ALSA: firewire-lib: avoid NULL pointer dereference after closing MIDI port

[firefly-linux-kernel-4.4.55.git] / sound / firewire / lib.c

diff --git a/sound/firewire/lib.c b/sound/firewire/lib.c
index edf1c8bd25a6600b67c3a3f3d697b3c1efb6c741..f80aafa44c89499ff92b0b3af0bc761ca49c0567 100644 (file)
--- 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. */