Input: do not pass injected events back to the originating handler

Sometimes input handlers (as opposed to input devices) have a need to
inject (or re-inject) events back into input core. For example sysrq
filter may want to inject previously suppressed Alt-SysRq so that user
can take a screen print. In this case we do not want to pass such events
back to the same same handler that injected them to avoid loops.

Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/input.c

···
  * dev->event_lock held and interrupts disabled.
  */
 static void input_pass_event(struct input_dev *dev,
+			     struct input_handler *src_handler,
 			     unsigned int type, unsigned int code, int value)
 {
 	struct input_handler *handler;
···
 				continue;
 
 			handler = handle->handler;
+
+			/*
+			 * If this is the handler that injected this
+			 * particular event we want to skip it to avoid
+			 * filters firing again and again.
+			 */
+			if (handler == src_handler)
+				continue;
+
 			if (!handler->filter) {
 				if (filtered)
 					break;
···
 	if (test_bit(dev->repeat_key, dev->key) &&
 	    is_event_supported(dev->repeat_key, dev->keybit, KEY_MAX)) {
 
-		input_pass_event(dev, EV_KEY, dev->repeat_key, 2);
+		input_pass_event(dev, NULL, EV_KEY, dev->repeat_key, 2);
 
 		if (dev->sync) {
 			/*
···
 			 * Otherwise assume that the driver will send
 			 * SYN_REPORT once it's done.
 			 */
-			input_pass_event(dev, EV_SYN, SYN_REPORT, 1);
+			input_pass_event(dev, NULL, EV_SYN, SYN_REPORT, 1);
 		}
 
 		if (dev->rep[REP_PERIOD])
···
 #define INPUT_PASS_TO_ALL	(INPUT_PASS_TO_HANDLERS | INPUT_PASS_TO_DEVICE)
 
 static int input_handle_abs_event(struct input_dev *dev,
+				  struct input_handler *src_handler,
 				  unsigned int code, int *pval)
 {
 	bool is_mt_event;
···
 	/* Flush pending "slot" event */
 	if (is_mt_event && dev->slot != input_abs_get_val(dev, ABS_MT_SLOT)) {
 		input_abs_set_val(dev, ABS_MT_SLOT, dev->slot);
-		input_pass_event(dev, EV_ABS, ABS_MT_SLOT, dev->slot);
+		input_pass_event(dev, src_handler,
+				 EV_ABS, ABS_MT_SLOT, dev->slot);
 	}
 
 	return INPUT_PASS_TO_HANDLERS;
 }
 
 static void input_handle_event(struct input_dev *dev,
+			       struct input_handler *src_handler,
 			       unsigned int type, unsigned int code, int value)
 {
 	int disposition = INPUT_IGNORE_EVENT;
···
 
 	case EV_ABS:
 		if (is_event_supported(code, dev->absbit, ABS_MAX))
-			disposition = input_handle_abs_event(dev, code, &value);
+			disposition = input_handle_abs_event(dev, src_handler,
+							     code, &value);
 
 		break;
 
···
 		dev->event(dev, type, code, value);
 
 	if (disposition & INPUT_PASS_TO_HANDLERS)
-		input_pass_event(dev, type, code, value);
+		input_pass_event(dev, src_handler, type, code, value);
 }
 
 /**
···
 
 		spin_lock_irqsave(&dev->event_lock, flags);
 		add_input_randomness(type, code, value);
-		input_handle_event(dev, type, code, value);
+		input_handle_event(dev, NULL, type, code, value);
 		spin_unlock_irqrestore(&dev->event_lock, flags);
 	}
 }
···
 		rcu_read_lock();
 		grab = rcu_dereference(dev->grab);
 		if (!grab || grab == handle)
-			input_handle_event(dev, type, code, value);
+			input_handle_event(dev, handle->handler,
+					   type, code, value);
 		rcu_read_unlock();
 
 		spin_unlock_irqrestore(&dev->event_lock, flags);
···
 		for (code = 0; code <= KEY_MAX; code++) {
 			if (is_event_supported(code, dev->keybit, KEY_MAX) &&
 			    __test_and_clear_bit(code, dev->key)) {
-				input_pass_event(dev, EV_KEY, code, 0);
+				input_pass_event(dev, NULL, EV_KEY, code, 0);
 			}
 		}
-		input_pass_event(dev, EV_SYN, SYN_REPORT, 1);
+		input_pass_event(dev, NULL, EV_SYN, SYN_REPORT, 1);
 	}
 }
 
···
 	    !is_event_supported(old_keycode, dev->keybit, KEY_MAX) &&
 	    __test_and_clear_bit(old_keycode, dev->key)) {
 
-		input_pass_event(dev, EV_KEY, old_keycode, 0);
+		input_pass_event(dev, NULL, EV_KEY, old_keycode, 0);
 		if (dev->sync)
-			input_pass_event(dev, EV_SYN, SYN_REPORT, 1);
+			input_pass_event(dev, NULL, EV_SYN, SYN_REPORT, 1);
 	}
 
  out: