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

[Takashi Iwai]

On Thu, 27 Aug 2026 15:12:11 +0200,
Jeffin Philip wrote:
> 
> On 8/27/26 13:39, Takashi Iwai wrote:
> 
> >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.
> 
> I don't think a user can attach a device via sysfs without root permissions,
> (correct me if I am wrong).

The kcontrol can be added without root privilege.  But the
reassignment of LED-control via sysfs is only for root, so the
specific trigger pattern by syzbot is only for root.

However, in theory, it could be without root if a driver has some
built-in patterns to bind LED controls and if one would add user
elements manually later to match with it.


thanks,

Takashi