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

[Takashi Iwai <tiwai@suse.de>]

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")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/control_led.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/core/control_led.c b/sound/core/control_led.c
index 8cbacee57ce7..3d13bbec1c54 100644
--- a/sound/core/control_led.c
+++ b/sound/core/control_led.c
@@ -255,6 +255,8 @@ static int snd_ctl_led_set_id(int card_number, struct snd_ctl_elem_id *id,
 	kctl = snd_ctl_find_id(card, id);
 	if (!kctl)
 		return -ENOENT;
+	if (!kctl->info || !kctl->get)
+		return -EINVAL;
 	ioff = snd_ctl_get_ioff(kctl, id);
 	vd = &kctl->vd[ioff];
 	access = vd->access & SNDRV_CTL_ELEM_ACCESS_LED_MASK;
-- 
2.55.0