File Access Monitoring

Tracing Policies can be added to Tetragon through YAML configuration files that extend Tetragon’s base execution tracing capabilities. These policies do 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 following extends the example from Execution Tracing with a policy to monitor sensitive files in Linux. The policy used is the file_monitoring.yaml it can be reviewed and extended as needed. Files monitored here serve as a good base set of files.

To apply the policy Kubernetes uses a CRD that can be applied with kubectl. Uses the same YAML configuration as Kuberenetes, but loaded through a file on disk.

• Kubernetes
• Docker

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-container
docker run --name tetragon-container --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-ci:latest

With the file applied we can attach tetra to observe events again:

• Kubernetes
• Docker

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

docker exec tetragon-container tetra getevents -o compact

Then reading a sensitive file:

• Kubernetes
• Docker

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

cat /etc/shadow

This will generate a read event (Docker events will omit Kubernetes metadata),

🚀 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

Attempts to write in sensitive directories will similarly create write events. For example, attempting to write in /etc.

• Kubernetes
• Docker

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

cat /etc/shadow

Will result in the following output in the tetra CLI.

🚀 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 try the Networking Monitoring quickstart. To dive into the details of policies and events please see Concepts section.