Patch "ALSA: usb-audio: Kill stray URB at exiting" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: usb-audio: Kill stray URB at exiting

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-usb-audio-kill-stray-urb-at-exiting.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Iwai <[email protected]>
Date: Tue, 10 Oct 2017 14:10:32 +0200
Subject: ALSA: usb-audio: Kill stray URB at exiting

From: Takashi Iwai <[email protected]>

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.

---
 sound/usb/mixer.c |   12 ++++++++++--
 sound/usb/mixer.h |    2 ++
 2 files changed, 12 insertions(+), 2 deletions(-)

@@ -2161,6 +2161,9 @@ 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);

@@ -2504,8 +2507,13 @@ _error:
 
 void snd_usb_mixer_disconnect(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;
 }
 
 #ifdef CONFIG_PM

@@ -22,6 +22,8 @@ struct usb_mixer_interface {
 	struct urb *rc_urb;
 	struct usb_ctrlrequest *rc_setup_packet;
 	u8 rc_buffer[6];
+
+	bool disconnected;
 };
 
 #define MAX_CHANNELS	16	/* max logical channels */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/alsa-caiaq-fix-stray-urb-at-probe-error-path.patch queue-4.4/alsa-seq-fix-copy_from_user-call-inside-lock.patch queue-4.4/alsa-seq-fix-use-after-free-at-creating-a-port.patch queue-4.4/alsa-line6-fix-leftover-urb-at-error-path-during-probe.patch queue-4.4/alsa-usb-audio-kill-stray-urb-at-exiting.patch