Re: [Valgrind-users] FD leakage

[John R. <jr...@Bi...>]

> It would be nice if valgrind reported any fd > 2 when: system(),
> popen(), or exec() was called. This is almost always a security
> problem. 

gdb 5.3 uses two fds when creating a process.  The program below outputs
  3 4 5 6 7 8 9 10 11 12
when run from a usual login shell, but it prints
  5 6 7 8 9 10 11 12 13 14
when run from gdb.  So "almost always a security problem"
might not apply in this case, and the documentation/FAQ
probably should mention it.  Also, there is a coding paradigm which
uses fd 3 as "cmdin" ["command in", for interactive/supervisory
input when stdin already has a data-stream input].
cmdin is to stdin as stderr is to stdout, sort of.

===== fd_next.c
#include <unistd.h>
#include <stdio.h>

main()
{
         int j;
         int fd[10];
         pipe(&fd[0]);
         pipe(&fd[2]);
         pipe(&fd[4]);
         pipe(&fd[6]);
         pipe(&fd[8]);
         for (j=0; j<10; ++j) {
                 printf(" %d", fd[j]);
         }
         printf("\n");
         return 0;
}
=====