linux-kernel - Re: [syzbot] [sound?] [usb?] general protection fault in snd_usbmidi_do

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Message-ID: <20250923073935.7486-1-hdanton@sina.com>
Date: Tue, 23 Sep 2025 15:39:34 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+f02665daa2abeef4a947@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [sound?] [usb?] general protection fault in snd_usbmidi_do_output

> Date: Mon, 22 Sep 2025 09:54:28 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    3b08f56fbbb9 Merge tag 'x86-urgent-2025-09-20' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=176950e2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=927198eca77e75d9
> dashboard link: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14006712580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14e950e2580000

#syz test upstream master

--- x/sound/usb/midi.c
+++ y/sound/usb/midi.c
@@ -307,6 +307,8 @@ static void snd_usbmidi_do_output(struct
 	for (;;) {
 		if (!(ep->active_urbs & (1 << urb_index))) {
 			urb = ep->urbs[urb_index].urb;
+			if (!urb)
+				goto next;
 			urb->transfer_buffer_length = 0;
 			ep->umidi->usb_protocol_ops->output(ep, urb);
 			if (urb->transfer_buffer_length == 0)
@@ -319,6 +321,7 @@ static void snd_usbmidi_do_output(struct
 				break;
 			ep->active_urbs |= 1 << urb_index;
 		}
+	next:
 		if (++urb_index >= OUTPUT_URBS)
 			urb_index = 0;
 		if (urb_index == ep->next_urb)
@@ -1396,13 +1399,19 @@ static int snd_usbmidi_in_endpoint_creat
 static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
 {
 	unsigned int i;
+	unsigned long flags;
 
+	spin_lock_irqsave(&ep->buffer_lock, flags);
 	for (i = 0; i < OUTPUT_URBS; ++i)
 		if (ep->urbs[i].urb) {
-			free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
-					    ep->max_transfer);
+			struct urb *urb = ep->urbs[i].urb;
+
 			ep->urbs[i].urb = NULL;
+			spin_unlock_irqrestore(&ep->buffer_lock, flags);
+			free_urb_and_buffer(ep->umidi, urb, ep->max_transfer);
+			spin_lock_irqsave(&ep->buffer_lock, flags);
 		}
+	spin_unlock_irqrestore(&ep->buffer_lock, flags);
 }
 
 static void snd_usbmidi_out_endpoint_delete(struct snd_usb_midi_out_endpoint *ep)
@@ -1522,15 +1531,23 @@ static void snd_usbmidi_free(struct snd_
 {
 	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)
+		int j;
+
+		if (ep->out) {
+			for (j = 0; j < OUTPUT_URBS; ++j)
+				usb_kill_urb(ep->out->urbs[j].urb);
 			snd_usbmidi_out_endpoint_delete(ep->out);
-		if (ep->in)
+		}
+		if (ep->in) {
+			for (j = 0; j < INPUT_URBS; ++j)
+				usb_kill_urb(ep->in->urbs[j]);
 			snd_usbmidi_in_endpoint_delete(ep->in);
+		}
 	}
 	mutex_destroy(&umidi->mutex);
-	timer_shutdown_sync(&umidi->error_timer);
 	kfree(umidi);
 }
 
--