File Access Monitoring

Tracing policies can be added to Tetragon through YAML configuration files that extend Tetragon’s base execution tracing capabilities. These policies perform filtering in kernel to ensure only interesting events are published to userspace from the BPF programs running in kernel. This ensures overhead remains low even on busy systems.

The instructions below extend the example from Execution Monitoring with a policy to monitor sensitive files in Linux. The policy used is file_monitoring.yaml, which you can review and extend as needed. Files monitored here serve as a good base set of files.

Apply the tracing policy

To apply the policy in Kubernetes, use kubectl. In Kubernetes, the policy references a Custom Resource Definition (CRD) installed by Tetragon. Docker uses the same YAML configuration file as Kubernetes, but this file is loaded from disk when the Docker container is launched.

Note that these instructions assume you’ve installed the demo application, as outlined in either the Quick Kubernetes Install or the Quick Docker Install section.

• Kubernetes (single node)
• Kubernetes (multiple nodes)
• Docker

kubectl apply -f https://raw.githubusercontent.com/cilium/tetragon/main/examples/quickstart/file_monitoring.yaml

kubectl apply -f https://raw.githubusercontent.com/cilium/tetragon/main/examples/quickstart/file_monitoring.yaml

wget https://raw.githubusercontent.com/cilium/tetragon/main/examples/quickstart/file_monitoring.yaml
docker stop tetragon
docker run -d --name tetragon --rm --pull always \
  --pid=host --cgroupns=host --privileged \
  -v ${PWD}/file_monitoring.yaml:/etc/tetragon/tetragon.tp.d/file_monitoring.yaml \
  -v /sys/kernel/btf/vmlinux:/var/lib/tetragon/btf \
  quay.io/cilium/tetragon:latest

Observe Tetragon file access events

With the tracing policy applied you can attach tetra to observe events again:

• Kubernetes (single node)
• Kubernetes (multiple nodes)
• Docker

kubectl exec -ti -n kube-system ds/tetragon -c tetragon -- tetra getevents -o compact --pods xwing

POD=$(kubectl -n kubesystem get pods -l 'app.kubernetes.io/name=tetragon' -o name --field-selector spec.nodeName=$(kubectl get pod xwing -o jsonpath='{.spec.nodeName}'))
kubectl exec -ti -n kube-system $POD -c tetragon -- tetra getevents -o compact --pods xwing

docker exec -ti tetragon tetra getevents -o compact

To generate an event, try to read a sensitive file referenced in the policy.

• Kubernetes (single node)
• Kubernetes (multiple nodes)
• Docker

kubectl exec -ti xwing -- bash -c 'cat /etc/shadow'

kubectl exec -ti xwing -- bash -c 'cat /etc/shadow'

cat /etc/shadow

This will generate a read event (Docker events will omit Kubernetes metadata shown below) that looks something like this:

🚀 process default/xwing /bin/bash -c "cat /etc/shadow"
🚀 process default/xwing /bin/cat /etc/shadow
📚 read    default/xwing /bin/cat /etc/shadow
💥 exit    default/xwing /bin/cat /etc/shadow 0

Per the tracing policy, Tetragon generates write events in responses to attempts to write in sensitive directories (for example, attempting to write in the /etc directory).

• Kubernetes (single node)
• Kubernetes (multiple nodes)
• Docker

kubectl exec -ti xwing -- bash -c 'echo foo >> /etc/bar'

kubectl exec -ti xwing -- bash -c 'echo foo >> /etc/bar'

echo foo >> /etc/bar

In response, you will see output similar to the following (Docker events do not include the Kubernetes metadata shown here).

🚀 process default/xwing /bin/bash -c "echo foo >>  /etc/bar"
📝 write   default/xwing /bin/bash /etc/bar
📝 write   default/xwing /bin/bash /etc/bar
💥 exit    default/xwing /bin/bash -c "echo foo >>  /etc/bar

What’s next

To explore tracing policies for networking see the Networking Monitoring section of the Getting Started guide. To dive into the details of policies and events please see the Concepts section of the documentation.