Re: [PATCH 3.18 08/19] ALSA: usb-audio: Kill stray URB at exiting

[Greg Kroah-Hartman]

On Mon, Oct 16, 2017 at 08:50:02PM +0200, Takashi Iwai wrote:
> On Mon, 16 Oct 2017 18:11:59 +0200,
> Greg Kroah-Hartman wrote:
> > 
> > 3.18-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Takashi Iwai <tiwai@xxxxxxx>
> > 
> > commit 124751d5e63c823092060074bd0abaae61aaa9c4 upstream.
> > 
> > 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@xxxxxxxxxx>
> > Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > 
> > ---
> >  sound/usb/mixer.c |   12 ++++++++++--
> >  sound/usb/mixer.h |    2 ++
> >  2 files changed, 12 insertions(+), 2 deletions(-)
> > 
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -2157,6 +2157,9 @@ static int parse_audio_unit(struct mixer
> >  
> >  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);
> > @@ -2501,8 +2504,13 @@ void snd_usb_mixer_disconnect(struct lis
> >  /* stop any bus activity of a mixer */
> >  static void snd_usb_mixer_inactivate(struct usb_mixer_interface *mixer)
> >  {
> > -	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;
> 
> This looks applied wrongly, as already caught by kbuild bot.
> The snd_usb_mixer_disconnect() argument changed in the later kernel,
> thus the patch couldn't be applied cleanly as is.
> 
> Below is the revised patch (but only compile-tested).

Ah, my fault for missing the build warning, thanks for the update, now
applied and pushed out.

greg k-h