linux-kernel - [PATCH v2] usb: gadget: u_audio: Fix race condition use of controls after free during gadget unbind.

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Date: Thu, 25 Apr 2024 15:18:01 +0000
From: Chris Wulff <Chris.Wulff@...mp.com>
To: "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pavel Hofman
	<pavel.hofman@...tera.com>,
        Julian Scheel <julian@...st.de>,
        Ruslan Bilovol
	<ruslan.bilovol@...il.com>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org"
	<stable@...r.kernel.org>,
        Chris Wulff <chris.wulff@...mp.com>
Subject: [PATCH v2] usb: gadget: u_audio: Fix race condition use of controls
 after free during gadget unbind.


Hang on to the control IDs instead of pointers since those are correctly
handled with locks.

Fixes: 8fe9a03f4331 ("usb: gadget: u_audio: Rate ctl notifies about current srate (0=stopped)")
Fixes: c565ad07ef35 ("usb: gadget: u_audio: Support multiple sampling rates")
Fixes: 02de698ca812 ("usb: gadget: u_audio: add bi-directional volume and mute support")
Signed-off-by: Chris Wulff <chris.wulff@...mp.com>
---
v2: Removed items not directly related to controls. Added Fixes:
v1: https://lore.kernel.org/linux-usb/CO1PR17MB54190B898057616EEB3F9E51E10E2@CO1PR17MB5419.namprd17.prod.outlook.com/

 drivers/usb/gadget/function/u_audio.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index 4a42574b4a7f..c8e8154c59f5 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 */
 
@@ -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);
 }
@@ -807,7 +806,7 @@ 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;
 }
@@ -856,7 +855,7 @@ 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 +1330,7 @@ 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 +1358,7 @@ 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 +1382,7 @@ 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));
-- 
2.34.1