POSIX-portable (i.e. glibc) way to list all open file descriptors?

ta0kira · 07-21-2007, 11:52 AM

I would like to obtain a list of all open file descriptors for a program. This is to mitigate a security issue with an exec program having access to all of its parent's file descriptors; they need to be closed before the exec call except for 0-4.

My first thought is to list all character devices in /proc/self/fd and close all but those I need. Is there a libc way to do this so that I can use this application on BSD, etc.? Thanks.
ta0kira

edit: close-on-exec should work I think...

wjevans_7d1@yahoo.co · 07-22-2007, 08:28 AM

This takes a very short time to run.

Code:

#define _POSIX_SOURCE 1

#include <stdio.h>
#include <limits.h>
#include <unistd.h>

int main(void)
{
  long open_index;
  long open_max;

#if defined(OPEN_MAX)
  open_max=OPEN_MAX;
#else
  open_max=sysconf(_SC_OPEN_MAX);
#endif

  for(open_index=5;
      open_index<open_max;
      open_index++
     )
  {
    close(open_index);
  }

  return 0;

} /* main() */

Hope this helps.

ta0kira · 07-22-2007, 01:09 PM

Yes, that indeed works. I was skeptical at first that I might be able to dup2 past OPEN_MAX, but it doesn't let me. I suppose I could create an actual list using fstat using the same method. Thanks!
ta0kira