[PATCH v2] ALSA: jack: Access input_dev under mutex

[Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>]

It is possible when using ASoC that input_dev is unregistered while
calling snd_jack_report, which causes NULL pointer dereference.
In order to prevent this serialize access to input_dev using mutex lock.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>
---

Changes:
v2:
 - drop mutex in snd_jack_new
 - add comment that snd_jack_report() should be called in context where
   it can sleep

---
 include/sound/jack.h |  1 +
 sound/core/jack.c    | 34 +++++++++++++++++++++++++++-------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/sound/jack.h b/include/sound/jack.h
index 1181f536557e..1ed90e2109e9 100644
--- a/include/sound/jack.h
+++ b/include/sound/jack.h
@@ -62,6 +62,7 @@ struct snd_jack {
 	const char *id;
 #ifdef CONFIG_SND_JACK_INPUT_DEV
 	struct input_dev *input_dev;
+	struct mutex input_dev_lock;
 	int registered;
 	int type;
 	char name[100];
diff --git a/sound/core/jack.c b/sound/core/jack.c
index d1e3055f2b6a..88493cc31914 100644
--- a/sound/core/jack.c
+++ b/sound/core/jack.c
@@ -42,8 +42,11 @@ static int snd_jack_dev_disconnect(struct snd_device *device)
 #ifdef CONFIG_SND_JACK_INPUT_DEV
 	struct snd_jack *jack = device->device_data;
 
-	if (!jack->input_dev)
+	mutex_lock(&jack->input_dev_lock);
+	if (!jack->input_dev) {
+		mutex_unlock(&jack->input_dev_lock);
 		return 0;
+	}
 
 	/* If the input device is registered with the input subsystem
 	 * then we need to use a different deallocator. */
@@ -52,6 +55,7 @@ static int snd_jack_dev_disconnect(struct snd_device *device)
 	else
 		input_free_device(jack->input_dev);
 	jack->input_dev = NULL;
+	mutex_unlock(&jack->input_dev_lock);
 #endif /* CONFIG_SND_JACK_INPUT_DEV */
 	return 0;
 }
@@ -90,8 +94,11 @@ static int snd_jack_dev_register(struct snd_device *device)
 	snprintf(jack->name, sizeof(jack->name), "%s %s",
 		 card->shortname, jack->id);
 
-	if (!jack->input_dev)
+	mutex_lock(&jack->input_dev_lock);
+	if (!jack->input_dev) {
+		mutex_unlock(&jack->input_dev_lock);
 		return 0;
+	}
 
 	jack->input_dev->name = jack->name;
 
@@ -116,6 +123,7 @@ static int snd_jack_dev_register(struct snd_device *device)
 	if (err == 0)
 		jack->registered = 1;
 
+	mutex_unlock(&jack->input_dev_lock);
 	return err;
 }
 #endif /* CONFIG_SND_JACK_INPUT_DEV */
@@ -517,9 +525,11 @@ int snd_jack_new(struct snd_card *card, const char *id, int type,
 		return -ENOMEM;
 	}
 
-	/* don't creat input device for phantom jack */
-	if (!phantom_jack) {
 #ifdef CONFIG_SND_JACK_INPUT_DEV
+	mutex_init(&jack->input_dev_lock);
+
+	/* don't create input device for phantom jack */
+	if (!phantom_jack) {
 		int i;
 
 		jack->input_dev = input_allocate_device();
@@ -537,8 +547,8 @@ int snd_jack_new(struct snd_card *card, const char *id, int type,
 				input_set_capability(jack->input_dev, EV_SW,
 						     jack_switch_types[i]);
 
-#endif /* CONFIG_SND_JACK_INPUT_DEV */
 	}
+#endif /* CONFIG_SND_JACK_INPUT_DEV */
 
 	err = snd_device_new(card, SNDRV_DEV_JACK, jack, &ops);
 	if (err < 0)
@@ -578,10 +588,14 @@ EXPORT_SYMBOL(snd_jack_new);
 void snd_jack_set_parent(struct snd_jack *jack, struct device *parent)
 {
 	WARN_ON(jack->registered);
-	if (!jack->input_dev)
+	mutex_lock(&jack->input_dev_lock);
+	if (!jack->input_dev) {
+		mutex_unlock(&jack->input_dev_lock);
 		return;
+	}
 
 	jack->input_dev->dev.parent = parent;
+	mutex_unlock(&jack->input_dev_lock);
 }
 EXPORT_SYMBOL(snd_jack_set_parent);
 
@@ -629,6 +643,8 @@ EXPORT_SYMBOL(snd_jack_set_key);
 
 /**
  * snd_jack_report - Report the current status of a jack
+ * Note: This function uses mutexes and should be called from a
+ * context which can sleep (such as a workqueue).
  *
  * @jack:   The jack to report status for
  * @status: The current status of the jack
@@ -654,8 +670,11 @@ void snd_jack_report(struct snd_jack *jack, int status)
 					     status & jack_kctl->mask_bits);
 
 #ifdef CONFIG_SND_JACK_INPUT_DEV
-	if (!jack->input_dev)
+	mutex_lock(&jack->input_dev_lock);
+	if (!jack->input_dev) {
+		mutex_unlock(&jack->input_dev_lock);
 		return;
+	}
 
 	for (i = 0; i < ARRAY_SIZE(jack->key); i++) {
 		int testbit = ((SND_JACK_BTN_0 >> i) & ~mask_bits);
@@ -675,6 +694,7 @@ void snd_jack_report(struct snd_jack *jack, int status)
 	}
 
 	input_sync(jack->input_dev);
+	mutex_unlock(&jack->input_dev_lock);
 #endif /* CONFIG_SND_JACK_INPUT_DEV */
 }
 EXPORT_SYMBOL(snd_jack_report);
-- 
2.25.1