Re: [PATCH net-next 1/5] rtnetlink: Lookup device in target netns when creating link

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Xiao Liang <shaw.leon@gmail.com>
Date: Wed, 23 Oct 2024 10:31:42 +0800
> When creating link, lookup for existing device in target net namespace
> instead of current one.
> For example, two links created by:
> 
>   # ip link add dummy1 type dummy
>   # ip link add netns ns1 dummy1 type dummy
> 
> should have no conflict since they are in different namespaces.
> 
> Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
> ---
>  net/core/rtnetlink.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 194a81e5f608..ff8d25acfc00 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3733,20 +3733,24 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>  {
>  	struct nlattr ** const tb = tbs->tb;
>  	struct net *net = sock_net(skb->sk);
> +	struct net *device_net;
>  	struct net_device *dev;
>  	struct ifinfomsg *ifm;
>  	bool link_specified;
>  
> +	/* When creating, lookup for existing device in target net namespace */
> +	device_net = nlh->nlmsg_flags & NLM_F_CREATE ? tgt_net : net;

Technically, this changes uAPI behaviour.

Let's say a user wants to

  1) move the device X in the current netns to another if exists, otherwise
  2) create a new device X in the target netns

This can be achieved by setting NLM_F_CREATE and IFLA_NET_NS_PID,
IFLA_NET_NS_FD, or IFLA_TARGET_NETNSID.

But with this change, the device X in the current netns will not be moved,
and a new device X is created in the target netns.


> +
>  	ifm = nlmsg_data(nlh);
>  	if (ifm->ifi_index > 0) {
>  		link_specified = true;
> -		dev = __dev_get_by_index(net, ifm->ifi_index);
> +		dev = __dev_get_by_index(device_net, ifm->ifi_index);
>  	} else if (ifm->ifi_index < 0) {
>  		NL_SET_ERR_MSG(extack, "ifindex can't be negative");
>  		return -EINVAL;
>  	} else if (tb[IFLA_IFNAME] || tb[IFLA_ALT_IFNAME]) {
>  		link_specified = true;
> -		dev = rtnl_dev_get(net, tb);
> +		dev = rtnl_dev_get(device_net, tb);
>  	} else {
>  		link_specified = false;
>  		dev = NULL;
> -- 
> 2.47.0