HADOOP-12687. SecureUtil#QualifiedHostResolver#getByName should also try to resolve direct hostname (Sunil G via rohithsharmaks)

(cherry picked from commit 2b252844e04eebd4f32815d4bd6f914c02994709)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -19,6 +19,10 @@ Release 2.9.0 - UNRELEASED
 
   BUG FIXES
 
+    HADOOP-12687. SecureUtil#QualifiedHostResolver#getByName should also try to
+    resolve direct hostname, incase multiple loopback addresses are present in
+    /etc/hosts (Sunil G via rohithsharmaks)
+
 Release 2.8.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/SecurityUtil.java

@@ -580,7 +580,13 @@ public class SecurityUtil {
           addr = getByNameWithSearch(host);
           if (addr == null) {
             addr = getByExactName(host);
+            // If multiple loopback addresses are present, a direct lookup
+            // will be helpful
+            if (addr == null) {
+              addr = InetAddress.getByName(host);
+            }
           }
+
         }
       }
       // unresolvable!