sound: snd_ctl_remove_user_ctl: prevent removal of kernel controls

Ensure that userspace can remove only user controls.  Controls created
by kernel drivers must not be removed because they might be referenced
in calls to snd_ctl_notify().

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/control.c b/sound/core/control.c
index bc64b723415b9e7fc9198db049e422a085807126..a8b7fabe645ef1d0bf7fc82f4d15e4cd7024b1ed 100644 (file)
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -436,6 +436,10 @@ static int snd_ctl_remove_user_ctl(struct snd_ctl_file * file,
                ret = -ENOENT;
                goto error;
        }
+       if (!(kctl->vd[0].access & SNDRV_CTL_ELEM_ACCESS_USER)) {
+               ret = -EINVAL;
+               goto error;
+       }
        for (idx = 0; idx < kctl->count; idx++)
                if (kctl->vd[idx].owner != NULL && kctl->vd[idx].owner != file) {
                        ret = -EBUSY;