[PATCH] ALSA: hda/cs_dsp_ctl: Use private_free for control cleanup

[PATCH] ALSA: hda/cs_dsp_ctl: Use private_free for control cleanup

[Richard Fitzgerald]

Use the control private_free callback to free the associated data
block. This ensures that the memory won't leak, whatever way the
control gets destroyed.

The original implementation didn't actually remove the ALSA
controls in hda_cs_dsp_control_remove(). It only freed the internal
tracking structure. This meant it was possible to remove/unload the
amp driver while leaving its ALSA controls still present in the
soundcard. Obviously attempting to access them could cause segfaults
or at least dereferencing stale pointers.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 3233b978af23 ("ALSA: hda: hda_cs_dsp_ctl: Add Library to support CS_DSP ALSA controls")
---
This replaces my earlier "keep it simple" attempt at cleanup.
I decided that implementing private_free is the only sensible
way to fix the cleanup.
---
 sound/pci/hda/hda_cs_dsp_ctl.c | 47 ++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/sound/pci/hda/hda_cs_dsp_ctl.c b/sound/pci/hda/hda_cs_dsp_ctl.c
index 463ca06036bf..9db45d7c17e5 100644
--- a/sound/pci/hda/hda_cs_dsp_ctl.c
+++ b/sound/pci/hda/hda_cs_dsp_ctl.c
@@ -8,6 +8,7 @@
 
 #include <linux/module.h>
 #include <sound/soc.h>
+#include <linux/cleanup.h>
 #include <linux/firmware/cirrus/cs_dsp.h>
 #include <linux/firmware/cirrus/wmfw.h>
 #include "hda_cs_dsp_ctl.h"
@@ -97,11 +98,23 @@ static unsigned int wmfw_convert_flags(unsigned int in)
 	return out;
 }
 
-static void hda_cs_dsp_add_kcontrol(struct hda_cs_dsp_coeff_ctl *ctl, const char *name)
+static void hda_cs_dsp_free_kcontrol(struct snd_kcontrol *kctl)
 {
+	struct hda_cs_dsp_coeff_ctl *ctl = (struct hda_cs_dsp_coeff_ctl *)snd_kcontrol_chip(kctl);
 	struct cs_dsp_coeff_ctl *cs_ctl = ctl->cs_ctl;
+
+	/* NULL priv to prevent a double-free in hda_cs_dsp_control_remove() */
+	cs_ctl->priv = NULL;
+	kfree(ctl);
+}
+
+static void hda_cs_dsp_add_kcontrol(struct cs_dsp_coeff_ctl *cs_ctl,
+				    const struct hda_cs_dsp_ctl_info *info,
+				    const char *name)
+{
 	struct snd_kcontrol_new kcontrol = {0};
 	struct snd_kcontrol *kctl;
+	struct hda_cs_dsp_coeff_ctl *ctl __free(kfree) = NULL;
 	int ret = 0;
 
 	if (cs_ctl->len > ADSP_MAX_STD_CTRL_SIZE) {
@@ -110,6 +123,13 @@ static void hda_cs_dsp_add_kcontrol(struct hda_cs_dsp_coeff_ctl *ctl, const char
 		return;
 	}
 
+	ctl = kzalloc(sizeof(*ctl), GFP_KERNEL);
+	if (!ctl)
+		return;
+
+	ctl->cs_ctl = cs_ctl;
+	ctl->card = info->card;
+
 	kcontrol.name = name;
 	kcontrol.info = hda_cs_dsp_coeff_info;
 	kcontrol.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
@@ -117,20 +137,22 @@ static void hda_cs_dsp_add_kcontrol(struct hda_cs_dsp_coeff_ctl *ctl, const char
 	kcontrol.get = hda_cs_dsp_coeff_get;
 	kcontrol.put = hda_cs_dsp_coeff_put;
 
-	/* Save ctl inside private_data, ctl is owned by cs_dsp,
-	 * and will be freed when cs_dsp removes the control */
 	kctl = snd_ctl_new1(&kcontrol, (void *)ctl);
 	if (!kctl)
 		return;
 
-	ret = snd_ctl_add(ctl->card, kctl);
+	kctl->private_free = hda_cs_dsp_free_kcontrol;
+	ctl->kctl = kctl;
+
+	/* snd_ctl_add() calls our private_free on error, which will kfree(ctl) */
+	cs_ctl->priv = no_free_ptr(ctl);
+	ret = snd_ctl_add(info->card, kctl);
 	if (ret) {
 		dev_err(cs_ctl->dsp->dev, "Failed to add KControl %s = %d\n", kcontrol.name, ret);
 		return;
 	}
 
 	dev_dbg(cs_ctl->dsp->dev, "Added KControl: %s\n", kcontrol.name);
-	ctl->kctl = kctl;
 }
 
 static void hda_cs_dsp_control_add(struct cs_dsp_coeff_ctl *cs_ctl,
@@ -138,7 +160,6 @@ static void hda_cs_dsp_control_add(struct cs_dsp_coeff_ctl *cs_ctl,
 {
 	struct cs_dsp *cs_dsp = cs_ctl->dsp;
 	char name[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
-	struct hda_cs_dsp_coeff_ctl *ctl;
 	const char *region_name;
 	int ret;
 
@@ -163,15 +184,7 @@ static void hda_cs_dsp_control_add(struct cs_dsp_coeff_ctl *cs_ctl,
 			 " %.*s", cs_ctl->subname_len - skip, cs_ctl->subname + skip);
 	}
 
-	ctl = kzalloc(sizeof(*ctl), GFP_KERNEL);
-	if (!ctl)
-		return;
-
-	ctl->cs_ctl = cs_ctl;
-	ctl->card = info->card;
-	cs_ctl->priv = ctl;
-
-	hda_cs_dsp_add_kcontrol(ctl, name);
+	hda_cs_dsp_add_kcontrol(cs_ctl, info, name);
 }
 
 void hda_cs_dsp_add_controls(struct cs_dsp *dsp, const struct hda_cs_dsp_ctl_info *info)
@@ -203,7 +216,9 @@ void hda_cs_dsp_control_remove(struct cs_dsp_coeff_ctl *cs_ctl)
 {
 	struct hda_cs_dsp_coeff_ctl *ctl = cs_ctl->priv;
 
-	kfree(ctl);
+	/* ctl and kctl may already have been removed by ALSA private_free */
+	if (ctl && ctl->kctl)
+		snd_ctl_remove(ctl->card, ctl->kctl);
 }
 EXPORT_SYMBOL_NS_GPL(hda_cs_dsp_control_remove, SND_HDA_CS_DSP_CONTROLS);
 
-- 
2.39.2

Re: [PATCH] ALSA: hda/cs_dsp_ctl: Use private_free for control cleanup

[Takashi Iwai]

On Wed, 08 May 2024 11:56:27 +0200,
Richard Fitzgerald wrote:
> 
> Use the control private_free callback to free the associated data
> block. This ensures that the memory won't leak, whatever way the
> control gets destroyed.
> 
> The original implementation didn't actually remove the ALSA
> controls in hda_cs_dsp_control_remove(). It only freed the internal
> tracking structure. This meant it was possible to remove/unload the
> amp driver while leaving its ALSA controls still present in the
> soundcard. Obviously attempting to access them could cause segfaults
> or at least dereferencing stale pointers.
> 
> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
> Fixes: 3233b978af23 ("ALSA: hda: hda_cs_dsp_ctl: Add Library to support CS_DSP ALSA controls")
> ---
> This replaces my earlier "keep it simple" attempt at cleanup.
> I decided that implementing private_free is the only sensible
> way to fix the cleanup.

Applied now.  Thanks.


Takashi