CVE-2026-80971

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

ALSA: bcd2000: clear the URB pointers on disconnect

bcd2000_free_usb_related_resources() frees both URBs and leaves the

pointers behind:

usb_kill_urb(bcd2k->midi_out_urb);

usb_kill_urb(bcd2k->midi_in_urb);

usb_free_urb(bcd2k->midi_out_urb);

usb_free_urb(bcd2k->midi_in_urb);

The rawmidi device outlives that call. A substream that is still open

when the device is unplugged reaches bcd2000_midi_send() from the

trigger path on close. That function writes to the freed URB and then

hands it to the USB core:

bcd2k->midi_out_urb->transfer_buffer_length = BUFSIZE;

...

ret = usb_submit_urb(bcd2k->midi_out_urb, GFP_ATOMIC);

usb_kill_urb() does not stop a later submission either, so a submit that

races the disconnect can requeue the URB after it has been reaped.

midi_in_urb is exposed the same way: bcd2000_input_complete() resubmits

it from the completion handler.

KASAN on 7.2.0-rc5 (arm64):

BUG: KASAN: slab-use-after-free in bcd2000_midi_send [snd_bcd2000]

Write of size 4 at addr ffff00001827d388 by task bpoc/168

__asan_store4

bcd2000_midi_send [snd_bcd2000]

bcd2000_midi_output_trigger [snd_bcd2000]

snd_rawmidi_kernel_write1

close_substream.part.0

Freed by task 168:

usb_free_urb

bcd2000_disconnect [snd_bcd2000]

BUG: KASAN: slab-use-after-free in usb_submit_urb

Read of size 8 at addr ffff00001827d3b8 by task bpoc/168

Clear both pointers after freeing and test them on the paths that can

still run. Poison the URBs before freeing them: usb_poison_urb() waits

for a running completion handler and rejects any later submission, so

after it returns the input path is quiesced and only the rawmidi trigger

path can still reach bcd2000_midi_send(). No unpoison is needed; the

URBs are freed on the next line.

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