[PATCH] ALSA: firewire-motu: Protect register DSP event queue positions

[Cássio Gabriel]

The register DSP event queue is updated under parser->lock, but
snd_motu_register_dsp_message_parser_count_event() reads pull_pos and
push_pos without the lock.
snd_motu_register_dsp_message_parser_copy_event() also reads both queue
positions before taking the lock.

Protect these accesses with parser->lock as well. This keeps the hwdep
poll/read path consistent with the producer side and with the cached
meter/parameter accessors.

Fixes: 634ec0b2906e ("ALSA: firewire-motu: notify event for parameter change in register DSP model")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>
---
 sound/firewire/motu/motu-register-dsp-message-parser.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/sound/firewire/motu/motu-register-dsp-message-parser.c b/sound/firewire/motu/motu-register-dsp-message-parser.c
index a8053e3ef065..4ec23e6880d9 100644
--- a/sound/firewire/motu/motu-register-dsp-message-parser.c
+++ b/sound/firewire/motu/motu-register-dsp-message-parser.c
@@ -386,6 +386,8 @@ unsigned int snd_motu_register_dsp_message_parser_count_event(struct snd_motu *m
 {
 	struct msg_parser *parser = motu->message_parser;
 
+	guard(spinlock_irqsave)(&parser->lock);
+
 	if (parser->pull_pos > parser->push_pos)
 		return EVENT_QUEUE_SIZE - parser->pull_pos + parser->push_pos;
 	else
@@ -395,13 +397,14 @@ unsigned int snd_motu_register_dsp_message_parser_count_event(struct snd_motu *m
 bool snd_motu_register_dsp_message_parser_copy_event(struct snd_motu *motu, u32 *event)
 {
 	struct msg_parser *parser = motu->message_parser;
-	unsigned int pos = parser->pull_pos;
-
-	if (pos == parser->push_pos)
-		return false;
+	unsigned int pos;
 
 	guard(spinlock_irqsave)(&parser->lock);
 
+	if (parser->pull_pos == parser->push_pos)
+		return false;
+
+	pos = parser->pull_pos;
 	*event = parser->event_queue[pos];
 
 	++pos;

---
base-commit: 38c607c673155d6335591cdbd9c785fb2b7550e5
change-id: 20260501-alsa-firewire-motu-event-locking-d159b967a62c

Best regards,
--  
Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>