[jira] [Created] (HADOOP-12676) Consider the default keytab file of Kerberos

["Tianyin Xu (JIRA)" <ji...@apache.org>]

Tianyin Xu created HADOOP-12676:
-----------------------------------

             Summary: Consider the default keytab file of Kerberos
                 Key: HADOOP-12676
                 URL: https://issues.apache.org/jira/browse/HADOOP-12676
             Project: Hadoop Common
          Issue Type: Improvement
          Components: security
    Affects Versions: 2.6.2, 2.7.1
            Reporter: Tianyin Xu
            Priority: Minor


In the current implementation of {{SecurityUtil}}, we do not consider the default keytab file of Kerberos (which is {{/etc/krb5.keytab}} in [MIT Kerberos defaults|http://web.mit.edu/kerberos/krb5-1.13/doc/mitK5defaults.html#paths]).

If the user does not set the keytab file, an {{IOException}} will be thrown. 
{code:title=SecurityUtil.java|borderStyle=solid}
230   public static void login(final Configuration conf,
231       final String keytabFileKey, final String userNameKey, String hostname)
232       throws IOException { 
...
237     String keytabFilename = conf.get(keytabFileKey);
238     if (keytabFilename == null || keytabFilename.length() == 0) {
239       throw new IOException("Running in secure mode, but config doesn't have a keytab");
240     }
{code} 

However, the default keytab location is assumed by some of the callers. For example, in [{{yarn-default.xml}}|https://hadoop.apache.org/docs/r2.7.1/hadoop-yarn/hadoop-yarn-common/yarn-default.xml], the defaults of {{yarn.resourcemanager.keytab}}, {{yarn.nodemanager.keytab}}, and {{yarn.timeline-service.keytab}} all point to {{/etc/krb5.keytab}}. 

On the other hand, these callers directly call the {{SecurityUtil.login}} method; therefore, the docs are incorrect that the defaults are actually {{null}} (as we do not have a default)...
{code:title=NodeManager.java|borderStyle=solid}
  protected void doSecureLogin() throws IOException {
    SecurityUtil.login(getConfig(), YarnConfiguration.NM_KEYTAB,
        YarnConfiguration.NM_PRINCIPAL);
  }
{code}

I don't know if we should make {{/etc/krb5.keytab}} as the default in {{SecurityUtil}}, or ask the callers to correct their assumptions. I post here as a potential improvement.

Thanks!



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