[PATCH] usb: gadget: u_audio: reject srate request for unconfigured direction

u_audio_get_playback_srate() unconditionally locks and reads
uac->p_prm.lock/srate, but g_audio_setup() only initializes
p_prm.lock when p_chmask is set. On a UAC2 instance configured
without a playback direction, this results in acquiring a
never spin_lock_init()'d lock when a GET_CUR sample rate
request targets playback, triggering a lockdep "trying to
register non-static key" warning.

Reject the request with -EOPNOTSUPP when p_chmask is not set,
before touching prm->lock.

Fixes: eb3a1ce6f5ed ("usb: gadget: u_audio: Add capture/playback srate getter")
Reported-by: syzbot+e1d0e66badecc32d45eb@syzkaller.appspotmail.com
Closes: http://syzkaller.appspot.com/bug?extid=e1d0e66badecc32d45eb
Signed-off-by: Deepanshu Kartikey <redacted>
---
 drivers/usb/gadget/function/u_audio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index e53f2927b539..ff811ea1e25a 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c

@@ -575,6 +575,9 @@ int u_audio_get_playback_srate(struct g_audio *audio_dev, u32 *val)
 	struct uac_rtd_params *prm;
 	unsigned long flags;
 
+	if (!audio_dev->params.p_chmask)
+		return -EOPNOTSUPP;
+
 	prm = &uac->p_prm;
 	spin_lock_irqsave(&prm->lock, flags);
 	*val = prm->srate;

-- 
2.43.0