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.
