applied when the instance was initially
booted. If the security group rules have not been applied following an
event that resulted in their clearing, such as restarting the compute
service, the instance will be brought up without security group
enforcement. This situation is most likely to arise in cases where the
Nova compute service has been terminated or restarted, which removes
all iptables rules. If a stopped instance is then started by using a
soft reboot, it will not have any security group rules applied. A hard
reboot (nova reboot --hard <instance_id>) reapplies the security group
rules, so it is not susceptible to this issue.

Depending on the deployment architecture, this could breach security
assumptions and leave an instance vulnerable to network based attacks.

This issue only affects the Havana and Grizzly releases. The Icehouse
release does not allow a stopped instance to be started using a soft
reboot, therefore this issue does not affect the Icehouse release.

### Recommended Actions ###
Do not to use the soft reboot method to start instances from the
stopped state. If instances are in the stopped state, boot using "nova
boot <instance_id>" or reboot using "nova reboot --hard <instance_id>"
to force the security group rules to be applied.

### Contacts / References ###
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0022
Original LaunchPad Bug : https://bugs.launchpad.net/nova/+bug/1316822
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg
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