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

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

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4485?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Colin Patrick McCabe updated MAPREDUCE-4485:
--------------------------------------------

    Description: 
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 continue to be open even after the {{execve}}, unless we close them manually.  This could be both a resource leak and a security breach.

  was:
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.

    
> 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 continue to be open even after the {{execve}}, unless we close them manually.  This could be both a resource leak and a security breach.

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