Because buflen is size_t (unsigned) and nsent is ssize_t (signed)
of the same size, (buflen - nsent) results in unsigned and
overflows if nsent > buflen.
This happens when sending CAN FD frame with DLC > 8 and a user
gets the buflen parameter as a result of CAN_MSGLEN(len)
where `len' is the size of data which is less then a size
for some extended DLC (e.g. 26 bytes is sent in a message with
DLC 0xD, which has 32 bytes of data).
The correct buflen value should be rather
CAN_MSGLEN(can_dlc2bytes(can_bytes2dlc(len)))
Signed-off-by: Jaroslav Beran <jara.beran@gmail.com>
7c96a25ec1