[PATCH] ALSA: hda: Fix UAF of leds class devs at unbinding

[Takashi Iwai]

The LED class devices that are created by HD-audio codec drivers are
registered via devm_led_classdev_register() and associated with the
HD-audio codec device.  Unfortunately, it turned out that the devres
release doesn't work for this case; namely, since the codec resource
release happens before the devm call chain, it triggers a NULL
dereference or a UAF for a stale set_brightness_delay callback.

For fixing the bug, this patch changes the LED class device register
and unregister in a manual manner without devres, keeping the
instances in hda_gen_spec.

Reported-by: Alexander Sergeyev <sergeev917 at gmail.com>
Cc: <stable at vger.kernel.org>
Link: https://lore.kernel.org/r/20220111195229.a77wrpjclqwrx4bx@localhost.localdomain
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/pci/hda/hda_generic.c | 17 +++++++++++++++--
 sound/pci/hda/hda_generic.h |  3 +++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/sound/pci/hda/hda_generic.c b/sound/pci/hda/hda_generic.c
index 3bf5e3410703..fc114e522480 100644
--- a/sound/pci/hda/hda_generic.c
+++ b/sound/pci/hda/hda_generic.c
@@ -91,6 +91,12 @@ static void snd_hda_gen_spec_free(struct hda_gen_spec *spec)
 	free_kctls(spec);
 	snd_array_free(&spec->paths);
 	snd_array_free(&spec->loopback_list);
+#ifdef CONFIG_SND_HDA_GENERIC_LEDS
+	if (spec->led_cdevs[LED_AUDIO_MUTE])
+		led_classdev_unregister(spec->led_cdevs[LED_AUDIO_MUTE]);
+	if (spec->led_cdevs[LED_AUDIO_MICMUTE])
+		led_classdev_unregister(spec->led_cdevs[LED_AUDIO_MICMUTE]);
+#endif
 }
 
 /*
@@ -3922,7 +3928,10 @@ static int create_mute_led_cdev(struct hda_codec *codec,
 						enum led_brightness),
 				bool micmute)
 {
+	struct hda_gen_spec *spec = codec->spec;
 	struct led_classdev *cdev;
+	int idx = micmute ? LED_AUDIO_MICMUTE : LED_AUDIO_MUTE;
+	int err;
 
 	cdev = devm_kzalloc(&codec->core.dev, sizeof(*cdev), GFP_KERNEL);
 	if (!cdev)
@@ -3932,10 +3941,14 @@ static int create_mute_led_cdev(struct hda_codec *codec,
 	cdev->max_brightness = 1;
 	cdev->default_trigger = micmute ? "audio-micmute" : "audio-mute";
 	cdev->brightness_set_blocking = callback;
-	cdev->brightness = ledtrig_audio_get(micmute ? LED_AUDIO_MICMUTE : LED_AUDIO_MUTE);
+	cdev->brightness = ledtrig_audio_get(idx);
 	cdev->flags = LED_CORE_SUSPENDRESUME;
 
-	return devm_led_classdev_register(&codec->core.dev, cdev);
+	err = led_classdev_register(&codec->core.dev, cdev);
+	if (err < 0)
+		return err;
+	spec->led_cdevs[idx] = cdev;
+	return 0;
 }
 
 /**
diff --git a/sound/pci/hda/hda_generic.h b/sound/pci/hda/hda_generic.h
index 8e1bc8ea74fc..34eba40cc6e6 100644
--- a/sound/pci/hda/hda_generic.h
+++ b/sound/pci/hda/hda_generic.h
@@ -294,6 +294,9 @@ struct hda_gen_spec {
 				   struct hda_jack_callback *cb);
 	void (*mic_autoswitch_hook)(struct hda_codec *codec,
 				    struct hda_jack_callback *cb);
+
+	/* leds */
+	struct led_classdev *led_cdevs[NUM_AUDIO_LEDS];
 };
 
 /* values for add_stereo_mix_input flag */
-- 
2.31.1