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=1794591608; b=Jt9Y8FGXcwthn+IqiXsqWKps+UdIbkTAvyvpYydUpNLK0f9zslG8dooWRWAuRmL8h6++ PRqYQVvH59fNRwVC5qTyfZs6OXdiDXyiF7eQQY+egwhI/pGzNTZr6i3Di0tMQl0l9yBlR 8/NqE0iRGYBz1ZcqGiahUsTDVOOu5k0MU+CC+/Asi3C0r2KcfyXjZ6M1AfcewaxWZ/qAm YkntqKQKMehEodD4ZBaSlkBEuhMP7CzcInLG9H7n1GjJ6ygXtUmxhUhL+MhZOLp4oD+Wl pe/cCY637e69mjKvUOqBOjyh72Ep71StpsRUnwEaqhz/oHuq9F1SNmCvhju/Yy0AFyQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794591608; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=5kh/mSLuqrnOc1pVrPSLCMUmgYxvkse2A73SJ4xPvU4=; b=BghPqpcNDtXC7AcE5i7qHXfODfUKPwk3SgY1f5SfUvnJ8gYS2mzjoeIySlqn00Z5Vq1G yiu2jvMmE0vHufoi/2jRJUKQE8KjvBtaYeWmSBNkxB9KXlNfE+/BOfPdJ8W08gvjrXTdd 5/nkZlCsJakrGjXqtf9vf9LmzLexJvunDqBXVx6TazfouFP+2r1HKmdRNk7kJpY9b6htL 74mrWYiirlYW8xn/rjiE9dAzRjmV7T+lVSoyGSEdaQZPUETP3I41bBF3oOqRhzM8ub1pn axLCWbvZRsoYFWuZrp1ZzA4A7lD/lPQYxTVaCRakG6/3abDNtReDiUJtjWcXn8/WyOA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=qJwVA84m; 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 3582A606B45B; Fri, 13 Nov 2026 17:40:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=qJwVA84m Received: by smtp.kernel.org (Postfix) with ESMTPSA id D54461F000C8; Fri, 13 Nov 2026 17:40:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794591608; bh=5kh/mSLuqrnOc1pVrPSLCMUmgYxvkse2A73SJ4xPvU4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=qJwVA84mLaRBBrje7ILX3ekrIQilOQ6YW/ohfFOcl44yWBtXQkqasV4H/nKpFtbsV QICHN6jokfM+TvQasIemLSLo3HWv03f4DfpSoRb+v+E0NWj25NXoKjqCzhMDdF6KPr 0stfKWAAgQdnKr23UYm4FyITVVxqK8noGOt7lSn4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Pavel Hofman , Henrik Enquist , Takashi Iwai , Sasha Levin Subject: [PATCH 6.12 648/670] ALSA: aloop: Dont constrain playback params in notify mode Date: Fri, 13 Nov 2026 10:53:32 -0500 Message-ID: <20261113153833.779005171@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ 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