From: Sabrina Dubroca <sd@queasysnail.net>
Date: Tue, 14 May 2019 15:12:19 +0200
Subject: rtnetlink: always put IFLA_LINK for links with a link-netnsid
Git-commit: feadc4b6cf42a53a8a93c918a569a0b7e62bd350
Patch-mainline: 5.2-rc2
References: networking-stable-19_05_21

Currently, nla_put_iflink() doesn't put the IFLA_LINK attribute when
iflink == ifindex.

In some cases, a device can be created in a different netns with the
same ifindex as its parent. That device will not dump its IFLA_LINK
attribute, which can confuse some userspace software that expects it.
For example, if the last ifindex created in init_net and foo are both
8, these commands will trigger the issue:

    ip link add parent type dummy                   # ifindex 9
    ip link add link parent netns foo type macvlan  # ifindex 9 in ns foo

So, in case a device puts the IFLA_LINK_NETNSID attribute in a dump,
always put the IFLA_LINK attribute as well.

Thanks to Dan Winship for analyzing the original OpenShift bug down to
the missing netlink attribute.

v2: change Fixes tag, it's been here forever, as Nicolas Dichtel said
    add Nicolas' ack
v3: change Fixes tag
    fix subject typo, spotted by Edward Cree

[js] no inlines for the operations in 4.12. Do it directly in the code.

Analyzed-by: Dan Winship <danw@redhat.com>
Fixes: d8a5ec672768 ("[NET]: netlink support for moving devices between network namespaces.")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/core/rtnetlink.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1340,6 +1340,7 @@ static int rtnl_fill_ifinfo(struct sk_bu
 	struct nlattr *af_spec;
 	struct rtnl_af_ops *af_ops;
 	struct net_device *upper_dev = netdev_master_upper_dev_get(dev);
+	bool put_iflink = false;
 
 	ASSERT_RTNL();
 	nlh = nlmsg_put(skb, pid, seq, type, sizeof(*ifm), flags);
@@ -1368,8 +1369,6 @@ static int rtnl_fill_ifinfo(struct sk_bu
 #ifdef CONFIG_RPS
 	    nla_put_u32(skb, IFLA_NUM_RX_QUEUES, dev->num_rx_queues) ||
 #endif
-	    (dev->ifindex != dev_get_iflink(dev) &&
-	     nla_put_u32(skb, IFLA_LINK, dev_get_iflink(dev))) ||
 	    (upper_dev &&
 	     nla_put_u32(skb, IFLA_MASTER, upper_dev->ifindex)) ||
 	    nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
@@ -1449,9 +1448,15 @@ static int rtnl_fill_ifinfo(struct sk_bu
 
 			if (nla_put_s32(skb, IFLA_LINK_NETNSID, id))
 				goto nla_put_failure;
+
+			put_iflink = true;
 		}
 	}
 
+	if ((put_iflink || dev->ifindex != dev_get_iflink(dev)) &&
+	     nla_put_u32(skb, IFLA_LINK, dev_get_iflink(dev)))
+		goto nla_put_failure;
+
 	if (!(af_spec = nla_nest_start(skb, IFLA_AF_SPEC)))
 		goto nla_put_failure;