setgid on /etc/elasticearch on package install

When creating the keystore explicitly (from executing
elasticsearch-keystore create) or implicitly (for plugins that require
the keystore to be created on install) on an Elasticsearch package
installation, we are running as the root user. This leaves
/etc/elasticsearch/elasticsearch.keystore having the wrong ownership
(root:root) so that the elasticsearch user can not read the keystore on
startup. This commit adds setgid to /etc/elasticsearch on package
installation so that when executing this directory (as we would when
creating the keystore), we will end up with the correct ownership
(root:elasticsearch). Additionally, we set the permissions on the
keystore to be 660 so that the elasticsearch user via its group can read
this file on startup.

Relates #26412

core/src/main/java/org/elasticsearch/common/settings/KeyStoreWrapper.java

@@ -330,7 +330,7 @@ public void save(Path configDir) throws Exception {
         PosixFileAttributeView attrs = Files.getFileAttributeView(keystoreFile, PosixFileAttributeView.class);
         if (attrs != null) {
             // don't rely on umask: ensure the keystore has minimal permissions
-            attrs.setPermissions(PosixFilePermissions.fromString("rw-------"));
+            attrs.setPermissions(PosixFilePermissions.fromString("rw-rw----"));
         }
     }
 

distribution/src/main/packaging/scripts/postinst

@@ -100,6 +100,7 @@ fi
 chown -R elasticsearch:elasticsearch /var/lib/elasticsearch
 chown -R elasticsearch:elasticsearch /var/log/elasticsearch
 chown -R root:elasticsearch /etc/elasticsearch
+chmod g+s /etc/elasticsearch
 chmod 0750 /etc/elasticsearch
 
 if [ -f /etc/default/elasticsearch ]; then

qa/vagrant/src/test/resources/packaging/utils/packages.bash

@@ -94,7 +94,7 @@ verify_package_installation() {
     assert_file "$ESHOME/bin/elasticsearch-plugin" f root root 755
     assert_file "$ESHOME/bin/elasticsearch-translog" f root root 755
     assert_file "$ESHOME/lib" d root root 755
-    assert_file "$ESCONFIG" d root elasticsearch 750
+    assert_file "$ESCONFIG" d root elasticsearch 2750
     assert_file "$ESCONFIG/elasticsearch.yml" f root elasticsearch 660
     assert_file "$ESCONFIG/jvm.options" f root elasticsearch 660
     assert_file "$ESCONFIG/log4j2.properties" f root elasticsearch 660