From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794420534; b=Kt8Fh9gXFuZuELUTr84QmHPXEjCiCbfv6oyr85QpA6jUDHelpJZJcqiTO3iQyJP+YB0o vcAZlNMPuQUqTQeEvBm+386uIQwtJarxgKzTFGcB6T51YNOFPi3iuMQVVgHjThsky9rw0 WpKHwId9YFye4BIJxQZSkuiKZ2HGv2iz54nZoTmjLa1xEY7+dJybk2f//1oOX7hdhphuP OJ0IqBJ5oK9h6P9B+DoVor1CfbxCYN/AnynWJDypjmBoO38DMwK+TZcaFkvlzRqa3OnEy zchtEgtumTfK/1A3sne9j/MhDlTyXhfduIOq1D0trH7jX9ttKtZDtXhoKF1ciG9mLGQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794420534; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=U0gyj2a8XlEB3Koh9HkxkuEE0PBRiHK2iZJInBWgPso=; b=sukTf4r431R7aOO4ib1DC5VtYZW/my+4HwnkQFtkq5HMKLCWTw0EhnZ0ZUutfB+AGgHd +GtRvkQP4EusW+HRd861FkRflroN9im6dvWvREp4fipVdOkdw97C2nAgwWcmI6nLQICI4 YOKSahISNRWdOIje4FbvBwbFcjpeoA2Gwmxgsk0mMCCKEaU8np4SL7UclcuYkNVs5nSW5 HKBry+gSSZ0gfaaYhk0vqyMKYmTlzdPGjmLfoJY3SNttTmaa6ixU27tj2Ff5bhVOJ01qP 8Nj+1BNbz81z5doY6VLvWfroyMH4OsnanYkOqmJllslEM2k8/iFvAd3c4fFfnujwLWA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=eQM2J5d8; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4DB85606A32A for ; Wed, 11 Nov 2026 18:08:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=eQM2J5d8 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9457B1F00A08; Wed, 11 Nov 2026 18:08:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794420534; bh=U0gyj2a8XlEB3Koh9HkxkuEE0PBRiHK2iZJInBWgPso=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eQM2J5d8qwv7mdF9sLI1MtZGVmF3mIvxSOUuiaNeJeqoYILXuxblI5YPeI3MrNRHg +Tl8tmkxgdvEGmQpMDcuAnTou/YJWQOqSS++/V3+EDoBAVNgEoOyEuqNpRId9jqYH5 yd47/HWTcUlki9tYqfHVaY9dhZjEC+aVJBGjR6dYnjMpdy7l30rLTdIc1jXILulnTf Kve8VH11XEXM86PAb31d16StcdMKTpwdD8ImtAlCIZ2HK00O/LwapnoIUbQCMfT5Je qj6IhYp4mC5KVmNc0ifOPwm4+s0s7at+izpSdmCiadJRVsmzm1sk0fXBKT2zviEmw2 +YBH00Rf2zS/w== From: Sasha Levin To: stable@vger.kernel.org Cc: Henrik Enquist , Pavel Hofman , Takashi Iwai , Sasha Levin Subject: [PATCH 6.1.y 2/2] ALSA: aloop: Don't constrain playback params in notify mode Date: Wed, 11 Nov 2026 13:08:51 -0500 Message-ID: <20261111180831.3732596-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111180831.3732596-1-sashal@kernel.org> References: <20261107054422-failed-6.1-ded106036984@kernel.org> <20261111180831.3732596-1-sashal@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Henrik Enquist [ 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 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 Signed-off-by: Takashi Iwai Link: https://patch.msgid.link/20261003-aloop-notify-fix-v1-1-ba5dfb831bf5@gmail.com Signed-off-by: Sasha Levin --- 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