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

Overview

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

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

snd_usbmidi_akai_output() computes its fill-loop bound

buf_end = ep->max_transfer - MAX_AKAI_SYSEX_LEN - 1;

as a signed int, so a small device-advertised bulk-OUT max_transfer makes buf_end negative. The loop guard then compares the u32 urb->transfer_buffer_length against that negative int: the usual arithmetic conversion turns buf_end into a large unsigned value, so the guard stays true and each iteration keeps appending SysEx framing and payload bytes past the end of the URB transfer buffer, which is only max_transfer bytes long.

A USB device that advertises a tiny bulk-OUT endpoint can therefore trigger an attacker-length- and content-controlled heap out-of-bounds write when a process writes to the created /dev/snd/midiCD node.

Return early when there is no room for even one SysEx, so the loop is never entered with a bound that would wrap. The loop is the last statement of the function, so bailing out is equivalent to it not running.

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

Affected

• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 78dfdeb8d2065524ed5928d6470bf3d3244d1009
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 00cc659a42ac4e94ec880fae2c9bf22fce69c2e8
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < ce949d66607cfb000b8d8d84f80f35a886e72683
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 29a4c29943631301e85f5e9d10f25741bd78e7ba
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 9b22a5c8310b0d55d04f5f0159b913a2fb8b444f
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < b5305a0d0bb8e90a6fc9f88270d5f6c9b8c40081
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 2b7a0f330dd90dd1a7657cec0db019ee1efa4372
• Linux >= 4434ade8c9334a3ab975d8993de456f06841899e < 0970274613fb463d376211450cab066d34ebfe6a
• Linux 2.6.35

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.