net/core: Allow live renaming when an interface is up

Allow a network interface to be renamed when the interface
is up.

As described in the netconsole documentation [1], when netconsole is
used as a built-in, it will bring up the specified interface as soon as
possible. As a result, user space will not be able to rename the
interface since the kernel disallows renaming of interfaces that are
administratively up unless the 'IFF_LIVE_RENAME_OK' private flag was set
by the kernel.

The original solution [2] to this problem was to add a new parameter to
the netconsole configuration parameters that allows renaming of
the interface used by netconsole while it is administratively up.
However, during the discussion that followed, it became apparent that we
have no reason to keep the current restriction and instead we should
allow user space to rename interfaces regardless of their administrative
state:

1. The restriction was put in place over 20 years ago when renaming was
only possible via IOCTL and before rtnetlink started notifying user
space about such changes like it does today.

2. The 'IFF_LIVE_RENAME_OK' flag was added over 3 years ago in version
5.2 and no regressions were reported.

3. In-kernel listeners to 'NETDEV_CHANGENAME' do not seem to care about
the administrative state of interface.

Therefore, allow user space to rename running interfaces by removing the
restriction and the associated 'IFF_LIVE_RENAME_OK' flag. Help in
possible triage by emitting a message to the kernel log that an
interface was renamed while UP.

[1] https://www.kernel.org/doc/Documentation/networking/netconsole.rst
[2] https://lore.kernel.org/netdev/20221102002420.2613004-1-andy.ren@getcruise.com/

Signed-off-by: Andy Ren <andy.ren@getcruise.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 17 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 3bacee3bee78..707de6b841d0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1163,22 +1163,6 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
 	net = dev_net(dev);
 
-	/* Some auto-enslaved devices e.g. failover slaves are
-	 * special, as userspace might rename the device after
-	 * the interface had been brought up and running since
-	 * the point kernel initiated auto-enslavement. Allow
-	 * live name change even when these slave devices are
-	 * up and running.
-	 *
-	 * Typically, users of these auto-enslaving devices
-	 * don't actually care about slave name change, as
-	 * they are supposed to operate on master interface
-	 * directly.
-	 */
-	if (dev->flags & IFF_UP &&
-	    likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK)))
-		return -EBUSY;
-
 	down_write(&devnet_rename_sem);
 
 	if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
@@ -1195,7 +1179,8 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	}
 
 	if (oldname[0] && !strchr(oldname, '%'))
-		netdev_info(dev, "renamed from %s\n", oldname);
+		netdev_info(dev, "renamed from %s%s\n", oldname,
+			    dev->flags & IFF_UP ? " (while UP)" : "");
 
 	old_assign_type = dev->name_assign_type;
 	dev->name_assign_type = NET_NAME_RENAMED;