This is a note to let you know that I've just added the patch titled

ALSA: aloop: Fix racy hw constraints adjustment

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: alsa-aloop-fix-racy-hw-constraints-adjustment.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 898dfe4687f460ba337a01c11549f87269a13fa2 Mon Sep 17 00:00:00 2001

From: Takashi Iwai tiwai@suse.de Date: Thu, 4 Jan 2018 17:38:54 +0100 Subject: ALSA: aloop: Fix racy hw constraints adjustment

From: Takashi Iwai tiwai@suse.de

commit 898dfe4687f460ba337a01c11549f87269a13fa2 upstream.

The aloop driver tries to update the hw constraints of the connected target on the cable of the opened PCM substream. This is done by adding the extra hw constraints rules referring to the substream runtime->hw fields, while the other substream may update the runtime hw of another side on the fly.

This is, however, racy and may result in the inconsistent values when both PCM streams perform the prepare concurrently. One of the reason is that it overwrites the other's runtime->hw field; which is not only racy but also broken when it's called before the open of another side finishes. And, since the reference to runtime->hw isn't protected, the concurrent write may give the partial value update and become inconsistent.

This patch is an attempt to fix and clean up: - The prepare doesn't change the runtime->hw of other side any longer, but only update the cable->hw that is referred commonly. - The extra rules refer to the loopback_pcm object instead of the runtime->hw. The actual hw is deduced from cable->hw. - The extra rules take the cable_lock to protect against the race.

Fixes: b1c73fc8e697 ("ALSA: snd-aloop: Fix hw_params restrictions and checking") Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- sound/drivers/aloop.c | 51 ++++++++++++++++++++------------------------------ 1 file changed, 21 insertions(+), 30 deletions(-)

--- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -306,19 +306,6 @@ static int loopback_trigger(struct snd_p return 0; }

-static void params_change_substream(struct loopback_pcm *dpcm, - struct snd_pcm_runtime *runtime) -{ - struct snd_pcm_runtime *dst_runtime; - - if (dpcm == NULL || dpcm->substream == NULL) - return; - dst_runtime = dpcm->substream->runtime; - if (dst_runtime == NULL) - return; - dst_runtime->hw = dpcm->cable->hw; -} - static void params_change(struct snd_pcm_substream *substream) { struct snd_pcm_runtime *runtime = substream->runtime; @@ -330,10 +317,6 @@ static void params_change(struct snd_pcm cable->hw.rate_max = runtime->rate; cable->hw.channels_min = runtime->channels; cable->hw.channels_max = runtime->channels; - params_change_substream(cable->streams[SNDRV_PCM_STREAM_PLAYBACK], - runtime); - params_change_substream(cable->streams[SNDRV_PCM_STREAM_CAPTURE], - runtime); }

static int loopback_prepare(struct snd_pcm_substream *substream) @@ -621,24 +604,29 @@ static unsigned int get_cable_index(stru static int rule_format(struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule) { - - struct snd_pcm_hardware *hw = rule->private; + struct loopback_pcm *dpcm = rule->private; + struct loopback_cable *cable = dpcm->cable; struct snd_mask m;

snd_mask_none(&m); - m.bits[0] = (u_int32_t)hw->formats; - m.bits[1] = (u_int32_t)(hw->formats >> 32); + 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); return snd_mask_refine(hw_param_mask(params, rule->var), &m); }

static int rule_rate(struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule) { - struct snd_pcm_hardware *hw = rule->private; + struct loopback_pcm *dpcm = rule->private; + struct loopback_cable *cable = dpcm->cable; struct snd_interval t;

- t.min = hw->rate_min; - t.max = hw->rate_max; + mutex_lock(&dpcm->loopback->cable_lock); + t.min = cable->hw.rate_min; + t.max = cable->hw.rate_max; + mutex_unlock(&dpcm->loopback->cable_lock); t.openmin = t.openmax = 0; t.integer = 0; return snd_interval_refine(hw_param_interval(params, rule->var), &t); @@ -647,11 +635,14 @@ static int rule_rate(struct snd_pcm_hw_p static int rule_channels(struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule) { - struct snd_pcm_hardware *hw = rule->private; + struct loopback_pcm *dpcm = rule->private; + struct loopback_cable *cable = dpcm->cable; struct snd_interval t;

- t.min = hw->channels_min; - t.max = hw->channels_max; + mutex_lock(&dpcm->loopback->cable_lock); + t.min = cable->hw.channels_min; + t.max = cable->hw.channels_max; + mutex_unlock(&dpcm->loopback->cable_lock); t.openmin = t.openmax = 0; t.integer = 0; return snd_interval_refine(hw_param_interval(params, rule->var), &t); @@ -717,19 +708,19 @@ static int loopback_open(struct snd_pcm_ /* are cached -> they do not reflect the actual state */ err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, - rule_format, &runtime->hw, + rule_format, dpcm, SNDRV_PCM_HW_PARAM_FORMAT, -1); if (err < 0) goto unlock; err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE, - rule_rate, &runtime->hw, + rule_rate, dpcm, SNDRV_PCM_HW_PARAM_RATE, -1); if (err < 0) goto unlock; err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, - rule_channels, &runtime->hw, + rule_channels, dpcm, SNDRV_PCM_HW_PARAM_CHANNELS, -1); if (err < 0) goto unlock;

Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.4/alsa-pcm-remove-incorrect-snd_bug_on-usages.patch queue-4.4/alsa-aloop-fix-inconsistent-format-due-to-incomplete-rule.patch queue-4.4/alsa-pcm-add-missing-error-checks-in-oss-emulation-plugin-builder.patch queue-4.4/alsa-pcm-abort-properly-at-pending-signal-in-oss-read-write-loops.patch queue-4.4/alsa-pcm-allow-aborting-mutex-lock-at-oss-read-write-loops.patch queue-4.4/alsa-aloop-fix-racy-hw-constraints-adjustment.patch queue-4.4/alsa-aloop-release-cable-upon-open-error-path.patch