[jira] [Created] (MAPREDUCE-4485) container-executor should deal with file descriptors better

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

Colin Patrick McCabe created MAPREDUCE-4485:
-----------------------------------------------

             Summary: container-executor should deal with file descriptors better
                 Key: MAPREDUCE-4485
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4485
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: nodemanager
            Reporter: Colin Patrick McCabe
            Priority: Minor


container-executor.c contains the following code:

{code}
  fclose(stdin);
  fflush(LOGFILE);
  if (LOGFILE != stdout) {
    fclose(stdout);
  }
  if (ERRORFILE != stderr) {
    fclose(stderr);
  }
  if (chdir(primary_app_dir) != 0) {
    fprintf(LOGFILE, "Failed to chdir to app dir - %s\n", strerror(errno));
    return -1;
  }
  execvp(args[0], args);
{code}

Whenever you open a new file descriptor, its number is the lowest available number.  So if {{stdout}} (fd number 1) has been closed, and you do open("/my/important/file"), you'll get assigned file descriptor 1.  This means that any printf statements in the program will be now printing to /my/important/file.  Oops!

The correct way to get rid of stdin, stdout, or stderr is not to close them, but to make them point to /dev/null.  {{dup2}} can be used for this purpose.

Another thing we should be doing in container-executor.c is closing any file descriptors we don't need.  Because container-executor was forked off of the JVM, any file that was open at the time the JVM called fork() will also be open for us.  These FDs will contain to be open even after the {{execve}}, unless we close them manually.  This could be both a resource leak and a security breach.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira