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58fc1275b3
snd_caiaq_input_read_erp() and snd_caiaq_input_read_io() can be reached
from snd_usb_caiaq_input_dispatch(). They read fixed byte offsets from
the reply buffer without checking the reported length. On a short reply
they decode stale bytes left from a previous, longer report and feed them
to the input layer.
This is not an out-of-bounds access. Every offset is a compile-time
driver constant. The largest is buf[21] in the Maschine ERP case. The
EP1 transfer buffer ep1_in_buf is EP1_BUFSIZE (64) bytes, and the USB
core caps actual_length at 64, so a short reply only reads in-bounds
stale data. Acting on data the device did not send is still wrong, so
bail out per usb_id case when the reply is shorter than the bytes that
case consumes.
read_erp: AK1 needs 2 bytes, Kore needs 16, Maschine needs 22.
read_io: the Kore case needs 5 bytes (buf[4]) and the Traktor Kontrol
X1 case needs 7 (buf[5]/buf[6]). The preceding key bit loop
is already bounded by "i < len * 8" and is left untouched.
snd_caiaq_input_read_analog() and snd_usb_caiaq_maschine_dispatch() are
not changed. Their callers already floor the reply length.
Suggested-by: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Link: https://patch.msgid.link/178176259547.3343534.6659489917322808916@maoyixie.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>