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ALSA: usb-audio: Fix OOB access of mixer element list

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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>
This commit is contained in:
Takashi Iwai 2020-06-24 14:23:40 +02:00
parent a32a1fc998
commit 220345e98f
3 changed files with 20 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
sound/usb/mixer.c
View File

@ -581,8 +581,9 @@ 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;
@ -596,6 +597,7 @@ 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;
@ -3234,8 +3236,11 @@ 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,
@ -3315,6 +3320,8 @@ 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)

9
sound/usb/mixer.h
View File

@ -66,6 +66,7 @@ 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;
};
@ -103,8 +104,12 @@ 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,

3
sound/usb/mixer_quirks.c
View File

@ -158,7 +158,8 @@ 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);
}
/*