usb: gadget: u_audio: Clear uac pointer when freed.

This prevents use of a stale pointer if functions are called after
g_cleanup that shouldn't be. This doesn't fix any races, but converts
a possibly silent kernel memory corruption into an obvious NULL pointer
dereference report.

Fixes: eb9fecb ("usb: gadget: f_uac2: split out audio core")
Signed-off-by: Chris Wulff <[email protected]>
Link: https://lore.kernel.org/stable/CO1PR17MB54194226DA08BFC9EBD8C163E1172%40CO1PR17MB5419.namprd17.prod.outlook.com
Link: https://lore.kernel.org/r/CO1PR17MB54194226DA08BFC9EBD8C163E1172@CO1PR17MB5419.namprd17.prod.outlook.com
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: crwulff

drivers/usb/gadget/function/u_audio.c

@@ -1420,6 +1420,8 @@ void g_audio_cleanup(struct g_audio *g_audio)
 		return;
 
 	uac = g_audio->uac;
+	g_audio->uac = NULL;
+
 	card = uac->card;
 	if (card)
 		snd_card_free_when_closed(card);