[PATCH AUTOSEL 3.18 04/22] tun: Consistently configure generic netdev params via rtnetlink

[Sasha Levin <sashal@kernel.org>]

From: Serhey Popovych <serhe.popovych@gmail.com>

[ Upstream commit df52eab23d703142c766ac00bdb8db19d71238d0 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/tun.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3067f840210e..7448ebe2c383 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1423,6 +1423,8 @@ static void tun_setup(struct net_device *dev)
  */
 static int tun_validate(struct nlattr *tb[], struct nlattr *data[])
 {
+	if (!data)
+		return 0;
 	return -EINVAL;
 }
 
-- 
2.17.1