Implement ifnet cloning for tun(4)/tap(4).

Make devfs cloning a sysctl/tunable which defaults to on.

If devfs cloning is enabled, only the super-user may create
tun(4)/tap(4)/vmnet(4) instances. Devfs cloning is still enabled by
default; it may be disabled from the loader or via sysctl with
"net.link.tap.devfs_cloning" and "net.link.tun.devfs_cloning".

Disabling its use affects potentially all tun(4)/tap(4) consumers
including OpenSSH, OpenVPN and VMware.

PR:		105228 (potentially also 90413, 105570)
Submitted by:	Landon Fuller
Tested by:	Andrej Tobola
Approved by:	core (rwatson)
MFC after:	4 weeks

1 files changed, 33 insertions, 4 deletions

diff --git a/share/man/man4/tun.4 b/share/man/man4/tun.4
index d6dd862..e162ef4 100644
--- a/share/man/man4/tun.4
+++ b/share/man/man4/tun.4
@@ -2,7 +2,7 @@
 .\" $FreeBSD$
 .\" Based on PR#2411
 .\"
-.Dd October 9, 2006
+.Dd February 4, 2007
 .Dt TUN 4
 .Os
 .Sh NAME
@@ -42,11 +42,28 @@ The network interfaces are named
 etc., one for each control device that has been opened.
 These network interfaces persist until the
 .Pa if_tun.ko
-module is unloaded (if
+module is unloaded, or until removed with the
+.Xr ifconfig 8
+command.
+.Pp
+.Nm
+devices are created using interface cloning.
+This is done using the
+.Dq ifconfig tap Ns Sy N No create
+command.
+This is the preferred method of creating
 .Nm
-is built into your kernel, the network interfaces cannot be removed).
+devices.
+The same method allows removal of interfaces.
+For this, use the
+.Dq ifconfig tap Ns Sy N No destroy
+command.
 .Pp
-The
+If the
+.Xr sysctl 8
+variable
+.Va net.link.tun.devfs_cloning
+is non-zero, the
 .Nm
 interface
 permits opens on the special control device
@@ -58,6 +75,18 @@ will return a handle for the lowest unused
 device (use
 .Xr devname 3
 to determine which).
+.Pp
+.Bf Em
+Disabling the legacy devfs cloning functionality may break existing
+applications which use
+.Nm ,
+such as
+.Xr ppp 8
+and
+.Xr ssh 1 .
+It therefore defaults to being enabled until further notice.
+.Ef
+.Pp
 Control devices (once successfully opened) persist until
 .Pa if_tun.ko
 is unloaded in the same way that network interfaces persist (see above).