[PATCH net v2] rtnetlink: always put ILFA_LINK for links with a link-netnsid

[Sabrina Dubroca]

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.

Analyzed-by: Dan Winship <d...@redhat.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
Acked-by: Nicolas Dichtel <nicolas.dich...@6wind.com>
---
v2: change Fixes tag, it's been here forever as Nicolas said, and add his Ack

 net/core/rtnetlink.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 2bd12afb9297..adcc045952c2 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1496,14 +1496,15 @@ static int put_master_ifindex(struct sk_buff *skb, 
struct net_device *dev)
        return ret;
 }
 
-static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev)
+static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev,
+                         bool force)
 {
        int ifindex = dev_get_iflink(dev);
 
-       if (dev->ifindex == ifindex)
-               return 0;
+       if (force || dev->ifindex != ifindex)
+               return nla_put_u32(skb, IFLA_LINK, ifindex);
 
-       return nla_put_u32(skb, IFLA_LINK, ifindex);
+       return 0;
 }
 
 static noinline_for_stack int nla_put_ifalias(struct sk_buff *skb,
@@ -1520,6 +1521,8 @@ static int rtnl_fill_link_netnsid(struct sk_buff *skb,
                                  const struct net_device *dev,
                                  struct net *src_net)
 {
+       bool put_iflink = false;
+
        if (dev->rtnl_link_ops && dev->rtnl_link_ops->get_link_net) {
                struct net *link_net = dev->rtnl_link_ops->get_link_net(dev);
 
@@ -1528,10 +1531,12 @@ static int rtnl_fill_link_netnsid(struct sk_buff *skb,
 
                        if (nla_put_s32(skb, IFLA_LINK_NETNSID, id))
                                return -EMSGSIZE;
+
+                       put_iflink = true;
                }
        }
 
-       return 0;
+       return nla_put_iflink(skb, dev, put_iflink);
 }
 
 static int rtnl_fill_link_af(struct sk_buff *skb,
@@ -1617,7 +1622,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 #ifdef CONFIG_RPS
            nla_put_u32(skb, IFLA_NUM_RX_QUEUES, dev->num_rx_queues) ||
 #endif
-           nla_put_iflink(skb, dev) ||
            put_master_ifindex(skb, dev) ||
            nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
            (dev->qdisc &&
-- 
2.21.0