-- in-guest build (stock source snapshot), command sequence of build.sh --
$ cd /usr/src/sys/netgraph7/netgraph && make        -> netgraph.ko
$ cd /usr/src/sys/netgraph7/socket && make          -> ng_socket.ko
$ cd /usr/src/sys/netgraph7/hole && make            -> ng_hole.ko
$ cd /usr/src/sys/netgraph7/echo && make            -> ng_echo.ko
$ cc -O2 -o /root/poc58/hole_oob /root/poc58/hole_oob.c
$ cc -O2 -o /root/poc58/echo_neg /root/poc58/echo_neg.c
BUILD_OK

Module builds are -Werror clean (full cc lines in the session log; e.g.
ng_hole.c compiles with the standard KLD_MODULE flag set and links
ng_hole.ko). For the fix build: patch(1) applied both hunks cleanly
("Patching file sys/netgraph7/socket/ng_socket.c using Plan A...",
"Patching file sys/netgraph7/hole/ng_hole.c using Plan A...") and the
two modules rebuilt -Werror clean.