src/vlock-all.c

   1 /* vlock-all.c -- console grabbing routine 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 <stdlib.h>
  16 #include <unistd.h>
  17 #include <fcntl.h>
  18 #include <sys/ioctl.h>
  19 #include <sys/wait.h>
  20 #include <errno.h>
  21 #include <signal.h>
  22
  23 #ifdef __FreeBSD__
  24 #include <sys/consio.h>
  25 #else
  26 #include <sys/vt.h>
  27 #endif /* __FreeBSD__ */
  28
  29 #include "vlock.h"
  30
  31 /* This handler is called by a signal whenever a user tries to
  32  * switch away from this virtual console. */
  33 void release_vt(int __attribute__((__unused__)) signum) {
  34   /* kernel is not allowed to switch */
  35   ioctl(STDIN_FILENO, VT_RELDISP, 0);
  36 }
  37
  38 /* This handler is called whenever a user switches to this
  39  * virtual console. */
  40 void acquire_vt(int __attribute__((__unused__)) signum) {
  41   /* acknowledge, this is a noop */
  42   ioctl(STDIN_FILENO, VT_RELDISP, VT_ACKACQ);
  43 }
  44
  45 /* Disable console switching while running vlock-current. */
  46 int main(void) {
  47   struct vt_mode vtmode, vtmode_bak;
  48   int pid;
  49   int status;
  50
  51   /* get the virtual console mode */
  52   if (ioctl(STDIN_FILENO, VT_GETMODE, &vtmode) < 0) {
  53     if (errno == ENOTTY || errno == EINVAL)
  54       fprintf(stderr, "vlock-all: this terminal is not a virtual console\n");
  55     else
  56       perror("vlock-all: could not get virtual console mode");
  57
  58     exit (111);
  59   }
  60
  61   /* back up current terminal mode */
  62   vtmode_bak = vtmode;
  63   /* set terminal switching to be process governed */
  64   vtmode.mode = VT_PROCESS;
  65   /* set terminal release signal, i.e. sent when switching away */
  66   vtmode.relsig = SIGUSR1;
  67   /* set terminal acquire signal, i.e. sent when switching here */
  68   vtmode.acqsig = SIGUSR2;
  69   /* set terminal free signal, not implemented on either FreeBSD or Linux */
  70   /* Linux ignores it but FreeBSD wants a valid signal number here */
  71   vtmode.frsig = SIGHUP;
  72
  73   /* set console switching signal handlers */
  74   if (signal(SIGUSR1, release_vt) == SIG_ERR
  75       || signal(SIGUSR2, acquire_vt) == SIG_ERR) {
  76     perror("vlock-all: could not install signal handlers");
  77     exit (111);
  78   }
  79
  80   /* set virtual console mode to be process governed
  81    * thus disabling console switching */
  82   if (ioctl(STDIN_FILENO, VT_SETMODE, &vtmode) < 0) {
  83     perror("vlock-all: could not set virtual console mode");
  84     exit (111);
  85   }
  86
  87   pid = fork();
  88
  89   if (pid == 0) {
  90     /* child */
  91
  92     /* drop privleges */
  93     (void) setuid(getuid());
  94
  95     /* run child */
  96     execl(VLOCK_CURRENT, VLOCK_CURRENT, (char *) NULL);
  97     perror("vlock-all: exec of vlock-current failed");
  98     _exit(127);
  99   } else if (pid < 0) {
 100     perror("vlock-all: could not create child process");
 101   }
 102
 103   if (pid > 0 && waitpid(pid, &status, 0) < 0) {
 104     perror("vlock-all: child process missing");
 105     pid = -1;
 106   }
 107
 108   /* globally enable virtual console switching */
 109   if (ioctl(STDIN_FILENO, VT_SETMODE, &vtmode_bak) < 0)
 110     perror("vlock-all: could not restore console mode");
 111
 112   /* exit with the exit status of the child or 128+signal if it was killed */
 113   if (pid > 0) {
 114     if (WIFEXITED(status))
 115       exit (WEXITSTATUS(status));
 116     else if (WIFSIGNALED(status))
 117       exit (128+WTERMSIG(status));
 118   }
 119
 120   return 0;
 121 }