Help with 4.3 mod to kill uninteruptable procs.

[Dan Bernstein]

In article <10112 at dog.ee.lbl.gov> torek at elf.ee.lbl.gov (Chris Torek) writes:
> If (A) you have SIGSTOP and (B) signals work correctly,
> the super-user can stop everything, pick out the bad processes, kill
> them, and then resume everything.  (This is a bit tricky to get right,
> admittedly.)

What's tricky about it?

  #include <sys/time.h>
  #include <sys/resource.h>
  #include <signal.h>
  #include <stdio.h>
  #include <errno.h>
  extern int errno;

  main(argc,argv,envp) /* invoke as, e.g., zonk /bin/csh csh -f; untested */
  int argc;
  char *argv[];
  char *envp[];
  {
   if (getuid()) { fprintf(stderr,"zonk: fatal: uid not 0\n"); exit(1); }
   if (geteuid()) { fprintf(stderr,"zonk: fatal: euid not 0\n"); exit(2); }
   if (setpriority(PRIO_PROCESS,0,-20))
     fprintf(stderr,"zonk: weird: can't set my priority to -20\n");
   if (kill(-1,SIGSTOP) == -1) perror("zonk: warning: first kill failed");
   if (kill(-1,SIGSTOP) == -1) perror("zonk: warning: second kill failed");
   if (kill(-1,SIGSTOP) == -1) perror("zonk: warning: good-luck kill failed");
   for (;;)
    {
     (void) execve(argv[1],argv + 2,envp);
     perror("zonk: critical: exec failed, will try again");
     sleep(60);
    }
  }

---Dan