Ahmed Hussein created HADOOP-17467:
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Summary: netgroup-user mapping breaks by a race in NetgroupCache
Key: HADOOP-17467
URL: https://issues.apache.org/jira/browse/HADOOP-17467
Project: Hadoop Common
Issue Type: Bug
Components: security
Reporter: Ahmed Hussein
Assignee: Ahmed Hussein
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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