FAILED: patch "[PATCH] ALSA: aloop: Don't constrain playback params in notify mode" failed to apply to 6.1-stable tree

FAILED: patch "[PATCH] ALSA: aloop: Don't constrain playback params in notify mode" failed to apply to 6.1-stable tree

[Sasha Levin]

The patch below does not apply to the 6.1-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 <stable@vger.kernel.org>.

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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x ded106036984a9dd766e7e1451b02e2d15c81438
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107054422-failed-6.1-ded106036984@kernel.org' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Thanks,
Sasha

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

From ded106036984a9dd766e7e1451b02e2d15c81438 Mon Sep 17 00:00:00 2001
From: Henrik Enquist <henrik.enquist@gmail.com>
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 <pavel.hofman@ivitera.com>
Closes: https://lore.kernel.org/all/b4af9071-f8d7-5b47-4d7a-c5743bd67394@ivitera.com/
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Henrik Enquist <henrik.enquist@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20261003-aloop-notify-fix-v1-1-ba5dfb831bf5@gmail.com
---
 sound/drivers/aloop.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 81cb1f59f703b..5f0e2dc96769e 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -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;
 	}
-- 
2.53.0

[PATCH 6.1.y 1/2] ALSA: aloop: Use guard() for mutex locks

[Sasha Levin]

From: Takashi Iwai <tiwai@suse.de>

[ 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 <tiwai@suse.de>
Link: https://patch.msgid.link/20250829150026.6379-2-tiwai@suse.de

Limit the conversion to the four hardware rules needed by the
notify-mode playback fix. The access-control callbacks are absent,
and the remaining mutex conversions are unnecessary for that fix.
The scoped guards preserve the existing lock boundaries and release
the mutex if a hardware rule returns early.

Stable-dep-of: ded106036984 ("ALSA: aloop: Don't constrain playback params in notify mode")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 sound/drivers/aloop.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 9c7671f034d54..cc0c59232d61f 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -952,10 +952,10 @@ 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);
 }
 
@@ -966,10 +966,10 @@ 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);
@@ -982,10 +982,10 @@ 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);
@@ -998,10 +998,10 @@ 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;
-- 
2.53.0

[PATCH 6.1.y 2/2] ALSA: aloop: Don't constrain playback params in notify mode

[Sasha Levin]

From: Henrik Enquist <henrik.enquist@gmail.com>

[ Upstream commit ded106036984a9dd766e7e1451b02e2d15c81438 ]

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 <pavel.hofman@ivitera.com>
Closes: https://lore.kernel.org/all/b4af9071-f8d7-5b47-4d7a-c5743bd67394@ivitera.com/
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Henrik Enquist <henrik.enquist@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20261003-aloop-notify-fix-v1-1-ba5dfb831bf5@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 sound/drivers/aloop.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index cc0c59232d61f..18ca2951d4be6 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -944,6 +944,18 @@ 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)
 {
@@ -953,6 +965,8 @@ 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);
 	}
@@ -967,6 +981,8 @@ 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;
 	}
@@ -983,6 +999,8 @@ 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;
 	}
@@ -999,6 +1017,8 @@ 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;
 	}
-- 
2.53.0