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