CVE-2026-74639: ALSA: us144mkii: re-anchor capture URBs on resubmission

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ALSA: us144mkii: re-anchor capture URBs on resubmission

capture_urb_complete() resubmits each capture URB without anchoring it:

	usb_get_urb(urb);
	ret = usb_submit_urb(urb, GFP_ATOMIC);

Anchoring is a property of a submission, not of the URB.  The giveback
path calls usb_unanchor_urb() before urb->complete(), so an URB
resubmitted from its own completion handler is off the anchor.  The
capture URBs are anchored once, at stream start, so from the first
completion onward tascam->capture_anchor is empty.

tascam_free_urbs(), tascam_disconnect(), tascam_suspend() and the
stop-work path all call usb_kill_anchored_urbs(&tascam->capture_anchor)
to reap the capture URBs before anything is freed.  With the anchor empty
those calls return immediately and the URBs stay queued on the host
controller.

tascam_free_urbs() then returns the capture transfer buffers with
usb_free_coherent(), and snd_card_free() releases the snd_card
allocation that embeds tascam (card->private_data).  The controller
completes the queued URBs afterwards, writing device-supplied data into
the freed transfer buffer, and capture_urb_complete() dereferences the
freed driver object.

KASAN on 7.2.0-rc5 (arm64):

  BUG: KASAN: slab-use-after-free in dummy_timer
  Write of size 512 at addr ffff000015b62000
   __asan_memcpy
   dummy_timer
   hrtimer_run_softirq
  Allocated by task 64:
   usb_alloc_coherent
   tascam_alloc_urbs
   tascam_probe
  Freed by task 170:
   usb_free_coherent
   tascam_free_urbs
   tascam_disconnect
   usb_unbind_interface

  BUG: KASAN: slab-use-after-free in capture_urb_complete
  Read of size 4 at addr ffff0000170ee878
  Freed by task 170:
   release_card_device
   snd_card_free
   tascam_disconnect

Restore the usb_anchor_urb() between the reference count bump and the
resubmission.  That also makes the handler's usb_unanchor_urb() failure
arm meaningful again and restores usb_kill_anchored_urbs() as a barrier
on the disconnect, suspend and stop-work paths.

The anchoring was removed on the premise that the URB is already anchored
from the initial submission, which does not hold once the first giveback
has run.

Discovered by XBOW, triaged by Baul Lee <[email protected]>

The Linux kernel CVE team has assigned CVE-2026-74639 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.18.39 with commit 16f14f55141d4c55c3f321f93c328fff7cd6860a and fixed in 6.18.45 with commit 7779249561d14b8a17c0c83783225794e24a587d
	Issue introduced in 7.1.4 with commit ab1db64912428cdf06a4f9542e16e0575e9ad59f and fixed in 7.1.9 with commit a5548ce916594c811bd90ce33d67baa3557a6791

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74639
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	sound/usb/usx2y/us144mkii_capture.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/7779249561d14b8a17c0c83783225794e24a587d
	https://git.kernel.org/stable/c/a5548ce916594c811bd90ce33d67baa3557a6791
	https://git.kernel.org/stable/c/2615f0fb90df8cf5a96133ca4be74294ed288604