This bug is being split off from bugid 4690407. Part of that bug report
says:

Try the following from the command line:

jar -vcfm0 cfmi0.jar dummy.mf Dummy.class
jar -i0 cfmi0.jar

    The second "jar" call fails with the
    stack trace below:


ERROR MESSAGES/STACK TRACES THAT OCCUR :
sun.tools.jar.JarException: incorrect length while processing: .\index31601.tmp
        at sun.tools.jar.Main.crc32File(Main.java:665)
        at sun.tools.jar.Main.addIndex(Main.java:505)
        at sun.tools.jar.Main.update(Main.java:435)
        at sun.tools.jar.Main.dumpIndex(Main.java:768)
        at sun.tools.jar.Main.genIndex(Main.java:842)
        at sun.tools.jar.Main.run(Main.java:196)
        at sun.tools.jar.Main.main(Main.java:904)


This bug can be reproduced always.