On 5/13/19 7:47 AM, Sabrina Dubroca wrote:
> 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,
why not always adding the attribute?
