FAILED: patch "[PATCH] ALSA: aloop: Don't constrain playback params in notify mode" failed to apply to 6.12-stable tree

PATCH New Sasha Levin 1 participant 3 messages Nov 7 – Nov 11

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Sasha Levin

author maintainer

2026-11-07 10:19 UTC #0 lore raw

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x ded106036984a9dd766e7e1451b02e2d15c81438
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From ded106036984a9dd766e7e1451b02e2d15c81438 Mon Sep 17 00:00:00 2001
From: Henrik Enquist <[email protected]>
Date: Sat, 3 Oct 2026 15:26:11 +0200
Subject: [PATCH] ALSA: aloop: Don't constrain playback params in notify mode

With notify enabled (the pcm_notify module parameter or the "PCM Notify" control), the playback side of a cable may change format, rate and channels while a capture is running. loopback_check_format() then stops the capture and notifies the "PCM Slave" controls, so that the capture application can reopen with the new parameters. For this reason loopback_open() still gives a notify mode playback the unconstrained loopback_pcm_hardware.

Since commit 898dfe4687f4 ("ALSA: aloop: Fix racy hw constraints adjustment") the hw rules refine against the shared cable->hw instead of the substream's own runtime->hw. This pins the playback side to the parameters of an open capture whatever the notify setting is. A player probing the device sees only the capture's rate, format and channels, and the format change path in loopback_check_format() can't be reached by a new playback.

Skip the format, rate and channels rules for the playback substream when notify is enabled. Skip the period bytes rule as well: with a sound timer source, params_change() already takes the period size from a notify mode playback, and keeping the old capture's period bytes leaves a playback at another rate with a period that doesn't match the timer. The capture side stays constrained to the cable parameters.

The capture stop this makes reachable again was hardened by commit 826af7fa62e3 ("ALSA: aloop: Fix racy access at PCM trigger") and commit e5c33cdc6f40 ("ALSA: aloop: Fix peer runtime UAF during format-change stop"), which need to be applied first when backporting.

Reproducer, with notify enabled on the cable:
arecord -D hw:Loopback,1,0 -r 44100 -f S32_LE -c 2 /dev/null & aplay -D hw:Loopback,0,0 96k.wav
Before: aplay is forced to 44100 Hz and the capture keeps running.
After: aplay runs at 96000 Hz, the capture is stopped and "PCM Slave Rate" reports 96000.

Fixes 898dfe4687f4 ("ALSA: aloop: Fix racy hw constraints adjustment")

Reported-by Pavel Hofman <[email protected]>

Closes https://lore.kernel.org/all/[email protected]/ open here

Cc [email protected]

Assisted-by Claude:claude-opus-5-5

Signed-off-by Henrik Enquist <[email protected]>

Signed-off-by Takashi Iwai <[email protected]>

Link https://patch.msgid.link/[email protected] open here

---
 sound/drivers/aloop.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

sound/drivers/aloop.c +20 -0

index 81cb1f59f703b..5f0e2dc96769e 100644
@@ -1073,6 +1073,18 @@ static unsigned int get_cable_index(struct snd_pcm_substream *substream)
 		return !substream->stream;
 }
 
+/*
+ * In notify mode the playback side may change format, rate, channels and,
+ * with a sound timer, the period size. A running capture that no longer
+ * matches is stopped by loopback_check_format().
+ * call in loopback->cable_lock
+ */
+static bool loopback_playback_unconstrained(struct loopback_pcm *dpcm)
+{
+	return dpcm->substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+	       get_notify(dpcm);
+}
+
 static int rule_format(struct snd_pcm_hw_params *params,
 		       struct snd_pcm_hw_rule *rule)
 {

@@ -1082,6 +1094,8 @@ static int rule_format(struct snd_pcm_hw_params *params,
 
 	snd_mask_none(&m);
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		m.bits[0] = (u_int32_t)cable->hw.formats;
 		m.bits[1] = (u_int32_t)(cable->hw.formats >> 32);
 	}

@@ -1096,6 +1110,8 @@ static int rule_rate(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.rate_min;
 		t.max = cable->hw.rate_max;
 	}

@@ -1112,6 +1128,8 @@ static int rule_channels(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.channels_min;
 		t.max = cable->hw.channels_max;
 	}

@@ -1128,6 +1146,8 @@ static int rule_period_bytes(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.period_bytes_min;
 		t.max = cable->hw.period_bytes_max;
 	}

Signature · 1 line

2.53.0

Sasha Levin

author maintainer

2026-11-11 17:42 UTC #1 lore raw

PATCH 1/2 ALSA: aloop: Use guard() for mutex locks

From: Takashi Iwai <[email protected]>

[ Upstream commit ebd9b6c91d4e345b7ded4b56567c46267a45d961 ]

Replace the manual mutex lock/unlock pairs with guard() for code simplification.

Only code refactoring, and no behavior change.

Signed-off-by Takashi Iwai <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Stable-dep-of: ded106036984 ("ALSA: aloop: Don't constrain playback params in notify mode")

Signed-off-by Sasha Levin <[email protected]>

---
 sound/drivers/aloop.c | 83 +++++++++++++++++--------------------------
 1 file changed, 33 insertions(+), 50 deletions(-)

sound/drivers/aloop.c +33 ~~-50~~

index 50b8e7b3d8179..24ab1a7fd773d 100644
@@ -532,13 +532,12 @@ static int loopback_prepare(struct snd_pcm_substream *substream)
 	dpcm->pcm_salign = salign;
 	dpcm->pcm_period_size = frames_to_bytes(runtime, runtime->period_size);
 
-	mutex_lock(&dpcm->loopback->cable_lock);
+	guard(mutex)(&dpcm->loopback->cable_lock);
 	if (!(cable->valid & ~(1 << substream->stream)) ||
             (get_setup(dpcm)->notify &&
 	     substream->stream == SNDRV_PCM_STREAM_PLAYBACK))
 		params_change(substream);
 	cable->valid |= 1 << substream->stream;
-	mutex_unlock(&dpcm->loopback->cable_lock);
 
 	return 0;
 }

@@ -979,9 +978,8 @@ static int loopback_hw_free(struct snd_pcm_substream *substream)
 	struct loopback_pcm *dpcm = runtime->private_data;
 	struct loopback_cable *cable = dpcm->cable;
 
-	mutex_lock(&dpcm->loopback->cable_lock);
+	guard(mutex)(&dpcm->loopback->cable_lock);
 	cable->valid &= ~(1 << substream->stream);
-	mutex_unlock(&dpcm->loopback->cable_lock);
 	return 0;
 }

@@ -1001,10 +999,10 @@ static int rule_format(struct snd_pcm_hw_params *params,
 	struct snd_mask m;
 
 	snd_mask_none(&m);
-	mutex_lock(&dpcm->loopback->cable_lock);
-	m.bits[0] = (u_int32_t)cable->hw.formats;
-	m.bits[1] = (u_int32_t)(cable->hw.formats >> 32);
-	mutex_unlock(&dpcm->loopback->cable_lock);
+	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		m.bits[0] = (u_int32_t)cable->hw.formats;
+		m.bits[1] = (u_int32_t)(cable->hw.formats >> 32);
+	}
 	return snd_mask_refine(hw_param_mask(params, rule->var), &m);
 }

@@ -1015,10 +1013,10 @@ static int rule_rate(struct snd_pcm_hw_params *params,
 	struct loopback_cable *cable = dpcm->cable;
 	struct snd_interval t;
 
-	mutex_lock(&dpcm->loopback->cable_lock);
-	t.min = cable->hw.rate_min;
-	t.max = cable->hw.rate_max;
-	mutex_unlock(&dpcm->loopback->cable_lock);
+	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		t.min = cable->hw.rate_min;
+		t.max = cable->hw.rate_max;
+	}
         t.openmin = t.openmax = 0;
         t.integer = 0;
 	return snd_interval_refine(hw_param_interval(params, rule->var), &t);

@@ -1031,10 +1029,10 @@ static int rule_channels(struct snd_pcm_hw_params *params,
 	struct loopback_cable *cable = dpcm->cable;
 	struct snd_interval t;
 
-	mutex_lock(&dpcm->loopback->cable_lock);
-	t.min = cable->hw.channels_min;
-	t.max = cable->hw.channels_max;
-	mutex_unlock(&dpcm->loopback->cable_lock);
+	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		t.min = cable->hw.channels_min;
+		t.max = cable->hw.channels_max;
+	}
         t.openmin = t.openmax = 0;
         t.integer = 0;
 	return snd_interval_refine(hw_param_interval(params, rule->var), &t);

@@ -1047,10 +1045,10 @@ static int rule_period_bytes(struct snd_pcm_hw_params *params,
 	struct loopback_cable *cable = dpcm->cable;
 	struct snd_interval t;
 
-	mutex_lock(&dpcm->loopback->cable_lock);
-	t.min = cable->hw.period_bytes_min;
-	t.max = cable->hw.period_bytes_max;
-	mutex_unlock(&dpcm->loopback->cable_lock);
+	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		t.min = cable->hw.period_bytes_min;
+		t.max = cable->hw.period_bytes_max;
+	}
 	t.openmin = 0;
 	t.openmax = 0;
 	t.integer = 0;

@@ -1264,12 +1262,10 @@ static int loopback_open(struct snd_pcm_substream *substream)
 	int err = 0;
 	int dev = get_cable_index(substream);
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL);
-	if (!dpcm) {
-		err = -ENOMEM;
-		goto unlock;
-	}
+	if (!dpcm)
+		return -ENOMEM;
 	dpcm->loopback = loopback;
 	dpcm->substream = substream;

@@ -1354,7 +1350,6 @@ static int loopback_open(struct snd_pcm_substream *substream)
 		free_cable(substream);
 		kfree(dpcm);
 	}
-	mutex_unlock(&loopback->cable_lock);
 	return err;
 }

@@ -1366,9 +1361,8 @@ static int loopback_close(struct snd_pcm_substream *substream)
 
 	if (dpcm->cable->ops->close_substream)
 		err = dpcm->cable->ops->close_substream(dpcm);
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	free_cable(substream);
-	mutex_unlock(&loopback->cable_lock);
 	return err;
 }

@@ -1419,11 +1413,10 @@ static int loopback_rate_shift_get(struct snd_kcontrol *kcontrol,
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].rate_shift;
-	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }

@@ -1439,14 +1432,13 @@ static int loopback_rate_shift_put(struct snd_kcontrol *kcontrol,
 		val = 80000;
 	if (val > 120000)
 		val = 120000;	
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	if (val != loopback->setup[kcontrol->id.subdevice]
 				  [kcontrol->id.device].rate_shift) {
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].rate_shift = val;
 		change = 1;
 	}
-	mutex_unlock(&loopback->cable_lock);
 	return change;
 }

@@ -1455,11 +1447,10 @@ static int loopback_notify_get(struct snd_kcontrol *kcontrol,
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].notify;
-	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }

@@ -1471,14 +1462,13 @@ static int loopback_notify_put(struct snd_kcontrol *kcontrol,
 	int change = 0;
 
 	val = ucontrol->value.integer.value[0] ? 1 : 0;
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	if (val != loopback->setup[kcontrol->id.subdevice]
 				[kcontrol->id.device].notify) {
 		loopback->setup[kcontrol->id.subdevice]
 			[kcontrol->id.device].notify = val;
 		change = 1;
 	}
-	mutex_unlock(&loopback->cable_lock);
 	return change;
 }

@@ -1490,14 +1480,13 @@ static int loopback_active_get(struct snd_kcontrol *kcontrol,
 
 	unsigned int val = 0;
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	cable = loopback->cables[kcontrol->id.subdevice][kcontrol->id.device ^ 1];
 	if (cable != NULL) {
 		unsigned int running = cable->running ^ cable->pause;
 
 		val = (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ? 1 : 0;
 	}
-	mutex_unlock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] = val;
 	return 0;
 }

@@ -1540,11 +1529,10 @@ static int loopback_rate_get(struct snd_kcontrol *kcontrol,
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].rate;
-	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }

@@ -1564,11 +1552,10 @@ static int loopback_channels_get(struct snd_kcontrol *kcontrol,
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].channels;
-	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }

@@ -1586,12 +1573,11 @@ static int loopback_access_get(struct snd_kcontrol *kcontrol,
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	snd_pcm_access_t access;
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	access = loopback->setup[kcontrol->id.subdevice][kcontrol->id.device].access;
 
 	ucontrol->value.enumerated.item[0] = !is_access_interleaved(access);
 
-	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }

@@ -1759,12 +1745,11 @@ static void print_cable_info(struct snd_info_entry *entry,
 	struct loopback *loopback = entry->private_data;
 	int sub, num;
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	num = entry->name[strlen(entry->name)-1];
 	num = num == '0' ? 0 : 1;
 	for (sub = 0; sub < MAX_PCM_SUBSTREAMS; sub++)
 		print_substream_info(buffer, loopback, sub, num);
-	mutex_unlock(&loopback->cable_lock);
 }
 
 static int loopback_cable_proc_new(struct loopback *loopback, int cidx)

@@ -1793,10 +1778,9 @@ static void print_timer_source_info(struct snd_info_entry *entry,
 {
 	struct loopback *loopback = entry->private_data;
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	snd_iprintf(buffer, "%s\n",
 		    loopback->timer_source ? loopback->timer_source : "");
-	mutex_unlock(&loopback->cable_lock);
 }
 
 static void change_timer_source_info(struct snd_info_entry *entry,

@@ -1805,10 +1789,9 @@ static void change_timer_source_info(struct snd_info_entry *entry,
 	struct loopback *loopback = entry->private_data;
 	char line[64];
 
-	mutex_lock(&loopback->cable_lock);
+	guard(mutex)(&loopback->cable_lock);
 	if (!snd_info_get_line(buffer, line, sizeof(line)))
 		loopback_set_timer_source(loopback, strim(line));
-	mutex_unlock(&loopback->cable_lock);
 }
 
 static int loopback_timer_source_proc_new(struct loopback *loopback)

Signature · 1 line

2.53.0

Sasha Levin

author maintainer

2026-11-11 17:42 UTC #2 lore raw

PATCH 2/2 ALSA: aloop: Don't constrain playback params in notify mode

From: Henrik Enquist <[email protected]>

[ Upstream commit ded106036984a9dd766e7e1451b02e2d15c81438 ]

Fixes 898dfe4687f4 ("ALSA: aloop: Fix racy hw constraints adjustment")

Reported-by Pavel Hofman <[email protected]>

Closes https://lore.kernel.org/all/[email protected]/ open here

Cc [email protected]

Assisted-by Claude:claude-opus-5-5

Signed-off-by Henrik Enquist <[email protected]>

Signed-off-by Takashi Iwai <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Sasha Levin <[email protected]>

---
 sound/drivers/aloop.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

sound/drivers/aloop.c +20 -0

index 24ab1a7fd773d..94ea73b3869c9 100644
@@ -991,6 +991,18 @@ static unsigned int get_cable_index(struct snd_pcm_substream *substream)
 		return !substream->stream;
 }
 
+/*
+ * In notify mode the playback side may change format, rate, channels and,
+ * with a sound timer, the period size. A running capture that no longer
+ * matches is stopped by loopback_check_format().
+ * call in loopback->cable_lock
+ */
+static bool loopback_playback_unconstrained(struct loopback_pcm *dpcm)
+{
+	return dpcm->substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+	       get_notify(dpcm);
+}
+
 static int rule_format(struct snd_pcm_hw_params *params,
 		       struct snd_pcm_hw_rule *rule)
 {

@@ -1000,6 +1012,8 @@ static int rule_format(struct snd_pcm_hw_params *params,
 
 	snd_mask_none(&m);
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		m.bits[0] = (u_int32_t)cable->hw.formats;
 		m.bits[1] = (u_int32_t)(cable->hw.formats >> 32);
 	}

@@ -1014,6 +1028,8 @@ static int rule_rate(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.rate_min;
 		t.max = cable->hw.rate_max;
 	}

@@ -1030,6 +1046,8 @@ static int rule_channels(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.channels_min;
 		t.max = cable->hw.channels_max;
 	}

@@ -1046,6 +1064,8 @@ static int rule_period_bytes(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 
 	scoped_guard(mutex, &dpcm->loopback->cable_lock) {
+		if (loopback_playback_unconstrained(dpcm))
+			return 0;
 		t.min = cable->hw.period_bytes_min;
 		t.max = cable->hw.period_bytes_max;
 	}

Signature · 1 line

2.53.0