CVE-2026-80829: ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output()

CVE-2026-80829: ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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.

The Linux kernel CVE team has assigned CVE-2026-80829 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.10.269 with commit 558fc4485ecc704edfe7876d6cebae4738ff7ef8
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.220 with commit 9c8212436631b0063cb021e9f58df438e3db84d0
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.187 with commit e9c00d7533f99aa9833c4b598f47e3b3202fdb9a
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.156 with commit 94e4562fcc81badd1d467ddfb88c27e4fae974c2
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.108 with commit 7639ec9755d3ec0ec8cd7c0fdd2c3d3997434870
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.49 with commit 91919b3b99ab7ce3d7dbb39fcf7c6c742a663c0c
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.13 with commit 7f00dbddb51f4f74325cdc7c3f6b19fb3392481a
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2.3 with commit 1074c2306901b44ebcb83855583c6776e1e392ea
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.3-rc1 with commit 1035a8f63bae28e498b0e7b5ac91d749844a7158

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-2026-80829
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/midi.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/558fc4485ecc704edfe7876d6cebae4738ff7ef8
	https://git.kernel.org/stable/c/9c8212436631b0063cb021e9f58df438e3db84d0
	https://git.kernel.org/stable/c/e9c00d7533f99aa9833c4b598f47e3b3202fdb9a
	https://git.kernel.org/stable/c/94e4562fcc81badd1d467ddfb88c27e4fae974c2
	https://git.kernel.org/stable/c/7639ec9755d3ec0ec8cd7c0fdd2c3d3997434870
	https://git.kernel.org/stable/c/91919b3b99ab7ce3d7dbb39fcf7c6c742a663c0c
	https://git.kernel.org/stable/c/7f00dbddb51f4f74325cdc7c3f6b19fb3392481a
	https://git.kernel.org/stable/c/1074c2306901b44ebcb83855583c6776e1e392ea
	https://git.kernel.org/stable/c/1035a8f63bae28e498b0e7b5ac91d749844a7158