[NET]: Require CAP_NET_ADMIN to create tuntap devices.

The tuntap driver allows an admin to create persistent devices and
assign ownership of them to individual users. Unfortunately, relaxing
the permissions on the /dev/net/tun device node so that they can
actually use those devices will _also_ allow those users to create
arbitrary new devices of their own. This patch corrects that, and
adjusts the recommended permissions for the device node accordingly.

Signed-off-By: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 10 insertions, 4 deletions

diff --git a/Documentation/networking/tuntap.txt b/Documentation/networking/tuntap.txt
index 76750fb9151a..839cbb71388b 100644
--- a/Documentation/networking/tuntap.txt
+++ b/Documentation/networking/tuntap.txt
@@ -39,10 +39,13 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
      mknod /dev/net/tun c 10 200
   
   Set permissions:
-     e.g. chmod 0700 /dev/net/tun
-     if you want the device only accessible by root. Giving regular users the
-     right to assign network devices is NOT a good idea. Users could assign
-     bogus network interfaces to trick firewalls or administrators.
+     e.g. chmod 0666 /dev/net/tun
+     There's no harm in allowing the device to be accessible by non-root users,
+     since CAP_NET_ADMIN is required for creating network devices or for 
+     connecting to network devices which aren't owned by the user in question.
+     If you want to create persistent devices and give ownership of them to 
+     unprivileged users, then you need the /dev/net/tun device to be usable by
+     those users.
 
   Driver module autoloading
 
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a1ed2d983740..6c62d5c88268 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -490,6 +490,9 @@ static int tun_set_iff(struct file *file, struct ifreq *ifr)
 
                 err = -EINVAL;
 
+                if (!capable(CAP_NET_ADMIN))
+                        return -EPERM;
+
                 /* Set dev type */
                 if (ifr->ifr_flags & IFF_TUN) {
                         /* TUN device */