Commit 0718a78f authored May 19, 2025 by Takashi Iwai

ALSA: usb-audio: Kill timer properly at removal



The USB-audio MIDI code initializes the timer, but in a rare case, the
driver might be freed without the disconnect call.  This leaves the
timer in an active state while the assigned object is released via
snd_usbmidi_free(), which ends up with a kernel warning when the debug
configuration is enabled, as spotted by fuzzer.

For avoiding the problem, put timer_shutdown_sync() at
snd_usbmidi_free(), so that the timer can be killed properly.
While we're at it, replace the existing timer_delete_sync() at the
disconnect callback with timer_shutdown_sync(), too.

Reported-by:  <syzbot+d8f72178ab6783a7daea@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/681c70d7.050a0220.a19a9.00c6.GAE@google.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20250519212031.14436-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent ff05770d

sound/usb/midi.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -1530,6 +1530,7 @@ 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);
		}

		@@ -1553,7 +1554,7 @@ void snd_usbmidi_disconnect(struct list_head *p)
		spin_unlock_irq(&umidi->disc_lock);
		up_write(&umidi->disc_rwsem);

		timer_delete_sync(&umidi->error_timer);
		timer_shutdown_sync(&umidi->error_timer);

		for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
		struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];