6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Junrui Luo <redacted>

[ Upstream commit e11c5c13ce0ab2325d38fe63500be1dd88b81e38 ]

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

Reported-by: Yuhao Jiang <redacted>
Reported-by: Junrui Luo <redacted>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <redacted>
Link: https://patch.msgid.link/SYBPR01MB7881DF762CAB45EE42F6D812AFC2A@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Takashi Iwai <redacted>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/isa/wavefront/wavefront_midi.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/sound/isa/wavefront/wavefront_midi.c
+++ b/sound/isa/wavefront/wavefront_midi.c

@@ -278,6 +278,7 @@ static int snd_wavefront_midi_input_clos
 	        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_clo
 	        return -EIO;
 
 	guard(spinlock_irqsave)(&midi->open);
+	midi->substream_output[mpu] = NULL;
 	midi->mode[mpu] &= ~MPU401_MODE_OUTPUT;
 	return 0;
 }