64 lines
2.8 KiB
Plaintext
64 lines
2.8 KiB
Plaintext
Nova Network configuration allows guest VMs to connect to host services
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---
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### Summary ###
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When using Nova Network to manage networking for compute instances,
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instances are able to reach network services running on the host
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system. This may be a security issue for the operator.
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### Affected Services / Software ###
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Nova, Folsom, Grizzly, Havana, Icehouse
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### Discussion ###
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OpenStack deployments using Nova Network, rather than Neutron for
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network configuration will cause the host running the instances to be
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reachable on the virtual network. Specifically, booted instances can
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check the address of their gateway and try to connect to it. Any host
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service which listens on the interfaces created by OpenStack and does
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not apply any additional filtering will receive such traffic.
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This is a security issue for deployments where the OpenStack service
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users are not trusted parties, or should not be allowed to access
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underlying services of the host system.
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Using a specific example of devstack in default configuration, the
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instance spawned inside of it will see the following routing table:
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$ ip r s
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default via 172.16.1.1 dev eth0
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172.16.1.0/24 dev eth0 src 172.16.1.2
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The instance can then use the gateway's address (172.16.1.1) to connect
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to the sshd service on the host system (if one is running and listening
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on all interfaces). The host system will see the connection coming from
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interface `br100`.
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### Recommended Actions ###
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Connections like this can be stopped at various levels (libvirt filters,
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specific host's iptables entries, ebtables, network service
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configuration). The recommended way to protect against the incoming
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connections is to stop the critical services from binding to the
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Nova-controlled interfaces.
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Using the sshd service as an example, the default configuration on most
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systems is to bind to all interfaces and all local addresses
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("ListenAddress :22" in sshd_config). In order to configure it only on
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a specific interface, use "ListenAddress a.b.c.d:22" where a.b.c.d is
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the address assigned to the chosen interface. Similar settings can be
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found for most other services.
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The list of services listening on all interfaces can be obtained by
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running command 'netstat -ltu', where the '*:port' in the "Local
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Address" field means the service will likely accept connections from the
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local Nova instances.
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If filtering of the traffic is chosen instead, care must be taken to
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allow traffic coming from the running instances to services controlled
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by Nova - DHCP and DNS providers.
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### Contacts / References ###
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This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0018
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Original LaunchPad Bug : https://bugs.launchpad.net/nova/+bug/1316271
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OpenStack Security ML : openstack-security@lists.openstack.org
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OpenStack Security Group : https://launchpad.net/~openstack-ossg
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