socketcan: support the CANFD_FDF flag for identifying CAN FD frames.

The Linux SocketCAN header now uses the formerly-reserved byte in the
SocketCAN header after the "payload length" field as an "FD flags"
field, with a flag bit reserved to indicate whether the frame is a
classic CAN frame or a CAN FD frame, with two other bits giving frame
information for FD frames.

For LINKTYPE_CAN_SOCKETCAN, use that flag bit to determine whether the
frame is classic CAN or CAN FD.  As some older LINKTYPE_CAN_SOCKETCAN
captures have SocketCAN headers in which the fields after the "payload
length" field were uninitialized, so trust that thge "FD flags" was
filled in, rather than possibly randomly uninitialized, only if the only
bits set in that field are the bits defined to be in that field and the
two reserved bytes after it are zero.

This will be needed when the current main-branch libpcap is released, as
it uses LINKTYPE_CAN_SOCKETCAN rather than LINKTYPE_LINUX_SLL for
ARPHRD_CAN devices; we add it now to future-proof the Wireshark releases
to which this is being committed.  It also handles what existing CAN FD
captures using LINKTYPE_CAN_SOCKETCAN exist.

For LINKTYPE_LINUX_SLL frames, we have the protocol field to distinguish
between classic CAN and CAN FD, so we use that to determine the frame
type, rather than looking at the CANFD_FDF flag.

dissect_socketcan_common() now handles both classic CAN and CAN FD
frames.

0 files changed, 0 insertions, 0 deletions