An issue was discovered in can_can_gw_rcv in net/can/gw.c in the Linux
kernel through 4.19.13. The CAN frame modification rules allow bitwise
logical operations that can be also applied to the can_dlc field. The
privileged user "root" with CAP_NET_ADMIN can create a CAN frame
modification rule that makes the data length code a higher value than the
available CAN frame data size. In combination with a configured checksum
calculation where the result is stored relatively to the end of the data
(e.g. cgw_csum_xor_rel) the tail of the skb (e.g. frag_list pointer in
skb_shared_info) can be rewritten which finally can cause a system crash.
Because of a missing check, the CAN drivers may write arbitrary content
beyond the data registers in the CAN controller's I/O memory when
processing can-gw manipulated outgoing frames.

Muyu Yu discovered that the CAN implementation in the Linux kernel in some
situations did not properly restrict the field size when processing
outgoing frames. A local attacker with CAP_NET_ADMIN privileges could use
this to execute arbitrary code.

 tyhicks> The original CVE description that states that an unprivileged user
  can trigger a system crash is incorrect. Only the root user, from the init
  namespace, can trigger the system crash. Therefore, we'll prioritize this
  issue as negligible.