Run authentification in different process

When having i3bar in “hide” mode, it could previously be brought up
while the authentication was running. This is not 100% fixed with this
change, but a lot better, as the normal “raise i3lock to the top”
behavior is not blocked now anymore.

fixes #895

i3lock.c

@@ -22,6 +22,7 @@
 #include <string.h>
 #include <ev.h>
 #include <sys/mman.h>
+#include <sys/wait.h>
 #include <X11/XKBlib.h>
 #include <X11/extensions/XKBfile.h>
 #include <xkbcommon/xkbcommon.h>
@@ -199,27 +200,11 @@ static void clear_input(void) {
     unlock_state = STATE_KEY_PRESSED;
 }
 
-static void input_done(void) {
-    if (clear_pam_wrong_timeout) {
-        ev_timer_stop(main_loop, clear_pam_wrong_timeout);
-        free(clear_pam_wrong_timeout);
-        clear_pam_wrong_timeout = NULL;
-    }
-
-    pam_state = STATE_PAM_VERIFY;
-    redraw_screen();
-
-    if (pam_authenticate(pam_handle, 0) == PAM_SUCCESS) {
-        DEBUG("successfully authenticated\n");
-        clear_password_memory();
-        exit(0);
-    }
-
+static void auth_failed(void) {
     if (debug_mode)
         fprintf(stderr, "Authentication failure\n");
 
     pam_state = STATE_PAM_WRONG;
-    clear_input();
     redraw_screen();
 
     /* Clear this state after 2 seconds (unless the user enters another
@@ -241,6 +226,54 @@ static void input_done(void) {
     }
 }
 
+static void child_cb(EV_P_ ev_child *child_watcher, int revents) {
+    if (child_watcher->rstatus != 0) {
+        DEBUG("Authentication successfull\n");
+        clear_password_memory();
+
+        exit(0);
+    } else {
+        auth_failed();
+    }
+    ev_child_stop(main_loop, child_watcher);
+    free(child_watcher);
+}
+
+static void input_done(void) {
+    if (pam_state == STATE_PAM_VERIFY) {
+        return;
+    }
+
+    if (clear_pam_wrong_timeout) {
+        ev_timer_stop(main_loop, clear_pam_wrong_timeout);
+        free(clear_pam_wrong_timeout);
+        clear_pam_wrong_timeout = NULL;
+    }
+
+    pam_state = STATE_PAM_VERIFY;
+    redraw_screen();
+
+    /* fork to unblock pam_authenticate */
+    pid_t cpid = fork();
+    if (cpid == 0) {
+        exit(pam_authenticate(pam_handle, 0) == PAM_SUCCESS);
+    } else if (cpid > 0) {
+        clear_input();
+        struct ev_child *child_watcher = calloc(sizeof(struct ev_io), 1);
+        ev_child_init(child_watcher, child_cb, cpid, 0);
+        ev_child_set(child_watcher, cpid, 0);
+        ev_child_start(EV_DEFAULT_ child_watcher);
+    } else if (cpid < 0) {
+        DEBUG("Could not fork");
+        if (pam_authenticate(pam_handle, 0) == PAM_SUCCESS) {
+            DEBUG("successfully authenticated\n");
+            clear_password_memory();
+            exit(0);
+        }
+        auth_failed();
+    }
+}
+
 /*
  * Called when the user releases a key. We need to leave the Mode_switch
  * state when the user releases the Mode_switch key.