ALSA: control: Don't add invalid kcontrols to LED layer

ALSA: control: Don't add invalid kcontrols to LED layer

[ Upstream commit 74e3b979ce8b78a690f8b94ccf2e2c965f7f5c11 ]

The kcontrol LED state layer tries to track the all associated
kcontrol elements with naive assumptions that they are readable.
But one can create a write-only element that has no get callback (even
a user element can do it), and this may lead to a NULL dereference at
the call chain of snd_ctl_led_notify(), as found by syzkaller.

For avoiding the Oops, add a sanity check of the kcontrol's info and
get callbacks, and just skip the invalid kcontrols before assigning
the kctl to the LED layer.

Reported-by: syzbot+b7fe2760ea6f1ee44b4d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/6a9007b3.1d9ded08.62e62.00cd.GAE@google.com
Fixes: 22d8de62f11b ("ALSA: control - add generic LED trigger module as the new control layer")
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20260827113951.893291-1-tiwai@suse.de
Signed-off-by: Sasha Levin <sashal@kernel.org>