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From hanm <...@git.apache.org>
Subject [GitHub] zookeeper pull request #179: ZOOKEEPER-2693: DOS attack on wchp/wchc four le...
Date Tue, 21 Feb 2017 17:56:53 GMT
Github user hanm commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/179#discussion_r102273810
  
    --- Diff: src/java/main/org/apache/zookeeper/server/NettyServerCnxn.java ---
    @@ -267,10 +267,17 @@ private boolean checkFourLetterWord(final Channel channel,
         {
             // We take advantage of the limited size of the length to look
             // for cmds. They are all 4-bytes which fits inside of an int
    -        String cmd = FourLetterCommands.getCmdMapView().get(len);
    -        if (cmd == null) {
    +        if (!FourLetterCommands.isKnown(len)) {
                 return false;
             }
    +
    +        // ZOOKEEPER-2693: don't execute 4lw if it's not enabled.
    +        String cmd = FourLetterCommands.getCommandString(len);
    +        if (!FourLetterCommands.isEnabled(cmd)) {
    +            LOG.debug("Command {} is not executed because it is not white listed.", cmd);
    +            return true;
    --- End diff --
    
    Thanks @arshadmohammad for your suggestion, I like this approach from a user experience
point of view as it provides nice error message on client side.
    
    I am a little bit concerned that instead of doing a (nearly) NOP on server side to block
a command the way the patch is doing now (which just cost a look up), any command including
garbage now costs some string printing plus has to go through network stack to send the bytes
back. This may lead potential vulnerable point, though it might also be OK as one could argue
if we are in such case (ZK server is wide open, every bets is off.). I tend to lean towards
the safer side though so I'll wait for a while for other comments regarding this issue.


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