[PATCH 4.19 051/131] ALSA: usb-audio: Fix OOB access of mixer element list

Sasha Levin
2020-06-29T20:03:29Z

From: Takashi Iwai <tiwai@suse.de>

commit 220345e98f1cdc768eeb6e3364a0fa7ab9647fe7 upstream.

The USB-audio mixer code holds a linked list of usb_mixer_elem_list,
and several operations are performed for each mixer element. A few of
them (snd_usb_mixer_notify_id() and snd_usb_mixer_interrupt_v2())
assume each mixer element being a usb_mixer_elem_info object that is a
subclass of usb_mixer_elem_list, cast via container_of() and access it
members. This may result in an out-of-bound access when a
non-standard list element has been added, as spotted by syzkaller
recently.

This patch adds a new field, is_std_info, in usb_mixer_elem_list to
indicate that the element is the usb_mixer_elem_info type or not, and
skip the access to such an element if needed.

Reported-by: syzbot+fb14314433463ad51625@syzkaller.appspotmail.com
Reported-by: syzbot+2405ca3401e943c538b5@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200624122340.9615-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/mixer.c | 15 +++++++++++----
sound/usb/mixer.h | 9 +++++++--
sound/usb/mixer_quirks.c | 3 ++-
3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 8a0211131fc6f..45bd3d54be54b 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -591,8 +591,9 @@ static int check_matrix_bitmap(unsigned char *bmap,
* if failed, give up and free the control instance.
*/

-int snd_usb_mixer_add_control(struct usb_mixer_elem_list *list,
- struct snd_kcontrol *kctl)
+int snd_usb_mixer_add_list(struct usb_mixer_elem_list *list,
+ struct snd_kcontrol *kctl,
+ bool is_std_info)
{
struct usb_mixer_interface *mixer = list->mixer;
int err;
@@ -606,6 +607,7 @@ int snd_usb_mixer_add_control(struct usb_mixer_elem_list *list,
return err;
}
list->kctl = kctl;
+ list->is_std_info = is_std_info;
list->next_id_elem = mixer->id_elems[list->id];
mixer->id_elems[list->id] = list;
return 0;
@@ -3232,8 +3234,11 @@ void snd_usb_mixer_notify_id(struct usb_mixer_interface *mixer, int unitid)
unitid = delegate_notify(mixer, unitid, NULL, NULL);

for_each_mixer_elem(list, mixer, unitid) {
- struct usb_mixer_elem_info *info =
- mixer_elem_list_to_info(list);
+ struct usb_mixer_elem_info *info;
+
+ if (!list->is_std_info)
+ continue;
+ info = mixer_elem_list_to_info(list);
/* invalidate cache, so the value is read from the device */
info->cached = 0;
snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
@@ -3313,6 +3318,8 @@ static void snd_usb_mixer_interrupt_v2(struct usb_mixer_interface *mixer,

if (!list->kctl)
continue;
+ if (!list->is_std_info)
+ continue;

info = mixer_elem_list_to_info(list);
if (count > 1 && info->control != control)
diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 15ec90e96d4d9..f7e6fe1a96f9c 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -59,6 +59,7 @@ struct usb_mixer_elem_list {
struct usb_mixer_elem_list *next_id_elem; /* list of controls with same id */
struct snd_kcontrol *kctl;
unsigned int id;
+ bool is_std_info;
usb_mixer_elem_dump_func_t dump;
usb_mixer_elem_resume_func_t resume;
};
@@ -96,8 +97,12 @@ void snd_usb_mixer_notify_id(struct usb_mixer_interface *mixer, int unitid);
int snd_usb_mixer_set_ctl_value(struct usb_mixer_elem_info *cval,
int request, int validx, int value_set);

-int snd_usb_mixer_add_control(struct usb_mixer_elem_list *list,
- struct snd_kcontrol *kctl);
+int snd_usb_mixer_add_list(struct usb_mixer_elem_list *list,
+ struct snd_kcontrol *kctl,
+ bool is_std_info);
+
+#define snd_usb_mixer_add_control(list, kctl) \
+ snd_usb_mixer_add_list(list, kctl, true)

void snd_usb_mixer_elem_init_std(struct usb_mixer_elem_list *list,
struct usb_mixer_interface *mixer,
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 983e8a3ebfcfe..21c1135bb89b4 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -168,7 +168,8 @@ static int add_single_ctl_with_resume(struct usb_mixer_interface *mixer,
return -ENOMEM;
}
kctl->private_free = snd_usb_mixer_elem_free;
- return snd_usb_mixer_add_control(list, kctl);
+ /* don't use snd_usb_mixer_add_control() here, this is a special list element */
+ return snd_usb_mixer_add_list(list, kctl, false);
}

/*
--
2.25.1