github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

ALSA: aloop: Don't constrain playback params in notify mode

Browse Source 
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 898dfe4687 ("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
826af7fa62 ("ALSA: aloop: Fix racy access at PCM trigger") and
commit e5c33cdc6f ("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: 898dfe4687 ("ALSA: aloop: Fix racy hw constraints adjustment")
Reported-by: Pavel Hofman <pavel.hofman@ivitera.com>
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 <henrik.enquist@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20261003-aloop-notify-fix-v1-1-ba5dfb831bf5@gmail.com
This commit is contained in:
Henrik Enquist 2026-10-03 15:26:11 +02:00 committed by Takashi Iwai
parent af53cdc10c
commit ded1060369
1 changed files with 20 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
sound/drivers/aloop.c
View File

@ -1073,6 +1073,18 @@ 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)
{
@ -1082,6 +1094,8 @@ 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);
}
@ -1096,6 +1110,8 @@ 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;
}
@ -1112,6 +1128,8 @@ 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;
}
@ -1128,6 +1146,8 @@ 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;
}