making tun(4) not IFT_TUNNEL and tap(4) not IFT_ETHER makes for some
interesting possibilities for fun with the rest of the kernel. I think
we should just not allow the if_types to be changed.
I have another diff somewhere to prevent changing the flags
(IFF_BROADCAST etc) somewhere too, but we can start here.
ok?
Index: if_tun.c
===================================================================
RCS file: /cvs/src/sys/net/if_tun.c,v
retrieving revision 1.186
diff -u -p -r1.186 if_tun.c
--- if_tun.c 12 May 2019 16:38:02 -0000 1.186
+++ if_tun.c 10 Jun 2019 06:13:22 -0000
@@ -623,8 +623,9 @@ tun_dev_ioctl(struct tun_softc *tp, u_lo
tunp = (struct tuninfo *)data;
if (tunp->mtu < ETHERMIN || tunp->mtu > TUNMRU)
return (EINVAL);
+ if (tunp->type != tp->tun_if.if_type)
+ return (EINVAL);
tp->tun_if.if_mtu = tunp->mtu;
- tp->tun_if.if_type = tunp->type;
tp->tun_if.if_flags =
(tunp->flags & TUN_IFF_FLAGS) |
(tp->tun_if.if_flags & ~TUN_IFF_FLAGS);
