Add option to lock TTY switching

Makefile.am

@@ -56,3 +56,7 @@ EXTRA_DIST = \
 	LICENSE \
 	README.md \
 	I3LOCK_VERSION
+
+# SUID the executable so it has permissions to lock TTY switching
+install-exec-hook:
+	chmod +s $(DESTDIR)$(bindir)/i3lock$(EXEEXT)

i3lock.1

@@ -28,6 +28,7 @@ i3lock \- improved screen locker
 .RB [\|\-u\|]
 .RB [\|\-e\|]
 .RB [\|\-f\|]
+.RB [\|\-l\|]
 
 .SH DESCRIPTION
 .B i3lock
@@ -106,6 +107,10 @@ your computer with the enter key.
 Show the number of failed attempts, if any.
 
 .TP
+.B \-l, \-\-lock-console
+Lock the console to disable TTY switching (Linux only).
+
+.TP
 .B \-\-debug
 Enables debug logging.
 Note, that this will log the password used for authentication to stdout.

i3lock.c

@@ -40,6 +40,11 @@
 #endif
 #include <xcb/xcb_aux.h>
 #include <xcb/randr.h>
+#if defined(__linux__)
+#include <fcntl.h>
+#include <linux/vt.h>
+#include <sys/ioctl.h>
+#endif
 
 #include "i3lock.h"
 #include "xcb.h"
@@ -866,6 +871,11 @@ int main(int argc, char *argv[]) {
     int ret;
     struct pam_conv conv = {conv_callback, NULL};
 #endif
+#if defined(__linux__)
+    bool lock_tty_switching = false;
+    int term = -1;
+#endif
+
     int curs_choice = CURS_NONE;
     int o;
     int longoptind = 0;
@@ -884,6 +894,7 @@ int main(int argc, char *argv[]) {
         {"ignore-empty-password", no_argument, NULL, 'e'},
         {"inactivity-timeout", required_argument, NULL, 'I'},
         {"show-failed-attempts", no_argument, NULL, 'f'},
+        {"lock-console", no_argument, NULL, 'l'},
         {NULL, no_argument, NULL, 0}};
 
     if ((pw = getpwuid(getuid())) == NULL)
@@ -891,7 +902,7 @@ int main(int argc, char *argv[]) {
     if ((username = pw->pw_name) == NULL)
         errx(EXIT_FAILURE, "pw->pw_name is NULL.\n");
 
-    char *optstring = "hvnbdc:p:ui:teI:f";
+    char *optstring = "hvnbdc:p:ui:teI:fl";
     while ((o = getopt_long(argc, argv, optstring, longopts, &longoptind)) != -1) {
         switch (o) {
             case 'v':
@@ -949,9 +960,16 @@ int main(int argc, char *argv[]) {
             case 'f':
                 show_failed_attempts = true;
                 break;
+            case 'l':
+#if defined(__linux__)
+                lock_tty_switching = true;
+#else
+                errx(EXIT_FAILURE, "TTY switch locking is only supported on Linux.");
+#endif
+                break;
             default:
                 errx(EXIT_FAILURE, "Syntax: i3lock [-v] [-n] [-b] [-d] [-c color] [-u] [-p win|default]"
-                                   " [-i image.png] [-t] [-e] [-I timeout] [-f]");
+                                   " [-i image.png] [-t] [-e] [-I timeout] [-f] [-l]");
         }
     }
 
@@ -1117,6 +1135,21 @@ int main(int argc, char *argv[]) {
     if (main_loop == NULL)
         errx(EXIT_FAILURE, "Could not initialize libev. Bad LIBEV_FLAGS?\n");
 
+#if defined(__linux__)
+
+    /* Lock tty switching */
+    if (lock_tty_switching) {
+        if ((term = open("/dev/console", O_RDWR)) == -1) {
+            perror("error locking TTY switching: opening console failed");
+        }
+
+        if (term != -1 && (ioctl(term, VT_LOCKSWITCH)) == -1) {
+            perror("error locking TTY switching: locking console failed");
+        }
+    }
+
+#endif
+
     /* Explicitly call the screen redraw in case "locking…" message was displayed */
     auth_state = STATE_AUTH_IDLE;
     redraw_screen();
@@ -1144,6 +1177,18 @@ int main(int argc, char *argv[]) {
         return 0;
     }
 
+#if defined(__linux__)
+    /* Restore tty switching */
+    if (lock_tty_switching) {
+        if (term != -1 && (ioctl(term, VT_UNLOCKSWITCH)) == -1) {
+            perror("error unlocking TTY switching: unlocking console failed");
+        }
+
+        close(term);
+    }
+
+#endif
+
     DEBUG("restoring focus to X11 window 0x%08x\n", stolen_focus);
     xcb_ungrab_pointer(conn, XCB_CURRENT_TIME);
     xcb_ungrab_keyboard(conn, XCB_CURRENT_TIME);