[alsa-devel] [PATCH 0/3] ALSA: KCSAN fixes

[alsa-devel] [PATCH 0/3] ALSA: KCSAN fixes

[Takashi Iwai]

Hi,

recently syzbot reports repeatedly about the concurrent accesses with
KCSAN.  Those should be mostly harmless but still safer to be papered
over, so here are fixes.

There are two fixes for ALSA sequencer core, one about applying the
spinlock for the queue bitmap flag accesses, and another about the
current time retrievals.  The last patch is about rawmidi and changes
simply bit fields to bools.

I didn't mark them Cc-to-stable because there are no reproducer and
the patterns are basically safe -- although it's fine to backport
these patches to stable branches.


Takashi

===

Takashi Iwai (3):
  ALSA: seq: Avoid concurrent access to queue flags
  ALSA: seq: Fix concurrent access to queue current tick/time
  ALSA: rawmidi: Avoid bit fields for state flags

 include/sound/rawmidi.h        |  6 +++---
 sound/core/seq/seq_clientmgr.c |  4 ++--
 sound/core/seq/seq_queue.c     | 29 ++++++++++++++++++++++-------
 sound/core/seq/seq_timer.c     | 13 ++++++++++---
 sound/core/seq/seq_timer.h     |  3 ++-
 5 files changed, 39 insertions(+), 16 deletions(-)

-- 
2.16.4

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[alsa-devel] [PATCH 1/3] ALSA: seq: Avoid concurrent access to queue flags

[Takashi Iwai]

The queue flags are represented in bit fields and the concurrent
access may result in unexpected results.  Although the current code
should be mostly OK as it's only reading a field while writing other
fields as KCSAN reported, it's safer to cover both with a proper
spinlock protection.

This patch fixes the possible concurrent read by protecting with
q->owner_lock.  Also the queue owner field is protected as well since
it's the field to be protected by the lock itself.

Reported-by: syzbot+65c6c92d04304d0a8efc@syzkaller.appspotmail.com
Reported-by: syzbot+e60ddfa48717579799dd@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/seq/seq_queue.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
index caf68bf42f13..20c552cf8398 100644
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -392,6 +392,7 @@ int snd_seq_queue_check_access(int queueid, int client)
 int snd_seq_queue_set_owner(int queueid, int client, int locked)
 {
 	struct snd_seq_queue *q = queueptr(queueid);
+	unsigned long flags;
 
 	if (q == NULL)
 		return -EINVAL;
@@ -401,8 +402,10 @@ int snd_seq_queue_set_owner(int queueid, int client, int locked)
 		return -EPERM;
 	}
 
+	spin_lock_irqsave(&q->owner_lock, flags);
 	q->locked = locked ? 1 : 0;
 	q->owner = client;
+	spin_unlock_irqrestore(&q->owner_lock, flags);
 	queue_access_unlock(q);
 	queuefree(q);
 
@@ -539,15 +542,17 @@ void snd_seq_queue_client_termination(int client)
 	unsigned long flags;
 	int i;
 	struct snd_seq_queue *q;
+	bool matched;
 
 	for (i = 0; i < SNDRV_SEQ_MAX_QUEUES; i++) {
 		if ((q = queueptr(i)) == NULL)
 			continue;
 		spin_lock_irqsave(&q->owner_lock, flags);
-		if (q->owner == client)
+		matched = (q->owner == client);
+		if (matched)
 			q->klocked = 1;
 		spin_unlock_irqrestore(&q->owner_lock, flags);
-		if (q->owner == client) {
+		if (matched) {
 			if (q->timer->running)
 				snd_seq_timer_stop(q->timer);
 			snd_seq_timer_reset(q->timer);
@@ -739,6 +744,8 @@ void snd_seq_info_queues_read(struct snd_info_entry *entry,
 	int i, bpm;
 	struct snd_seq_queue *q;
 	struct snd_seq_timer *tmr;
+	bool locked;
+	int owner;
 
 	for (i = 0; i < SNDRV_SEQ_MAX_QUEUES; i++) {
 		if ((q = queueptr(i)) == NULL)
@@ -750,9 +757,14 @@ void snd_seq_info_queues_read(struct snd_info_entry *entry,
 		else
 			bpm = 0;
 
+		spin_lock_irq(&q->owner_lock);
+		locked = q->locked;
+		owner = q->owner;
+		spin_unlock_irq(&q->owner_lock);
+
 		snd_iprintf(buffer, "queue %d: [%s]\n", q->queue, q->name);
-		snd_iprintf(buffer, "owned by client    : %d\n", q->owner);
-		snd_iprintf(buffer, "lock status        : %s\n", q->locked ? "Locked" : "Free");
+		snd_iprintf(buffer, "owned by client    : %d\n", owner);
+		snd_iprintf(buffer, "lock status        : %s\n", locked ? "Locked" : "Free");
 		snd_iprintf(buffer, "queued time events : %d\n", snd_seq_prioq_avail(q->timeq));
 		snd_iprintf(buffer, "queued tick events : %d\n", snd_seq_prioq_avail(q->tickq));
 		snd_iprintf(buffer, "timer state        : %s\n", tmr->running ? "Running" : "Stopped");
-- 
2.16.4

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[alsa-devel] [PATCH 2/3] ALSA: seq: Fix concurrent access to queue current tick/time

[Takashi Iwai]

snd_seq_check_queue() passes the current tick and time of the given
queue as a pointer to snd_seq_prioq_cell_out(), but those might be
updated concurrently by the seq timer update.

Fix it by retrieving the current tick and time via the proper helper
functions at first, and pass those values to snd_seq_prioq_cell_out()
later in the loops.

snd_seq_timer_get_cur_time() takes a new argument and adjusts with the
current system time only when it's requested so; this update isn't
needed for snd_seq_check_queue(), as it's called either from the
interrupt handler or right after queuing.

Also, snd_seq_timer_get_cur_tick() is changed to read the value in the
spinlock for the concurrency, too.

Reported-by: syzbot+fd5e0eaa1a32999173b2@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/seq/seq_clientmgr.c |  4 ++--
 sound/core/seq/seq_queue.c     |  9 ++++++---
 sound/core/seq/seq_timer.c     | 13 ++++++++++---
 sound/core/seq/seq_timer.h     |  3 ++-
 4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 6d9592f0ae1d..cc93157fa950 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -580,7 +580,7 @@ static int update_timestamp_of_queue(struct snd_seq_event *event,
 	event->queue = queue;
 	event->flags &= ~SNDRV_SEQ_TIME_STAMP_MASK;
 	if (real_time) {
-		event->time.time = snd_seq_timer_get_cur_time(q->timer);
+		event->time.time = snd_seq_timer_get_cur_time(q->timer, true);
 		event->flags |= SNDRV_SEQ_TIME_STAMP_REAL;
 	} else {
 		event->time.tick = snd_seq_timer_get_cur_tick(q->timer);
@@ -1659,7 +1659,7 @@ static int snd_seq_ioctl_get_queue_status(struct snd_seq_client *client,
 	tmr = queue->timer;
 	status->events = queue->tickq->cells + queue->timeq->cells;
 
-	status->time = snd_seq_timer_get_cur_time(tmr);
+	status->time = snd_seq_timer_get_cur_time(tmr, true);
 	status->tick = snd_seq_timer_get_cur_tick(tmr);
 
 	status->running = tmr->running;
diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
index 20c552cf8398..71a6ea62c3be 100644
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -238,6 +238,8 @@ void snd_seq_check_queue(struct snd_seq_queue *q, int atomic, int hop)
 {
 	unsigned long flags;
 	struct snd_seq_event_cell *cell;
+	snd_seq_tick_time_t cur_tick;
+	snd_seq_real_time_t cur_time;
 
 	if (q == NULL)
 		return;
@@ -254,17 +256,18 @@ void snd_seq_check_queue(struct snd_seq_queue *q, int atomic, int hop)
 
       __again:
 	/* Process tick queue... */
+	cur_tick = snd_seq_timer_get_cur_tick(q->timer);
 	for (;;) {
-		cell = snd_seq_prioq_cell_out(q->tickq,
-					      &q->timer->tick.cur_tick);
+		cell = snd_seq_prioq_cell_out(q->tickq, &cur_tick);
 		if (!cell)
 			break;
 		snd_seq_dispatch_event(cell, atomic, hop);
 	}
 
 	/* Process time queue... */
+	cur_time = snd_seq_timer_get_cur_time(q->timer, false);
 	for (;;) {
-		cell = snd_seq_prioq_cell_out(q->timeq, &q->timer->cur_time);
+		cell = snd_seq_prioq_cell_out(q->timeq, &cur_time);
 		if (!cell)
 			break;
 		snd_seq_dispatch_event(cell, atomic, hop);
diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index be59b59c9be4..1645e4142e30 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -428,14 +428,15 @@ int snd_seq_timer_continue(struct snd_seq_timer *tmr)
 }
 
 /* return current 'real' time. use timeofday() to get better granularity. */
-snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr)
+snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr,
+					       bool adjust_ktime)
 {
 	snd_seq_real_time_t cur_time;
 	unsigned long flags;
 
 	spin_lock_irqsave(&tmr->lock, flags);
 	cur_time = tmr->cur_time;
-	if (tmr->running) { 
+	if (adjust_ktime && tmr->running) {
 		struct timespec64 tm;
 
 		ktime_get_ts64(&tm);
@@ -452,7 +453,13 @@ snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr)
  high PPQ values) */
 snd_seq_tick_time_t snd_seq_timer_get_cur_tick(struct snd_seq_timer *tmr)
 {
-	return tmr->tick.cur_tick;
+	snd_seq_tick_time_t cur_tick;
+	unsigned long flags;
+
+	spin_lock_irqsave(&tmr->lock, flags);
+	cur_tick = tmr->tick.cur_tick;
+	spin_unlock_irqrestore(&tmr->lock, flags);
+	return cur_tick;
 }
 
 
diff --git a/sound/core/seq/seq_timer.h b/sound/core/seq/seq_timer.h
index 66c3e344eae3..4bec57df8158 100644
--- a/sound/core/seq/seq_timer.h
+++ b/sound/core/seq/seq_timer.h
@@ -120,7 +120,8 @@ int snd_seq_timer_set_tempo_ppq(struct snd_seq_timer *tmr, int tempo, int ppq);
 int snd_seq_timer_set_position_tick(struct snd_seq_timer *tmr, snd_seq_tick_time_t position);
 int snd_seq_timer_set_position_time(struct snd_seq_timer *tmr, snd_seq_real_time_t position);
 int snd_seq_timer_set_skew(struct snd_seq_timer *tmr, unsigned int skew, unsigned int base);
-snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr);
+snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr,
+					       bool adjust_ktime);
 snd_seq_tick_time_t snd_seq_timer_get_cur_tick(struct snd_seq_timer *tmr);
 
 extern int seq_default_timer_class;
-- 
2.16.4

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[alsa-devel] [PATCH 3/3] ALSA: rawmidi: Avoid bit fields for state flags

[Takashi Iwai]

The rawmidi state flags (opened, append, active_sensing) are stored in
bit fields that can be potentially racy when concurrently accessed
without any locks.  Although the current code should be fine, there is
also no any real benefit by keeping the bitfields for this kind of
short number of members.

This patch changes those bit fields flags to the simple bool fields.
There should be no size increase of the snd_rawmidi_substream by this
change.

Reported-by: syzbot+576cc007eb9f2c968200@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 include/sound/rawmidi.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h
index 40ab20439fee..a36b7227a15a 100644
--- a/include/sound/rawmidi.h
+++ b/include/sound/rawmidi.h
@@ -77,9 +77,9 @@ struct snd_rawmidi_substream {
 	struct list_head list;		/* list of all substream for given stream */
 	int stream;			/* direction */
 	int number;			/* substream number */
-	unsigned int opened: 1,		/* open flag */
-		     append: 1,		/* append flag (merge more streams) */
-		     active_sensing: 1; /* send active sensing when close */
+	bool opened;			/* open flag */
+	bool append;			/* append flag (merge more streams) */
+	bool active_sensing;		/* send active sensing when close */
 	int use_count;			/* use counter (for output) */
 	size_t bytes;
 	struct snd_rawmidi *rmidi;
-- 
2.16.4

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