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Agent plugin: WorkloadAttestor "unix"

The unix plugin generates unix-based selectors for workloads calling the agent.

Configuration Description Default
discover_workload_path If true, the workload path will be discovered by the plugin and used to provide additional selectors false
workload_size_limit The limit of workload binary sizes when calculating certain selectors (e.g. sha256). If zero, no limit is enforced. 0

If configured with discover_workload_path = true, the plugin will discover the workload path to provide additional selectors. If the plugin cannot discover the workload path or gather selectors based on the path, it will fail the attestation attempt. Discovering the workload path requires the agent to have sufficient platform-specific permissions. For example, on Linux, the agent would need to be able to read /proc/<WORKLOAD PID>/exe, likely requiring the agent to either run as root or the same user as the workload. Care must be taken to only enable this option if the agent will be run with sufficient permissions.

General selectors:

Selector Value
unix:uid The user ID of the workload (e.g. unix:uid:1000)
unix:user The user name of the workload (e.g. unix:user:nginx)
unix:gid The group ID of the workload (e.g. unix:gid:1000)
unix:group The group name of the workload (e.g. unix:group:www-data)

Workload path enabled selectors (available when configured with discover_workload_path = true):

Selector Value
unix:path The path to the workload binary (e.g. unix:path:/usr/bin/nginx)
unix:sha256 The SHA256 digest of the workload binary (e.g. unix:sha256:3a6eb0790f39ac87c94f3856b2dd2c5d110e6811602261a9a923d3bb23adc8b7)

Security Considerations:

Malicious workloads could cause the SPIRE agent to do expensive work calculating a sha256 for large workload binaries, causing a denial-of-service. This plugin includes a configuration value that can be used to mitigate such an attack (i.e. workload_size_limit) by enforcing a limit on the binary size the plugin is willing to hash. The same attack could be performed by spawning a bunch of processes under the limit. The workload API does not yet support rate limiting, but when it does, this attack can be mitigated by using rate limiting in conjunction with workload_size_limit.

A sample configuration:

	WorkloadAttestor "unix" {
		plugin_data {
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