src/process.c

   1 /* process.c -- child process routines for vlock,
   2  *              the VT locking program for linux
   3  *
   4  * This program is copyright (C) 2007 Frank Benkstein, and is free
   5  * software which is freely distributable under the terms of the
   6  * GNU General Public License version 2, included as the file COPYING in this
   7  * distribution.  It is NOT public domain software, and any
   8  * redistribution not permitted by the GNU General Public License is
   9  * expressly forbidden without prior written permission from
  10  * the author.
  11  *
  12  */
  13
  14 #include <stdio.h>
  15 #include <unistd.h>
  16 #include <signal.h>
  17 #include <sys/wait.h>
  18 #include <sys/resource.h>
  19 #include <sys/time.h>
  20
  21 #include "process.h"
  22
  23 /* Do nothing. */
  24 static void ignore_sigalarm(int __attribute__((unused)) signum)
  25 {
  26 }
  27
  28 bool wait_for_death(pid_t pid, long sec, long usec)
  29 {
  30   int status;
  31   struct sigaction act;
  32   struct sigaction oldact;
  33   struct itimerval timer;
  34   struct itimerval otimer;
  35   bool result;
  36
  37   /* Ignore SIGALRM.  The handler must be a real function instead of SIG_IGN
  38    * otherwise waitpid() would not get interrupted.
  39    *
  40    * There is a small window here where a previously set alarm might be
  41    * ignored.  */
  42   sigemptyset(&act.sa_mask);
  43   act.sa_handler = ignore_sigalarm;
  44   act.sa_flags = 0;
  45   sigaction(SIGALRM, &act, &oldact);
  46
  47   /* Initialize the timer. */
  48   timer.it_value.tv_sec = sec;
  49   timer.it_value.tv_usec = usec;
  50   /* No repetition. */
  51   timer.it_interval.tv_sec = 0;
  52   timer.it_interval.tv_usec = 0;
  53
  54   /* Set the timer. */
  55   setitimer(ITIMER_REAL, &timer, &otimer);
  56
  57   /* Wait until the child exits or the timer fires. */
  58   result = (waitpid(pid, &status, 0) == pid);
  59
  60   /* Possible race condition.  If an alarm was set before it may get ignored.
  61    * This is probably better than getting killed by our own alarm. */
  62
  63   /* Restore the timer. */
  64   setitimer(ITIMER_REAL, &otimer, NULL);
  65
  66   /* Restore signal handler for SIGALRM. */
  67   sigaction(SIGALRM, &oldact, NULL);
  68
  69   return result;
  70 }
  71
  72 /* Try hard to kill the given child process. */
  73 void ensure_death(pid_t pid)
  74 {
  75   int status;
  76
  77   switch (waitpid(pid, &status, WNOHANG)) {
  78     case -1:
  79       /* Not your child? */
  80       return;
  81     case 0:
  82       /* Not dead yet.  Continue. */
  83       break;
  84     default:
  85       /* Already dead.  Nothing to do. */
  86       return;
  87   }
  88
  89   /* Send SIGTERM. */
  90   (void) kill(pid, SIGTERM);
  91
  92   /* SIGTERM handler (if any) has 500ms to finish. */
  93   if (wait_for_death(pid, 0, 500000L))
  94     return;
  95
  96   // Send SIGKILL. */
  97   (void) kill(pid, SIGKILL);
  98   /* Child may be stopped.  Send SIGCONT just to be sure. */
  99   (void) kill(pid, SIGCONT);
 100
 101   /* Wait until dead.  Shouldn't take long. */
 102   (void) waitpid(pid, &status, 0);
 103 }
 104
 105 /* Close all possibly open file descriptors except STDIN_FILENO, STDOUT_FILENO
 106  * and STDERR_FILENO. */
 107 void close_all_fds(void)
 108 {
 109   struct rlimit r;
 110   int maxfd;
 111
 112   /* Get the maximum number of file descriptors. */
 113   if (getrlimit(RLIMIT_NOFILE, &r) == 0)
 114     maxfd = r.rlim_cur;
 115   else
 116     /* Hopefully safe default. */
 117     maxfd = 1024;
 118
 119   /* Close all possibly open file descriptors except STDIN_FILENO,
 120    * STDOUT_FILENO and STDERR_FILENO. */
 121   for (int i = 0; i < maxfd; i++) {
 122     switch (i) {
 123       case STDIN_FILENO:
 124       case STDOUT_FILENO:
 125       case STDERR_FILENO:
 126         break;
 127       default:
 128         (void) close(i);
 129         break;
 130     }
 131   }
 132 }