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https://issues.apache.org/jira/browse/HDFS-14305?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16938950#comment-16938950
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Arpit Agarwal commented on HDFS-14305:
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I agree and I had the same question back in Feb. I was convinced by Erik's
response.
> Serial number in BlockTokenSecretManager could overlap between different
> namenodes
> ----------------------------------------------------------------------------------
>
> Key: HDFS-14305
> URL: https://issues.apache.org/jira/browse/HDFS-14305
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode, security
> Reporter: Chao Sun
> Assignee: Xiaoqiao He
> Priority: Major
> Fix For: 3.0.4, 3.3.0, 3.2.1, 3.1.3
>
> Attachments: HDFS-14305.001.patch, HDFS-14305.002.patch,
> HDFS-14305.003.patch, HDFS-14305.004.patch, HDFS-14305.005.patch,
> HDFS-14305.006.patch
>
>
> Currently, a {{BlockTokenSecretManager}} starts with a random integer as the
> initial serial number, and then use this formula to rotate it:
> {code:java}
> this.intRange = Integer.MAX_VALUE / numNNs;
> this.nnRangeStart = intRange * nnIndex;
> this.serialNo = (this.serialNo % intRange) + (nnRangeStart);
> {code}
> while {{numNNs}} is the total number of NameNodes in the cluster, and
> {{nnIndex}} is the index of the current NameNode specified in the
> configuration {{dfs.ha.namenodes.<nameservice>}}.
> However, with this approach, different NameNode could have overlapping ranges
> for serial number. For simplicity, let's assume {{Integer.MAX_VALUE}} is 100,
> and we have 2 NameNodes {{nn1}} and {{nn2}} in configuration. Then the ranges
> for these two are:
> {code}
> nn1 -> [-49, 49]
> nn2 -> [1, 99]
> {code}
> This is because the initial serial number could be any negative integer.
> Moreover, when the keys are updated, the serial number will again be updated
> with the formula:
> {code}
> this.serialNo = (this.serialNo % intRange) + (nnRangeStart);
> {code}
> which means the new serial number could be updated to a range that belongs to
> a different NameNode, thus increasing the chance of collision again.
> When the collision happens, DataNodes could overwrite an existing key which
> will cause clients to fail because of {{InvalidToken}} error.
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