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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.de>,
        Ovidiu Panait <ovidiu.panait@windriver.com>
Subject: [PATCH 4.14 11/14] ALSA: pcm: Fix races among concurrent prepare and hw_params/hw_free calls
Date:   Fri, 13 May 2022 16:23:27 +0200
Message-Id: <20220513142227.717010807@linuxfoundation.org>
In-Reply-To: <20220513142227.381154244@linuxfoundation.org>
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From: Takashi Iwai <tiwai@suse.de>

commit 3c3201f8c7bb77eb53b08a3ca8d9a4ddc500b4c0 upstream.

Like the previous fixes to hw_params and hw_free ioctl races, we need
to paper over the concurrent prepare ioctl calls against hw_params and
hw_free, too.

This patch implements the locking with the existing
runtime->buffer_mutex for prepare ioctls.  Unlike the previous case
for snd_pcm_hw_hw_params() and snd_pcm_hw_free(), snd_pcm_prepare() is
performed to the linked streams, hence the lock can't be applied
simply on the top.  For tracking the lock in each linked substream, we
modify snd_pcm_action_group() slightly and apply the buffer_mutex for
the case stream_lock=false (formerly there was no lock applied)
there.

Cc: <stable@vger.kernel.org>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220322170720.3529-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[OP: backport to 4.14: adjusted context]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/core/pcm_native.c |   32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1046,15 +1046,17 @@ struct action_ops {
  */
 static int snd_pcm_action_group(const struct action_ops *ops,
 				struct snd_pcm_substream *substream,
-				int state, int do_lock)
+				int state, int stream_lock)
 {
 	struct snd_pcm_substream *s = NULL;
 	struct snd_pcm_substream *s1;
 	int res = 0, depth = 1;
 
 	snd_pcm_group_for_each_entry(s, substream) {
-		if (do_lock && s != substream) {
-			if (s->pcm->nonatomic)
+		if (s != substream) {
+			if (!stream_lock)
+				mutex_lock_nested(&s->runtime->buffer_mutex, depth);
+			else if (s->pcm->nonatomic)
 				mutex_lock_nested(&s->self_group.mutex, depth);
 			else
 				spin_lock_nested(&s->self_group.lock, depth);
@@ -1082,18 +1084,18 @@ static int snd_pcm_action_group(const st
 		ops->post_action(s, state);
 	}
  _unlock:
-	if (do_lock) {
-		/* unlock streams */
-		snd_pcm_group_for_each_entry(s1, substream) {
-			if (s1 != substream) {
-				if (s1->pcm->nonatomic)
-					mutex_unlock(&s1->self_group.mutex);
-				else
-					spin_unlock(&s1->self_group.lock);
-			}
-			if (s1 == s)	/* end */
-				break;
+	/* unlock streams */
+	snd_pcm_group_for_each_entry(s1, substream) {
+		if (s1 != substream) {
+			if (!stream_lock)
+				mutex_unlock(&s1->runtime->buffer_mutex);
+			else if (s1->pcm->nonatomic)
+				mutex_unlock(&s1->self_group.mutex);
+			else
+				spin_unlock(&s1->self_group.lock);
 		}
+		if (s1 == s)	/* end */
+			break;
 	}
 	return res;
 }
@@ -1174,10 +1176,12 @@ static int snd_pcm_action_nonatomic(cons
 	int res;
 
 	down_read(&snd_pcm_link_rwsem);
+	mutex_lock(&substream->runtime->buffer_mutex);
 	if (snd_pcm_stream_linked(substream))
 		res = snd_pcm_action_group(ops, substream, state, 0);
 	else
 		res = snd_pcm_action_single(ops, substream, state);
+	mutex_unlock(&substream->runtime->buffer_mutex);
 	up_read(&snd_pcm_link_rwsem);
 	return res;
 }