Re: [syzbot] [sound?] [usb?] general protection fault in snd_usbmidi_do_output

[Takashi Iwai]

On Sat, 27 Sep 2025 12:03:03 +0200,
syzbot wrote:
> 
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> KASAN: slab-use-after-free Write in snd_usbmidi_in_urb_complete

OK, so another fix is needed in addition.
Let's try the below.


#syz test upstream master

--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -240,6 +240,9 @@ static void snd_usbmidi_in_urb_complete(struct urb *urb)
 {
 	struct snd_usb_midi_in_endpoint *ep = urb->context;
 
+	if (ep->umidi->disconnected)
+		return;
+
 	if (urb->status == 0) {
 		dump_urb("received", urb->transfer_buffer, urb->actual_length);
 		ep->umidi->usb_protocol_ops->input(ep, urb->transfer_buffer,
@@ -275,6 +278,10 @@ static void snd_usbmidi_out_urb_complete(struct urb *urb)
 		wake_up(&ep->drain_wait);
 	}
 	spin_unlock_irqrestore(&ep->buffer_lock, flags);
+
+	if (ep->umidi->disconnected)
+		return;
+
 	if (urb->status < 0) {
 		int err = snd_usbmidi_urb_error(urb);
 		if (err < 0) {
@@ -1522,6 +1529,8 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
 {
 	int i;
 
+	timer_shutdown_sync(&umidi->error_timer);
+
 	for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
 		struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];
 		if (ep->out)
@@ -1530,7 +1539,6 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
 			snd_usbmidi_in_endpoint_delete(ep->in);
 	}
 	mutex_destroy(&umidi->mutex);
-	timer_shutdown_sync(&umidi->error_timer);
 	kfree(umidi);
 }