[PATCH] usb: gadget: u_audio: Fix race condition use of controls after free during gadget unbind.

[Chris Wulff <Chris.Wulff@xxxxxxxxx>]

Hang on to the control IDs instead of pointers since those are correctly handled with locks.
Prevent use of the uac data structure after it has been freed.
Mark the endpoint as disabled sooner so that freed requests aren't used.

Signed-off-by: Chris Wulff <chris.wulff@xxxxxxxxx>
---
 drivers/usb/gadget/function/u_audio.c | 31 ++++++++++++++++-----------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index 4a42574b4a7f..bcae95472455 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -57,13 +57,13 @@ struct uac_rtd_params {
 
   /* Volume/Mute controls and their state */
   int fu_id; /* Feature Unit ID */
-  struct snd_kcontrol *snd_kctl_volume;
-  struct snd_kcontrol *snd_kctl_mute;
+  struct snd_ctl_elem_id snd_kctl_volume_id;
+  struct snd_ctl_elem_id snd_kctl_mute_id;
   s16 volume_min, volume_max, volume_res;
   s16 volume;
   int mute;
 
-	struct snd_kcontrol *snd_kctl_rate; /* read-only current rate */
+	struct snd_ctl_elem_id snd_kctl_rate_id; /* read-only current rate */
 	int srate; /* selected samplerate */
 	int active; /* playback/capture running */
 
@@ -447,6 +447,8 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 	if (!prm->ep_enabled)
 		return;
 
+	prm->ep_enabled = false;
+
 	audio_dev = uac->audio_dev;
 	params = &audio_dev->params;
 
@@ -464,8 +466,6 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 		}
 	}
 
-	prm->ep_enabled = false;
-
 	if (usb_ep_disable(ep))
 		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }
@@ -494,14 +494,13 @@ static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
 static void set_active(struct uac_rtd_params *prm, bool active)
 {
 	// notifying through the Rate ctrl
-	struct snd_kcontrol *kctl = prm->snd_kctl_rate;
 	unsigned long flags;
 
 	spin_lock_irqsave(&prm->lock, flags);
 	if (prm->active != active) {
 		prm->active = active;
 		snd_ctl_notify(prm->uac->card, SNDRV_CTL_EVENT_MASK_VALUE,
-				&kctl->id);
+				&prm->snd_kctl_rate_id);
 	}
 	spin_unlock_irqrestore(&prm->lock, flags);
 }
@@ -792,6 +791,9 @@ int u_audio_set_volume(struct g_audio *audio_dev, int playback, s16 val)
 	unsigned long flags;
 	int change = 0;
 
+	if (!uac)
+		return 0;
+
 	if (playback)
 		prm = &uac->p_prm;
 	else
@@ -807,7 +809,7 @@ int u_audio_set_volume(struct g_audio *audio_dev, int playback, s16 val)
 
 	if (change)
 		snd_ctl_notify(uac->card, SNDRV_CTL_EVENT_MASK_VALUE,
-				&prm->snd_kctl_volume->id);
+				&prm->snd_kctl_volume_id);
 
 	return 0;
 }
@@ -840,6 +842,9 @@ int u_audio_set_mute(struct g_audio *audio_dev, int playback, int val)
 	int change = 0;
 	int mute;
 
+	if (!uac)
+		return 0;
+
 	if (playback)
 		prm = &uac->p_prm;
 	else
@@ -856,7 +861,7 @@ int u_audio_set_mute(struct g_audio *audio_dev, int playback, int val)
 
 	if (change)
 		snd_ctl_notify(uac->card, SNDRV_CTL_EVENT_MASK_VALUE,
-			       &prm->snd_kctl_mute->id);
+			       &prm->snd_kctl_mute_id);
 
 	return 0;
 }
@@ -1331,7 +1336,7 @@ int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
 			err = snd_ctl_add(card, kctl);
 			if (err < 0)
 				goto snd_fail;
-			prm->snd_kctl_mute = kctl;
+			prm->snd_kctl_mute_id = kctl->id;
 			prm->mute = 0;
 		}
 
@@ -1359,7 +1364,7 @@ int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
 			err = snd_ctl_add(card, kctl);
 			if (err < 0)
 				goto snd_fail;
-			prm->snd_kctl_volume = kctl;
+			prm->snd_kctl_volume_id = kctl->id;
 			prm->volume = fu->volume_max;
 			prm->volume_max = fu->volume_max;
 			prm->volume_min = fu->volume_min;
@@ -1383,7 +1388,7 @@ int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
 		err = snd_ctl_add(card, kctl);
 		if (err < 0)
 			goto snd_fail;
-		prm->snd_kctl_rate = kctl;
+		prm->snd_kctl_rate_id = kctl->id;
 	}
 
 	strscpy(card->driver, card_name, sizeof(card->driver));
@@ -1420,6 +1425,8 @@ void g_audio_cleanup(struct g_audio *g_audio)
 		return;
 
 	uac = g_audio->uac;
+	g_audio->uac = NULL;
+
 	card = uac->card;
 	if (card)
 		snd_card_free_when_closed(card);
-- 
2.34.1