tun: Consistently configure generic netdev params via rtnetlink

Configuring generic network device parameters on tun will fail in
presence of IFLA_INFO_KIND attribute in IFLA_LINKINFO nested attribute
since tun_validate() always return failure.

This can be visualized with following ip-link(8) command sequences:

  # ip link set dev tun0 group 100
  # ip link set dev tun0 group 100 type tun
  RTNETLINK answers: Invalid argument

with contrast to dummy and veth drivers:

  # ip link set dev dummy0 group 100
  # ip link set dev dummy0 type dummy

  # ip link set dev veth0 group 100
  # ip link set dev veth0 group 100 type veth

Fix by returning zero in tun_validate() when @data is NULL that is
always in case since rtnl_link_ops->maxtype is zero in tun driver.

Fixes: f019a7a594d9 ("tun: Implement ip link del tunXXX")
Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 92fa35abba92..060135ceaf0e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2289,6 +2289,8 @@ static void tun_setup(struct net_device *dev)
 static int tun_validate(struct nlattr *tb[], struct nlattr *data[],
                         struct netlink_ext_ack *extack)
 {
+        if (!data)
+                return 0;
         return -EINVAL;
 }