[alsa-devel] [PATCH] ALSA: firewire-lib: avoid NULL pointer dereference after closing MIDI port

[Takashi Sakamoto]

When asynchronous MIDI port is closed before callbacked, the callback
function causes NULL pointer dereference to missing MIDI substream.

This commit fixes this bug.

Fixes: e8a40d9bcb23('ALSA: firewire-lib: schedule work again when MIDI substream has rest of MIDI messages')
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/firewire/lib.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sound/firewire/lib.c b/sound/firewire/lib.c
index edf1c8b..f80aafa 100644
--- a/sound/firewire/lib.c
+++ b/sound/firewire/lib.c
@@ -74,7 +74,11 @@ static void async_midi_port_callback(struct fw_card *card, int rcode,
 	struct snd_fw_async_midi_port *port = callback_data;
 	struct snd_rawmidi_substream *substream = ACCESS_ONCE(port->substream);
 
-	if (rcode == RCODE_COMPLETE && substream != NULL)
+	/* This port is closed. */
+	if (substream == NULL)
+		return;
+
+	if (rcode == RCODE_COMPLETE)
 		snd_rawmidi_transmit_ack(substream, port->consume_bytes);
 	else if (!rcode_is_permanent_error(rcode))
 		/* To start next transaction immediately for recovery. */
-- 
2.1.4