Input: keyboard - fix lack of locking when traversing handler->h_list

Keyboard handler should not attempt to traverse handler->h_list on
its own, without any locking, otherwise it races with registering
and unregistering of input handles which leads to crashes.

Introduce input_handler_for_each_handle() helper that allows safely
iterate over all handles attached to a particular handler and switch
keyboard handler to use it.

Reported-by: Jim Paradis <jparadis@redhat.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 35 insertions, 2 deletions

diff --git a/drivers/input/input.c b/drivers/input/input.c
index cc763c9..5d6421b 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -1651,6 +1651,38 @@ void input_unregister_handler(struct input_handler *handler)
 EXPORT_SYMBOL(input_unregister_handler);
 
 /**
+ * input_handler_for_each_handle - handle iterator
+ * @handler: input handler to iterate
+ * @data: data for the callback
+ * @fn: function to be called for each handle
+ *
+ * Iterate over @bus's list of devices, and call @fn for each, passing
+ * it @data and stop when @fn returns a non-zero value. The function is
+ * using RCU to traverse the list and therefore may be usind in atonic
+ * contexts. The @fn callback is invoked from RCU critical section and
+ * thus must not sleep.
+ */
+int input_handler_for_each_handle(struct input_handler *handler, void *data,
+				  int (*fn)(struct input_handle *, void *))
+{
+	struct input_handle *handle;
+	int retval = 0;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(handle, &handler->h_list, h_node) {
+		retval = fn(handle, data);
+		if (retval)
+			break;
+	}
+
+	rcu_read_unlock();
+
+	return retval;
+}
+EXPORT_SYMBOL(input_handler_for_each_handle);
+
+/**
  * input_register_handle - register a new input handle
  * @handle: handle to register
  *
@@ -1683,7 +1715,7 @@ int input_register_handle(struct input_handle *handle)
 	 * we can't be racing with input_unregister_handle()
 	 * and so separate lock is not needed here.
 	 */
-	list_add_tail(&handle->h_node, &handler->h_list);
+	list_add_tail_rcu(&handle->h_node, &handler->h_list);
 
 	if (handler->start)
 		handler->start(handle);
@@ -1706,7 +1738,7 @@ void input_unregister_handle(struct input_handle *handle)
 {
 	struct input_dev *dev = handle->dev;
 
-	list_del_init(&handle->h_node);
+	list_del_rcu(&handle->h_node);
 
 	/*
 	 * Take dev->mutex to prevent race with input_release_device().
@@ -1714,6 +1746,7 @@ void input_unregister_handle(struct input_handle *handle)
 	mutex_lock(&dev->mutex);
 	list_del_rcu(&handle->d_node);
 	mutex_unlock(&dev->mutex);
+
 	synchronize_rcu();
 }
 EXPORT_SYMBOL(input_unregister_handle);