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=1794418954; b=zk4bB84ktkysVYdsXBXSiFPhx2ZMDB/EXU6pYqCstfMo+OwndCupHj2gqH4LAFKo9AAE tas5KIKl1KkzLLe63AWrkCn7kbXM+zzeHGbNPwcF/Zs0j+jSJQrfNcOGjgBGhkFUJV/SB z37i+8qCe5VioTZq1Y6PYZZ24LgpZP1fGMd62Yri/tpWhAHISqs/JG217OBheIJuxHKU4 3HiMFKLUYbUaQ4q+LGIWO25oydwycmSv9EQEWJeAqBEiLwXNqo9w5Ay/Nkwpz+GqCVIaf dwDiGnw/th3X5qDCMBCRhuNzjdviiZxzw7KfTt/hMba5fMTDlyxi/exCC0B3+Kpi1IQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794418954; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=e6WV4bEOMdGaLgykuWQR1DUk10it+TEyBoO7WMaHPSo=; b=wq12+4+Vu7/26v3QDWBrIS+vwYWQ/yZkprJRI2MXk8CKvsCAS+mNuOYM/X/pelKayiwy q19CIliB7rtSiEsVeX8f7Vg8U2w3akZ/jifrtDTR1u3CaH4qzdNp7+pI2aBmdstR/rCob ayRO4MjhxAMijTdiDXw1x30JmK9r2sthhDK7HcB1c6cDLNahX8tfustGUAYURMSFUUXq6 1NTjo66g1wL4mSJZdJV6Qnk2GB83MF1t4p2z96mq61T4nzOEtohso9HOFv/qi77YIHTqs Hyecz5mikaS7/u891PWY0p9JMALR5jP8EI+85GdF1dHpMyJpCtL606j6eFsGXz+LkZw== 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=kVBZdIgG; 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 3639960A2621 for ; Wed, 11 Nov 2026 17:42:34 +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=kVBZdIgG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 51D7B1F00A0F; Wed, 11 Nov 2026 17:42:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794418953; bh=e6WV4bEOMdGaLgykuWQR1DUk10it+TEyBoO7WMaHPSo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kVBZdIgGJth7xfgmjXEIKAp/VK/G1pZXS8jhRdmBPFsimA767TIxa9XzOdB2kcEUl lon4q62knBQBhqbYwIrYRBaF1od0UELJ5JDw7A3MiIZixWn61Bz4GIqpfm45uLHA9r Oi6CNbsBGO6R+4nhmn6r4coMKlbwQNdgp/onTUt3mcyw+iyaS4kdnYPPD0OVIdo6MG 0OvJvVuTP1rdH0y4cYZ5BNkGEbGb6+g18l3vDgPSWjc+DquRqvOOyYHk5Au0dHjeQR 6CE4eEOUkcZjlmG8F+G8ZtAt9mIOtkpPysQHhQUC730G4QxliAGOMOovZz4NYwYA1g UhWhxBE8MclHg== From: Sasha Levin To: stable@vger.kernel.org Cc: Henrik Enquist , Pavel Hofman , Takashi Iwai , Sasha Levin Subject: [PATCH 6.12.y 2/2] ALSA: aloop: Don't constrain playback params in notify mode Date: Wed, 11 Nov 2026 12:42:31 -0500 Message-ID: <20261111174210.3657227-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111174210.3657227-1-sashal@kernel.org> References: <20261107051902-failed-6.12-ded106036984@kernel.org> <20261111174210.3657227-1-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 24ab1a7fd773d..94ea73b3869c9 100644 --- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -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; } -- 2.53.0