Like check_access_permissions() but for write_stat() hook instead
of access().
Basic logic copied from BFS, but with the UID/GID logic rewritten
to better conform to behavior on other OSes: notably, we allow
chown() requests that keep the UID the same to go through, same
as Linux seems to, which should fix#19666. We now also validate
that the GID is one of the current team's groups.
Augustin Cavalier
9ea1065b16