wifi: carl9170: bound memcpy length in cmd callback to prevent OOB read

wifi: carl9170: bound memcpy length in cmd callback to prevent OOB read

When the firmware sends a command response with a length mismatch,
carl9170_cmd_callback() logs the mismatch and calls carl9170_restart()
but then falls through to memcpy(ar->readbuf, buffer + 4, len - 4).
Since len comes from the firmware and can exceed ar->readlen, this
copies more data than the readbuf was allocated for.

Bound the memcpy to min(len - 4, ar->readlen) so that the response
is still completed -- avoiding repeated restarts from queued garbage --
while preventing an overread past the response buffer.

Fixes: a84fab3cbfdc ("carl9170: 802.11 rx/tx processing and usb backend")
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=5c1ca6ccaa1215781cac
Link: https://patch.msgid.link/20260421134929.325662-2-tristmd@gmail.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>