1 /* console_switch.c -- console grabbing 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 #if !defined(__FreeBSD__) && !defined(_GNU_SOURCE)
15 #define _GNU_SOURCE
16 #endif
17
18 #include <stdio.h>
19 #include <stdlib.h>
20 #include <string.h>
21 #include <unistd.h>
22 #include <fcntl.h>
23 #include <sys/ioctl.h>
24 #include <errno.h>
25 #include <signal.h>
26
27 #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
28 #include <sys/consio.h>
29 #else
30 #include <sys/vt.h>
31 #endif
32
33 #include "console_switch.h"
34
35 /* Is console switching currently disabled? */
36 bool console_switch_locked = false;
37
38 /* This handler is called whenever a user tries to
39 * switch away from this virtual console. */
release_vt(int signum)40 static void release_vt(int __attribute__ ((__unused__)) signum)
41 {
42 /* Deny console switch. */
43 (void) ioctl(STDIN_FILENO, VT_RELDISP, 0);
44 }
45
46 /* This handler is called whenever a user switches to this
47 * virtual console. */
acquire_vt(int signum)48 static void acquire_vt(int __attribute__ ((__unused__)) signum)
49 {
50 /* Acknowledge console switch. */
51 (void) ioctl(STDIN_FILENO, VT_RELDISP, VT_ACKACQ);
52 }
53
54 /* Console mode before switching was disabled. */
55 static struct vt_mode vtm;
56 /* Signal actions before console handling was disabled. */
57 static struct sigaction sa_usr1;
58 static struct sigaction sa_usr2;
59
60 /* Disable virtual console switching in the kernel. If disabling fails false
61 * is returned and errno is set. */
lock_console_switch(void)62 bool lock_console_switch(void)
63 {
64 /* Console mode when switching is disabled. */
65 struct vt_mode lock_vtm;
66 struct sigaction sa;
67
68 /* Get the virtual console mode. */
69 if (ioctl(STDIN_FILENO, VT_GETMODE, &vtm) < 0) {
70 if (errno == ENOTTY || errno == EINVAL)
71 fprintf(stderr, "vlock: this terminal is not a virtual console\n");
72 else
73 perror("vlock: could not get virtual console mode");
74
75 errno = 0;
76 return false;
77 }
78
79 /* Copy the current virtual console mode. */
80 lock_vtm = vtm;
81
82 (void) sigemptyset(&(sa.sa_mask));
83 sa.sa_flags = SA_RESTART;
84 sa.sa_handler = release_vt;
85 (void) sigaction(SIGUSR1, &sa, &sa_usr1);
86 sa.sa_handler = acquire_vt;
87 (void) sigaction(SIGUSR2, &sa, &sa_usr2);
88
89 /* Set terminal switching to be process governed. */
90 lock_vtm.mode = VT_PROCESS;
91 /* Set terminal release signal, i.e. sent when switching away. */
92 lock_vtm.relsig = SIGUSR1;
93 /* Set terminal acquire signal, i.e. sent when switching here. */
94 lock_vtm.acqsig = SIGUSR2;
95 /* Set terminal free signal, not implemented on either FreeBSD or Linux. */
96 /* Linux ignores this but FreeBSD wants a valid signal number here. */
97 lock_vtm.frsig = SIGHUP;
98
99 /* Set virtual console mode to be process governed thus disabling console
100 * switching through the signal handlers above. */
101 if (ioctl(STDIN_FILENO, VT_SETMODE, &lock_vtm) < 0) {
102 perror("vlock: disabling console switching failed");
103
104 /* Reset signal handlers. */
105 (void) sigaction(SIGUSR1, &sa_usr1, NULL);
106 (void) sigaction(SIGUSR2, &sa_usr2, NULL);
107 errno = 0;
108 return false;
109 }
110
111 console_switch_locked = true;
112 return true;
113 }
114
115 /* Reenable console switching if it was previously disabled. */
unlock_console_switch(void)116 bool unlock_console_switch(void)
117 {
118 if (ioctl(STDIN_FILENO, VT_SETMODE, &vtm) == 0) {
119 /* Reset signal handlers. */
120 (void) sigaction(SIGUSR1, &sa_usr1, NULL);
121 (void) sigaction(SIGUSR2, &sa_usr2, NULL);
122
123 return true;
124 } else {
125 perror("vlock: reenabling console switch failed");
126 errno = 0;
127 return false;
128 }
129 }
130