CVE-2026-80973

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

ALSA: 6fire: bound the MIDI event length from the device

usb6fire_comm_receiver_handler() forwards a MIDI event using a length

byte the device supplies, with no bound and no check that the transfer

delivered that many bytes:

if (!urb->status) {

if (rt->receiver_buffer[0] == 0x10) /* midi in event */

if (midi_rt)

midi_rt->in_received(midi_rt,

rt->receiver_buffer + 2,

rt->receiver_buffer[1]);

}

receiver_buffer is a 64-byte kzalloc() buffer (COMM_RECEIVER_BUFSIZE), so

only 62 bytes follow the two-byte header. receiver_buffer[1] is a u8 the

device chooses, so a device that answers with 0x10 and a length of 0xFF

makes snd_rawmidi_receive() read 255 bytes starting two bytes into a

64-byte object. The bytes past the buffer are handed to userspace

through the rawmidi read path.

urb->actual_length is not consulted either, so a short transfer leaves

both the type byte and the length byte at their previous values and the

handler acts on stale data.

The receiver URB is submitted from usb6fire_comm_init() at probe, so the

read happens on plug with no user action; forwarding to userspace also

needs a MIDI input substream open, since usb6fire_midi_in_received()

only calls snd_rawmidi_receive() when rt->in is set.

KASAN on 7.2.0-rc5 (arm64), single packet from an emulated device:

BUG: KASAN: slab-out-of-bounds in snd_rawmidi_receive

Read of size 255 at addr ffff000009f64682 by task bash/183

__asan_memcpy

snd_rawmidi_receive

usb6fire_midi_in_received [snd_usb_6fire]

usb6fire_comm_receiver_handler [snd_usb_6fire]

Allocated by task 11:

usb6fire_comm_init [snd_usb_6fire]

usb6fire_chip_probe [snd_usb_6fire]

The buggy address is located 2 bytes inside of

allocated 64-byte region [ffff000009f64680, ffff000009f646c0)

Reject the event when the length exceeds the bytes that follow the

header, and require the transfer to have delivered the header plus that

many bytes. The receiver URB is submitted with a 64-byte

transfer_buffer_length, so a genuine device cannot deliver an event

longer than those 62 bytes and nothing valid is dropped.

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