Commit 220345e9 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

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



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: default avatar <syzbot+fb14314433463ad51625@syzkaller.appspotmail.com>
Reported-by: default avatar <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: default avatarTakashi Iwai <tiwai@suse.de>
parent a32a1fc9

sound/usb/mixer.c

+11 −4
Original line number Diff line number Diff line
@@ -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)

sound/usb/mixer.h

+7 −2
Original line number Diff line number Diff line
@@ -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,

sound/usb/mixer_quirks.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

}



/*

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