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https://issues.apache.org/jira/browse/HADOOP-17488?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ahmed Hussein updated HADOOP-17488:
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Affects Version/s: 3.4.0
2.10.1
> Race condition refreshing NetgroupCache
> ----------------------------------------
>
> Key: HADOOP-17488
> URL: https://issues.apache.org/jira/browse/HADOOP-17488
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.10.1, 3.4.0
> Reporter: Ahmed Hussein
> Assignee: Ahmed Hussein
> Priority: Major
>
> There is potential concurrency bug in the {{NetgroupCache}} implementation.
> {{NetgroupCache}} is static. When ACL is built, its groups will be added to
> the {{NetgroupCache}}.
> A {{-refreshUserToGroupsMappings}} forces the cache to reload the users for
> each group.
> This is done by first getting the keys, clearing the cache, then finally
> reloading the users for each group.
> The problem that the three steps are not atomic.
> Adding ACLs concurrently may take place between L80-L81
> ([JniBasedUnixGroupsNetgroupMapping#L79|https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/JniBasedUnixGroupsNetgroupMapping.java#L79]).
> This results in the loss of the most recently added group.
> Since group names are used in the JNI level, the users of that group won't
> be retrieved.
> {code:java}
> 78 @Override
> 79 public void cacheGroupsRefresh() throws IOException {
> 80 List<String> groups = NetgroupCache.getNetgroupNames();
> 81 NetgroupCache.clear();
> 82 cacheGroupsAdd(groups);
> 83 }
> {code}
> +Solution:+
> Refreshing {{NetgroupCache}} should not clear the cache keys.
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