[PATCH] usb: gadget: f_uac1_legacy: cancel playback_work before freeing f_audio

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

The OUT endpoint completion (f_audio_out_ep_complete) and the set_alt path
schedule audio->playback_work, whose handler (f_audio_playback_work)
dereferences the f_audio (audio->lock, audio->play_queue, audio->card).
On teardown f_audio_free() frees the f_audio with kfree(audio) but never
cancels playback_work -- f_audio_disable() is empty and nothing else
drains it. A playback_work still pending when the function is freed runs
against freed memory, a use-after-free.

Cancel playback_work in f_audio_free() before kfree(audio). By then the
function is unbound and the OUT endpoint is disabled, so the work cannot
be re-queued and cancel_work_sync() is sufficient.

This was reproduced with KASAN as a slab-use-after-free in
u_audio_playback(), reached from f_audio_playback_work(), under dummy_hcd:
with a UAC1 playback stream active, unlinking the configfs function frees
the f_audio in f_audio_free() while the work is still in flight. A delay
was added to the gadget streaming path to make the schedule-vs-free race
land deterministically; the missing cancel is present regardless. With
this patch applied the splat no longer occurs.

Fixes: d355339eecd9 ("usb: gadget: function: make current f_uac1 implementation legacy")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
 drivers/usb/gadget/function/f_uac1_legacy.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/gadget/function/f_uac1_legacy.c b/drivers/usb/gadget/function/f_uac1_legacy.c
index 7c8d60c..2dca5cd 100644
--- a/drivers/usb/gadget/function/f_uac1_legacy.c
+++ b/drivers/usb/gadget/function/f_uac1_legacy.c
@@ -945,6 +945,12 @@ static void f_audio_free(struct usb_function *f)
 
 	gaudio_cleanup(&audio->card);
 	opts = container_of(f->fi, struct f_uac1_legacy_opts, func_inst);
+	/*
+	 * The function is already unbound, so the OUT endpoint can no longer
+	 * queue playback_work. Drain any work still pending before the
+	 * containing f_audio is freed, otherwise it runs against freed memory.
+	 */
+	cancel_work_sync(&audio->playback_work);
 	kfree(audio);
 	mutex_lock(&opts->lock);
 	--opts->refcnt;
-- 
2.43.0