Add a new stage for configuring SELinux state on the system

Add a new `org.osbuild.selinux.config` stage to configure the
SELinux state on the system.

The stage configures the SELinux state on the system in /etc/selinux/config.
The policy enforcement state and active policy type can be configured.

Fix osbuild#785

Signed-off-by: Tomas Hozza <thozza@redhat.com>

stages/org.osbuild.selinux.config

@@ -0,0 +1,65 @@
+#!/usr/bin/python3
+"""
+Configure the SELinux state on the system.
+
+The stage configures the SELinux state on the system in /etc/selinux/config.
+The policy enforcement state and active policy type can be configured.
+"""
+
+
+import sys
+
+import osbuild.api
+
+
+SCHEMA = """
+"additionalProperties": false,
+"description": "SELinux state configuration.",
+"properties": {
+  "state": {
+    "type": "string",
+    "description": "The active policy enforcement state.",
+    "enum": ["enforcing", "permissive", "disabled"]
+  },
+  "type": {
+    "type": "string",
+    "description": "The active policy type.",
+    "enum": ["targeted", "minimum", "mls"]
+  }
+}
+"""
+
+
+def main(tree, options):
+    state = options.get("state")
+    policy_type = options.get("type")
+
+    selinux_config_file = "/etc/selinux/config"
+    selinux_state_key = "SELINUX"
+    selinux_type_key = "SELINUXTYPE"
+
+    selinux_config_lines = []
+    with open(f"{tree}{selinux_config_file}") as f:
+        selinux_config_lines = f.readlines()
+
+    for idx, line in enumerate(selinux_config_lines):
+        if line.startswith("#") or not line.strip():
+            continue
+
+        line_key, _ = line.strip().split("=", 1)
+
+        if line_key == selinux_state_key:
+            selinux_config_lines[idx] = f"{selinux_state_key}={state}\n"
+        elif line_key == selinux_type_key and policy_type:
+            selinux_config_lines[idx] = f"{selinux_type_key}={policy_type}\n"
+
+    with open(f"{tree}{selinux_config_file}", "w") as f:
+        f.writelines(selinux_config_lines)
+
+    return 0
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    r = main(args["tree"], args["options"])
+    sys.exit(r)