ALSA: wavefront: Clear substream pointers on close

commit e11c5c1 upstream.

Clear substream pointers in close functions to avoid leaving dangling
pointers, helping to improve code safety and
prevents potential issues.

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reported-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB7881DF762CAB45EE42F6D812AFC2A@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: avasummer

sound/isa/wavefront/wavefront_midi.c

@@ -278,6 +278,7 @@ static int snd_wavefront_midi_input_close(struct snd_rawmidi_substream *substrea
 	        return -EIO;
 
 	guard(spinlock_irqsave)(&midi->open);
+	midi->substream_input[mpu] = NULL;
 	midi->mode[mpu] &= ~MPU401_MODE_INPUT;
 
 	return 0;
@@ -300,6 +301,7 @@ static int snd_wavefront_midi_output_close(struct snd_rawmidi_substream *substre
 	        return -EIO;
 
 	guard(spinlock_irqsave)(&midi->open);
+	midi->substream_output[mpu] = NULL;
 	midi->mode[mpu] &= ~MPU401_MODE_OUTPUT;
 	return 0;
 }