Re: Cannot disable kernel's audit system via auditctl

On Thursday, June 29, 2023 6:34:03 PM EDT Samuel Bahr wrote: > Hi linux-audit, > > I'm running a fleet of Linux hosts with Red Canary Linux EDR (Endpoint > Detection and Response) which uses eBPF for gathering telemetry in service > ` cfsvcd.service`. In an older configuration, it gathered data from the > kernel's audit system and everything was fine. However, when we switched > cfsvcd to gathering data from eBPF instead, we noticed that the kernel > ring buffer was flooded with audit messages. This is because > cfsvcd.service now stops auditd.service, but leaves the kernel audit > system enabled. > > I've mitigated this issue by manually running `# auditctl -e 0` on our > hosts (via Puppet). However, I'm running into a strange issue where _some_ > hosts (~0.5%) are still logging all audit events to the kernel ring buffer > even after I have disabled the audit system via `# auditctl -e 0`. A `# > auditctl -s` run shows `enabled 0`, yet audit logs continue to flood the > kernel ring buffer. > > I'm running Linux kernel 5.4.0-1063-aws on Ubuntu 18.04 with auditctl > v2.8.2. `systemd-journald-audit.socket` is masked & inactive, ` > auditd.service` is disabled & inactive. > > I cannot entirely disable the audit system via a kernel parameter because > Red Canary Linux EDR fails to start cfsvcd.service as it fails to run some > auditctl command due to no audit support in the kernel: > > Jun 28 20:41:04 systemd[1]: Started Canary Forwarder Service. > > > Jun 28 20:41:04 cfsvcd[105781]: Found config file at path > > '"/opt/redcanary/config.json"', continuing execution... > > Jun 28 20:41:12 cfsvcd[105781]: component: Sentry > > Jun 28 20:41:12 cfsvcd[105781]: Jun 28 20:41:12.055 INFO Initializing > > Sentry Config { version: "1.4.17.release.[...]", https_proxy: None, > > extra_tags: [("telemetry.source", "eBPF")], logging_enabled: true, > > metrics_enabled: true, [...]} > > Jun 28 20:41:12 cfsvcd[105781]: Failed to setup or configure host system: > > Linux Audit watcher failure: Netlink Error: IO Error: Protocol not > > supported (os error 93) > > Jun 28 20:41:12 cfsvcd[105781]: Received stop. Exiting > > unix::wait_for_signal. Signal: 0, done.is_signaled(): true > > Jun 28 20:41:12 cfsvcd[105781]: Joining async_agent_thread > > Jun 28 20:41:13 cfsvcd[105781]: Attempting to stop subscriber (Ebpf). > > Jun 28 20:41:13 cfsvcd[105781]: Shutting down due to termination signal > > [...] > > Jun 28 20:41:15 cfsvcd[105781]: Subscriber stopped. > > Jun 28 20:41:15 auditctl[106733]: Error - audit support not in kernel > > Jun 28 20:41:15 auditctl[106733]: Cannot open netlink audit socket > > Jun 28 20:41:15 systemd[1]: cfsvcd.service: Service hold-off time over, > > scheduling restart. > > Jun 28 20:41:15 systemd[1]: cfsvcd.service: Scheduled restart job, > > restart > > counter is at 301. > > Jun 28 20:41:15 systemd[1]: Stopped Canary Forwarder Service. > > Here's the unit file for cfsvcd.service: > > [Unit] > > Description=Canary Forwarder Service > > > > DefaultDependencies=no > > After=local-fs.target systemd-tmpfiles-setup.service auditd.service > > Before=sysinit.target shutdown.target > > # Replace the auditd service if it is running > > Conflicts=auditd.service shutdown.target > > > > [Service] > > WorkingDirectory=/opt/redcanary > > ExecStart=/opt/redcanary/cfsvcd > > ExecStopPost=-/sbin/auditctl -D > > Restart=always > > TimeoutSec=15 > > > > [Install] > > WantedBy=multi-user.target > > Is this a known issue? Not really. But this is a new capability. If you run auditctl -D, does it go away? Have any of the systems been setup with auditctl -e 2? This makes the configuration immutable. -Steve > Is there a workaround to stop the logging to the > kernel ring buffer? Is there any more information I can provide to help > debug?