Re: [PATCH net 2/5] net: check for altname conflicts when changing netdev's netns

[Jiri Pirko <jiri@resnulli.us>]

Mon, Oct 16, 2023 at 10:16:54PM CEST, kuba@kernel.org wrote:
>It's currently possible to create an altname conflicting
>with an altname or real name of another device by creating
>it in another netns and moving it over:
>
> [ ~]$ ip link add dev eth0 type dummy
>
> [ ~]$ ip netns add test
> [ ~]$ ip -netns test link add dev ethX netns test type dummy
> [ ~]$ ip -netns test link property add dev ethX altname eth0
> [ ~]$ ip -netns test link set dev ethX netns 1
>
> [ ~]$ ip link
> ...
> 3: eth0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
>     link/ether 02:40:88:62:ec:b8 brd ff:ff:ff:ff:ff:ff
> ...
> 5: ethX: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
>     link/ether 26:b7:28:78:38:0f brd ff:ff:ff:ff:ff:ff
>     altname eth0
>
>Create a macro for walking the altnames, this hopefully makes
>it clearer that the list we walk contains only altnames.
>Which is otherwise not entirely intuitive.
>
>Fixes: 36fbf1e52bd3 ("net: rtnetlink: add linkprop commands to add and delete alternative ifnames")
>Signed-off-by: Jakub Kicinski <kuba@kernel.org>
>---
>CC: gnault@redhat.com
>CC: liuhangbin@gmail.com
>CC: lucien.xin@gmail.com
>CC: jiri@resnulli.us
>---
> net/core/dev.c | 9 ++++++++-
> net/core/dev.h | 3 +++
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
>diff --git a/net/core/dev.c b/net/core/dev.c
>index b08031957ffe..f4fa2692cf6d 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -1086,7 +1086,8 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
> 
> 		for_each_netdev(net, d) {
> 			struct netdev_name_node *name_node;
>-			list_for_each_entry(name_node, &d->name_node->list, list) {
>+
>+			netdev_for_each_altname(d, name_node) {

Well, cleaner would be to do this in a separate patch and the fix itself
too.

One way or another, code looks fine.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>

Thanks!


> 				if (!sscanf(name_node->name, name, &i))
> 					continue;
> 				if (i < 0 || i >= max_netdevices)
>@@ -11047,6 +11048,7 @@ EXPORT_SYMBOL(unregister_netdev);
> int __dev_change_net_namespace(struct net_device *dev, struct net *net,
> 			       const char *pat, int new_ifindex)
> {
>+	struct netdev_name_node *name_node;
> 	struct net *net_old = dev_net(dev);
> 	char new_name[IFNAMSIZ] = {};
> 	int err, new_nsid;
>@@ -11079,6 +11081,11 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
> 		if (err < 0)
> 			goto out;
> 	}
>+	/* Check that none of the altnames conflicts. */
>+	err = -EEXIST;
>+	netdev_for_each_altname(dev, name_node)
>+		if (netdev_name_in_use(net, name_node->name))
>+			goto out;
> 
> 	/* Check that new_ifindex isn't used yet. */
> 	if (new_ifindex) {
>diff --git a/net/core/dev.h b/net/core/dev.h
>index e075e198092c..d093be175bd0 100644
>--- a/net/core/dev.h
>+++ b/net/core/dev.h
>@@ -62,6 +62,9 @@ struct netdev_name_node {
> int netdev_get_name(struct net *net, char *name, int ifindex);
> int dev_change_name(struct net_device *dev, const char *newname);
> 
>+#define netdev_for_each_altname(dev, name_node)				\
>+	list_for_each_entry((name_node), &(dev)->name_node->list, list)
>+
> int netdev_name_node_alt_create(struct net_device *dev, const char *name);
> int netdev_name_node_alt_destroy(struct net_device *dev, const char *name);
> 
>-- 
>2.41.0
>