net: fix ifname in netlink ntf during netns move

dev_get_valid_name() overwrites the netdev's name on success.
This makes it hard to use in prepare-commit-like fashion,
where we do validation first, and "commit" to the change
later.

Factor out a helper which lets us save the new name to a buffer.
Use it to fix the problem of notification on netns move having
incorrect name:

 5: eth0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
     link/ether be:4d:58:f9:d5:40 brd ff:ff:ff:ff:ff:ff
 6: eth1: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
     link/ether 1e:4a:34:36:e3:cd brd ff:ff:ff:ff:ff:ff

 [ ~]# ip link set dev eth0 netns 1 name eth1

ip monitor inside netns:
 Deleted inet eth0
 Deleted inet6 eth0
 Deleted 5: eth1: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default
     link/ether be:4d:58:f9:d5:40 brd ff:ff:ff:ff:ff:ff new-netnsid 0 new-ifindex 7

Name is reported as eth1 in old netns for ifindex 5, already renamed.

Fixes: d90310243fd7 ("net: device name allocation cleanups")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/dev.c b/net/core/dev.c
index 5aaf575..f109ad3 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1123,6 +1123,26 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
        return -ENFILE;
 }
 
+static int dev_prep_valid_name(struct net *net, struct net_device *dev,
+                              const char *want_name, char *out_name)
+{
+       int ret;
+
+       if (!dev_valid_name(want_name))
+               return -EINVAL;
+
+       if (strchr(want_name, '%')) {
+               ret = __dev_alloc_name(net, want_name, out_name);
+               return ret < 0 ? ret : 0;
+       } else if (netdev_name_in_use(net, want_name)) {
+               return -EEXIST;
+       } else if (out_name != want_name) {
+               strscpy(out_name, want_name, IFNAMSIZ);
+       }
+
+       return 0;
+}
+
 static int dev_alloc_name_ns(struct net *net,
                             struct net_device *dev,
                             const char *name)
@@ -1160,19 +1180,13 @@ EXPORT_SYMBOL(dev_alloc_name);
 static int dev_get_valid_name(struct net *net, struct net_device *dev,
                              const char *name)
 {
-       BUG_ON(!net);
-
-       if (!dev_valid_name(name))
-               return -EINVAL;
-
-       if (strchr(name, '%'))
-               return dev_alloc_name_ns(net, dev, name);
-       else if (netdev_name_in_use(net, name))
-               return -EEXIST;
-       else if (dev->name != name)
-               strscpy(dev->name, name, IFNAMSIZ);
+       char buf[IFNAMSIZ];
+       int ret;
 
-       return 0;
+       ret = dev_prep_valid_name(net, dev, name, buf);
+       if (ret >= 0)
+               strscpy(dev->name, buf, IFNAMSIZ);
+       return ret;
 }
 
 /**
@@ -11038,6 +11052,7 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
                               const char *pat, int new_ifindex)
 {
        struct net *net_old = dev_net(dev);
+       char new_name[IFNAMSIZ] = {};
        int err, new_nsid;
 
        ASSERT_RTNL();
@@ -11064,7 +11079,7 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
                /* We get here if we can't use the current device name */
                if (!pat)
                        goto out;
-               err = dev_get_valid_name(net, dev, pat);
+               err = dev_prep_valid_name(net, dev, pat, new_name);
                if (err < 0)
                        goto out;
        }
@@ -11135,6 +11150,9 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
        kobject_uevent(&dev->dev.kobj, KOBJ_ADD);
        netdev_adjacent_add_links(dev);
 
+       if (new_name[0]) /* Rename the netdev to prepared name */
+               strscpy(dev->name, new_name, IFNAMSIZ);
+
        /* Fixup kobjects */
        err = device_rename(&dev->dev, dev->name);
        WARN_ON(err);