[PATCH 4.19 172/196] ALSA: line6: Fix racy access to midibuf

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

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

From: Takashi Iwai <tiwai@xxxxxxx>

commit 15b7a03205b31bc5623378c190d22b7ff60026f1 upstream.

There can be concurrent accesses to line6 midibuf from both the URB
completion callback and the rawmidi API access.  This could be a cause
of KMSAN warning triggered by syzkaller below (so put as reported-by
here).

This patch protects the midibuf call of the former code path with a
spinlock for avoiding the possible races.

Reported-by: syzbot+78eccfb8b3c9a85fc6c5@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/00000000000000949c061df288c5@xxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20240805130129.10872-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 sound/usb/line6/driver.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -300,12 +300,14 @@ static void line6_data_received(struct u
 {
 	struct usb_line6 *line6 = (struct usb_line6 *)urb->context;
 	struct midi_buffer *mb = &line6->line6midi->midibuf_in;
+	unsigned long flags;
 	int done;
 
 	if (urb->status == -ESHUTDOWN)
 		return;
 
 	if (line6->properties->capabilities & LINE6_CAP_CONTROL_MIDI) {
+		spin_lock_irqsave(&line6->line6midi->lock, flags);
 		done =
 			line6_midibuf_write(mb, urb->transfer_buffer, urb->actual_length);
 
@@ -314,12 +316,15 @@ static void line6_data_received(struct u
 			dev_dbg(line6->ifcdev, "%d %d buffer overflow - message skipped\n",
 				done, urb->actual_length);
 		}
+		spin_unlock_irqrestore(&line6->line6midi->lock, flags);
 
 		for (;;) {
+			spin_lock_irqsave(&line6->line6midi->lock, flags);
 			done =
 				line6_midibuf_read(mb, line6->buffer_message,
 						   LINE6_MIDI_MESSAGE_MAXLEN,
 						   LINE6_MIDIBUF_READ_RX);
+			spin_unlock_irqrestore(&line6->line6midi->lock, flags);
 
 			if (done <= 0)
 				break;






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