ACK: [PATCH] ALSA: usb-audio: Kill stray URB at exiting

[Stefan Bader]

On 10.07.2018 16:58, Paolo Pisati wrote:
> From: Takashi Iwai <tiwai at suse.de>
> 
> USB-audio driver may leave a stray URB for the mixer interrupt when it
> exits by some error during probe.  This leads to a use-after-free
> error as spotted by syzkaller like:
>   ==================================================================
>   BUG: KASAN: use-after-free in snd_usb_mixer_interrupt+0x604/0x6f0
>   Call Trace:
>    <IRQ>
>    __dump_stack lib/dump_stack.c:16
>    dump_stack+0x292/0x395 lib/dump_stack.c:52
>    print_address_description+0x78/0x280 mm/kasan/report.c:252
>    kasan_report_error mm/kasan/report.c:351
>    kasan_report+0x23d/0x350 mm/kasan/report.c:409
>    __asan_report_load8_noabort+0x19/0x20 mm/kasan/report.c:430
>    snd_usb_mixer_interrupt+0x604/0x6f0 sound/usb/mixer.c:2490
>    __usb_hcd_giveback_urb+0x2e0/0x650 drivers/usb/core/hcd.c:1779
>    ....
> 
>   Allocated by task 1484:
>    save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
>    save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>    set_track mm/kasan/kasan.c:459
>    kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>    kmem_cache_alloc_trace+0x11e/0x2d0 mm/slub.c:2772
>    kmalloc ./include/linux/slab.h:493
>    kzalloc ./include/linux/slab.h:666
>    snd_usb_create_mixer+0x145/0x1010 sound/usb/mixer.c:2540
>    create_standard_mixer_quirk+0x58/0x80 sound/usb/quirks.c:516
>    snd_usb_create_quirk+0x92/0x100 sound/usb/quirks.c:560
>    create_composite_quirk+0x1c4/0x3e0 sound/usb/quirks.c:59
>    snd_usb_create_quirk+0x92/0x100 sound/usb/quirks.c:560
>    usb_audio_probe+0x1040/0x2c10 sound/usb/card.c:618
>    ....
> 
>   Freed by task 1484:
>    save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
>    save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>    set_track mm/kasan/kasan.c:459
>    kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:524
>    slab_free_hook mm/slub.c:1390
>    slab_free_freelist_hook mm/slub.c:1412
>    slab_free mm/slub.c:2988
>    kfree+0xf6/0x2f0 mm/slub.c:3919
>    snd_usb_mixer_free+0x11a/0x160 sound/usb/mixer.c:2244
>    snd_usb_mixer_dev_free+0x36/0x50 sound/usb/mixer.c:2250
>    __snd_device_free+0x1ff/0x380 sound/core/device.c:91
>    snd_device_free_all+0x8f/0xe0 sound/core/device.c:244
>    snd_card_do_free sound/core/init.c:461
>    release_card_device+0x47/0x170 sound/core/init.c:181
>    device_release+0x13f/0x210 drivers/base/core.c:814
>    ....
> 
> Actually such a URB is killed properly at disconnection when the
> device gets probed successfully, and what we need is to apply it for
> the error-path, too.
> 
> In this patch, we apply snd_usb_mixer_disconnect() at releasing.
> Also introduce a new flag, disconnected, to struct usb_mixer_interface
> for not performing the disconnection procedure twice.
> 
> Reported-by: Andrey Konovalov <andreyknvl at google.com>
> Tested-by: Andrey Konovalov <andreyknvl at google.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> (cherry picked from commit 124751d5e63c823092060074bd0abaae61aaa9c4)
> Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  sound/usb/card.c  |  5 ++++-
>  sound/usb/mixer.c | 17 +++++++++++------
>  sound/usb/mixer.h |  4 +++-
>  3 files changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index ab433a0..abd816d 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -616,7 +616,10 @@ static void snd_usb_audio_disconnect(struct usb_device *dev,
>  		}
>  		/* release mixer resources */
>  		list_for_each(p, &chip->mixer_list) {
> -			snd_usb_mixer_disconnect(p);
> +			struct usb_mixer_interface *mixer;
> +
> +			mixer = list_entry(p, struct usb_mixer_interface, list);
> +			snd_usb_mixer_disconnect(mixer);
>  		}
>  	}
>  
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 43492a6..b369c46 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -2071,6 +2071,9 @@ static int parse_audio_unit(struct mixer_build *state, int unitid)
>  
>  static void snd_usb_mixer_free(struct usb_mixer_interface *mixer)
>  {
> +	/* kill pending URBs */
> +	snd_usb_mixer_disconnect(mixer);
> +
>  	kfree(mixer->id_elems);
>  	if (mixer->urb) {
>  		kfree(mixer->urb->transfer_buffer);
> @@ -2412,11 +2415,13 @@ _error:
>  	return err;
>  }
>  
> -void snd_usb_mixer_disconnect(struct list_head *p)
> +void snd_usb_mixer_disconnect(struct usb_mixer_interface *mixer)
>  {
> -	struct usb_mixer_interface *mixer;
> -
> -	mixer = list_entry(p, struct usb_mixer_interface, list);
> -	usb_kill_urb(mixer->urb);
> -	usb_kill_urb(mixer->rc_urb);
> +	if (mixer->disconnected)
> +		return;
> +	if (mixer->urb)
> +		usb_kill_urb(mixer->urb);
> +	if (mixer->rc_urb)
> +		usb_kill_urb(mixer->rc_urb);
> +	mixer->disconnected = true;
>  }
> diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
> index aab80df..f74a4d6 100644
> --- a/sound/usb/mixer.h
> +++ b/sound/usb/mixer.h
> @@ -23,6 +23,8 @@ struct usb_mixer_interface {
>  
>  	u8 audigy2nx_leds[3];
>  	u8 xonar_u1_status;
> +
> +	bool disconnected;
>  };
>  
>  #define MAX_CHANNELS	16	/* max logical channels */
> @@ -57,7 +59,7 @@ struct usb_mixer_elem_info {
>  
>  int snd_usb_create_mixer(struct snd_usb_audio *chip, int ctrlif,
>  			 int ignore_error);
> -void snd_usb_mixer_disconnect(struct list_head *p);
> +void snd_usb_mixer_disconnect(struct usb_mixer_interface *mixer);
>  
>  void snd_usb_mixer_notify_id(struct usb_mixer_interface *mixer, int unitid);
>  
> 


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