[PATCH 5.0 010/139] rtnetlink: always put IFLA_LINK for links with a link-netnsid

Greg Kroah-Hartman
2019-05-23T19:19:49Z

From: Sabrina Dubroca <sd@queasysnail.net>

[ Upstream commit feadc4b6cf42a53a8a93c918a569a0b7e62bd350 ]

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

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/rtnetlink.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1502,14 +1502,15 @@ static int put_master_ifindex(struct sk_
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,
@@ -1526,6 +1527,8 @@ static int rtnl_fill_link_netnsid(struct
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);

@@ -1534,10 +1537,12 @@ static int rtnl_fill_link_netnsid(struct

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,
@@ -1623,7 +1628,6 @@ static int rtnl_fill_ifinfo(struct sk_bu
#ifdef CONFIG_RPS
nla_put_u32(skb, IFLA_NUM_RX_QUEUES, dev->num_rx_queues) ||
#endif
- nla_put_iflink(skb, dev) ||
put_master_ifindex(skb, dev) ||
nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
(dev->qdisc &&