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=1794419732; b=tE27AFCyPTwwkpgt1F64GoNHIGy1/vbbDhX7VrMD3CtewvqpiZmB3A10whj5sZG+ypq4 PqMopr9MlYzkYZSlwsWHaO+zi61Ypisy3RXiHGm/W5Beuy3CCYBYnHFKDitSG/iRroCrR iYMPvJMmrEukwCtmWxYXIv6PYKUZBQK9NK7DcImeLuISZMu38OoovmTC8YDDdvYmSu8q9 moVYwai1WZD05zt99pD14JN2s/8Z3ALi+JQSB81hIxNl1guwl+G+b6BAWa1b3y9dbYyMg NqPxL/BpIzQYUc1nXmPBcHd/AAA48OQxpWpWylM2SSiu2NElHSbJhfoKhcUoDjMDAZQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794419732; 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=5bnghHcToQNXC1ne+QdW+au8k/3qXkewkhGz+eWJ0EA2pjXOmvu7aokoEAoF3zbJVaHH ucm+nmyFDuNfEqgWCXnhKptPy1JnjII3gEExYTEOHIfby6Vzn0C7U49HipK7ZClOxSfTS i+5FEdMrlAaybCNWPVxJxCOyjA8g8RvLQeNlQn1h9QnhASWpbVrGk/gKNLu/nA8T8uKQg pqXI73c2uwIrdnSHARFh4Lbjs39gD8HYbuUtFlh+RKN/Ia98u/nSsvidF6AvkNJTXCysd BilCN1EhI7przBiHn6Zr8sdoSZeZdPrjDMfRtG329zhyreC/4rabVFMujerPUgH8uHA== 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="UKYp/v6N"; 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 9BF9A606A321 for ; Wed, 11 Nov 2026 17:55:32 +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=UKYp/v6N Received: by smtp.kernel.org (Postfix) with ESMTPSA id E775E1F00A06; Wed, 11 Nov 2026 17:55:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794419732; bh=U0gyj2a8XlEB3Koh9HkxkuEE0PBRiHK2iZJInBWgPso=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=UKYp/v6NbEF370g9TA0fn7c7OJuZj8pAVbtMahBt704Jmz1loUU001Z0XJ52o4ZQv Tu+caP0u9rXrIp7PYpl9aISE3gKYs42N2uRdPGpJxjll7Dlfv31E1ywvQn+qcpMiTg H07TkeFXIyc6Gvrls2YxCxSqufUvSb+gRacz73IYPR7M1q9IM2RYHCcx5fDIabpJae ShpYetvIPQBz/IicS+0es9qoAXfOhEIJNv71uVa9qoaGx1Ct/DNhYpC+1Gv/qOEVhD HoJPZLvRGUfQBT3LXevum0Q1YPPj8NgpTUHHvvQk8gcQkaq/CDJPclv8h5IoAabJ3c urBFm58hVupqQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Henrik Enquist , Pavel Hofman , Takashi Iwai , Sasha Levin Subject: [PATCH 6.6.y 2/2] ALSA: aloop: Don't constrain playback params in notify mode Date: Wed, 11 Nov 2026 12:55:30 -0500 Message-ID: <20261111175508.3684835-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111175508.3684835-1-sashal@kernel.org> References: <20261107053132-failed-6.6-ded106036984@kernel.org> <20261111175508.3684835-1-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