CVE-2026-80829

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

ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output()

snd_usbmidi_novation_output() lays out a two-byte header at

transfer_buffer[0..1] and passes &transfer_buffer[2] together with a

length of ep->max_transfer - 2 to snd_rawmidi_transmit():

count = snd_rawmidi_transmit(ep->ports[0].substream,

&transfer_buffer[2],

ep->max_transfer - 2);

ep->max_transfer comes from the output endpoint's wMaxPacketSize via

usb_maxpacket(). A malformed or malicious device can advertise a bulk

OUT endpoint with a wMaxPacketSize of 1 - the USB core only clamps this

value downwards - so ep->max_transfer becomes 1 and the count argument

becomes -1.

snd_rawmidi_transmit() passes the negative count on to

__snd_rawmidi_transmit_peek(), where "if (count1 > count) count1 = count"

leaves count1 negative; get_aligned_size() keeps it negative for a

byte-stream substream, so the following memcpy(buffer, ..., count1) runs

with a (size_t)-1 length and writes far past the transfer buffer, which

was allocated with usb_alloc_coherent(ep->max_transfer).

This is the same class of bug that was fixed for snd_usbmidi_akai_output()

in commit 0970274613fb ("ALSA: usb-audio: fix OOB write in

snd_usbmidi_akai_output()"); the novation output routine was left

unguarded. Bail out when the endpoint cannot hold the two-byte header

plus at least one payload byte.