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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2856) Fix block protocol so that Datanodes don't require root or jsvc
Date Fri, 28 Jun 2013 18:22:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13695627#comment-13695627

Chris Nauroth commented on HDFS-2856:

Thanks for the comments, everyone.  Let's discuss the SASL point first, because it could shift
the design and make the specific questions about the proposed protocol change irrelevant.

Did you consider at all scrapping our custom authentication protocol and instead switching
to using straight SASL MD5-DIGEST for the DataTransferProtocol?

Thanks for pointing out HDFS-3637.  After further review of that patch, I see how we can iterate
on that.  I think it also has some benefits over the proposal that I posted: 1) consistency
with authentication in the rest of the codebase, and 2) enabling encryption would defeat a
man-in-the-middle attack without causing harm to intermediate proxy deployments like source
address validation might cause.  I'd like to explore the SASL solution further.

The only potential downside I see is that if we ever pipeline multiple operations over a single
connection, then we'd need to renegotiate SASL per operation, because the authorization decision
may be different per block.  This doesn't seem like an insurmountable problem though.

I have a question about the compatibility impact of HDFS-3637.  I see that an upgraded client
can talk to an old cluster, and an old client can talk to an upgraded cluster if encryption
is off.  It looks like if it's an upgraded cluster and encryption is on, then {{DataXceiver}}
will not run operations sent from unencrypted client connections, including connections initiated
from an old client.  This implies that all clients must be upgraded before it's safe to turn
on encryption in the cluster.  Do I understand correctly?  If so, can we relax this logic
a bit to allow for compatibility of an old client connected to an upgraded cluster with SASL
on?  The design doc proposed checking whether or not the datanode port is < 1024, and if
so, then allow the old connection.  The thinking here is that anyone continuing to run on
a port < 1024 must still have a component that hasn't upgraded, so therefore it needs to
support the old connection.  Once datanode has been reconfigured to run on a port >= 1024,
then all non-encrypted connections can be rejected.

Also, I wasn't sure about how the HDFS-3637 patch impacts compatibility for inter-datanode
connections.  Is it possible to have a mix of old and upgraded datanodes running, some with
encryption on and some with encryption off, or does it require a coordinated push to turn
on encryption across the whole cluster?

We wanted to be conscious of backwards compatibility with this change, particularly for a
rolling upgrade scenario.
> Fix block protocol so that Datanodes don't require root or jsvc
> ---------------------------------------------------------------
>                 Key: HDFS-2856
>                 URL: https://issues.apache.org/jira/browse/HDFS-2856
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode, security
>            Reporter: Owen O'Malley
>            Assignee: Chris Nauroth
>         Attachments: Datanode-Security-Design.pdf, Datanode-Security-Design.pdf, Datanode-Security-Design.pdf
> Since we send the block tokens unencrypted to the datanode, we currently start the datanode
as root using jsvc and get a secure (< 1024) port.
> If we have the datanode generate a nonce and send it on the connection and the sends
an hmac of the nonce back instead of the block token it won't reveal any secrets. Thus, we
wouldn't require a secure port and would not require root or jsvc.

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