[PATCH v3] Input: sparse-keymap - use a managed allocation for keymap copy

["Michał Kępień" <kernel@kempniu.pl>]

Some platform drivers use devm_input_allocate_device() together with
sparse_keymap_setup() in their .probe callbacks.  While using the former
simplifies error handling, using the latter necessitates calling
sparse_keymap_free() in the error path and upon module unloading to
avoid leaking the copy of the keymap allocated by sparse_keymap_setup().

To help prevent such leaks and enable simpler error handling, make
sparse_keymap_setup() use devm_kmemdup() to create the keymap copy so
that it gets automatically freed.

This works for both managed and non-managed input devices as the keymap
is freed after the last reference to the input device is dropped.

Note that actions previously taken by sparse_keymap_free(), i.e. taking
the input device's mutex and zeroing its keycode and keycodemax fields,
are now redundant because the managed keymap will always be freed after
the input device is unregistered.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
---
Changes from v2:

  - Always use the input device as the owner of the managed keymap copy,
    no matter whether that input device is itself managed or
    non-managed.

  - Use devm_kmemdup() instead of devm_kcalloc() to avoid a separate
    call to memcpy().

  - Update commit message to reflect the above changes.

Changes from v1:

  - Do not add a new function.  Instead, make sparse_keymap_setup()
    always use a managed allocation, which allows making
    sparse_keymap_free() a noop and simplifies error handling.

  - Update subject, commit message and comments accordingly.

 drivers/input/sparse-keymap.c | 39 +++++++++------------------------------
 1 file changed, 9 insertions(+), 30 deletions(-)

diff --git a/drivers/input/sparse-keymap.c b/drivers/input/sparse-keymap.c
index e7409c45bdd0..12a3ad83296d 100644
--- a/drivers/input/sparse-keymap.c
+++ b/drivers/input/sparse-keymap.c
@@ -160,12 +160,12 @@ static int sparse_keymap_setkeycode(struct input_dev *dev,
  * @keymap: Keymap in form of array of &key_entry structures ending
  *	with %KE_END type entry
  * @setup: Function that can be used to adjust keymap entries
- *	depending on device's deeds, may be %NULL
+ *	depending on device's needs, may be %NULL
  *
  * The function calculates size and allocates copy of the original
  * keymap after which sets up input device event bits appropriately.
- * Before destroying input device allocated keymap should be freed
- * with a call to sparse_keymap_free().
+ * The allocated copy of the keymap is automatically freed when it
+ * is no longer needed.
  */
 int sparse_keymap_setup(struct input_dev *dev,
 			const struct key_entry *keymap,
@@ -180,19 +180,18 @@ int sparse_keymap_setup(struct input_dev *dev,
 	for (e = keymap; e->type != KE_END; e++)
 		map_size++;
 
-	map = kcalloc(map_size, sizeof(struct key_entry), GFP_KERNEL);
+	map = devm_kmemdup(&dev->dev, keymap, map_size * sizeof(*map),
+			   GFP_KERNEL);
 	if (!map)
 		return -ENOMEM;
 
-	memcpy(map, keymap, map_size * sizeof(struct key_entry));
-
 	for (i = 0; i < map_size; i++) {
 		entry = &map[i];
 
 		if (setup) {
 			error = setup(dev, entry);
 			if (error)
-				goto err_out;
+				return error;
 		}
 
 		switch (entry->type) {
@@ -221,10 +220,6 @@ int sparse_keymap_setup(struct input_dev *dev,
 	dev->setkeycode = sparse_keymap_setkeycode;
 
 	return 0;
-
- err_out:
-	kfree(map);
-	return error;
 }
 EXPORT_SYMBOL(sparse_keymap_setup);
 
@@ -232,29 +227,13 @@ EXPORT_SYMBOL(sparse_keymap_setup);
  * sparse_keymap_free - free memory allocated for sparse keymap
  * @dev: Input device using sparse keymap
  *
- * This function is used to free memory allocated by sparse keymap
+ * This function used to free memory allocated by sparse keymap
  * in an input device that was set up by sparse_keymap_setup().
- * NOTE: It is safe to cal this function while input device is
- * still registered (however the drivers should care not to try to
- * use freed keymap and thus have to shut off interrupts/polling
- * before freeing the keymap).
+ * Since sparse_keymap_setup() now uses a managed allocation for the
+ * keymap copy, use of this function is deprecated.
  */
 void sparse_keymap_free(struct input_dev *dev)
 {
-	unsigned long flags;
-
-	/*
-	 * Take event lock to prevent racing with input_get_keycode()
-	 * and input_set_keycode() if we are called while input device
-	 * is still registered.
-	 */
-	spin_lock_irqsave(&dev->event_lock, flags);
-
-	kfree(dev->keycode);
-	dev->keycode = NULL;
-	dev->keycodemax = 0;
-
-	spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 EXPORT_SYMBOL(sparse_keymap_free);
 
-- 
2.12.0