Possible mistake in commit 3ca459eaba1b ("tun: fix group permission check")

[Ondrej Mosnacek]

Hello,

It looks like the commit in $SUBJ may have introduced an unintended
change in behavior. According to the commit message, the intent was to
require just one of {user, group} to match instead of both, which
sounds reasonable, but the commit also changes the behavior for when
neither of tun->owner and tun->group is set. Before the commit the
access was always allowed, while after the commit CAP_NET_ADMIN is
required in this case.

I'm asking because the tun_tap subtest of selinux-testuite [1] started
to fail after this commit (it assumed CAP_NET_ADMIN was not needed),
so I'm trying to figure out if we need to change the test or if it
needs to be fixed in the kernel.

Thanks,

[1] https://github.com/SELinuxProject/selinux-testsuite/

-- 
Ondrej Mosnacek
Senior Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.