net: split out SIOCDEVPRIVATE handling from dev_ioctl

SIOCDEVPRIVATE ioctl commands are mainly used in really old
drivers, and they have a number of problems:

- They hide behind the normal .ndo_do_ioctl function that
  is also used for other things in modern drivers, so it's
  hard to spot a driver that actually uses one of these

- Since drivers use a number different calling conventions,
  it is impossible to support compat mode for them in
  a generic way.

- With all drivers using the same 16 commands codes, there
  is no way to introspect the data being passed through
  things like strace.

Add a new net_device_ops callback pointer, to address the
first two of these. Separating them from .ndo_do_ioctl
makes it easy to grep for drivers with a .ndo_siocdevprivate
callback, and the unwieldy name hopefully makes it easier
to spot in code review.

By passing the ifreq structure and the ifr_data pointer
separately, it is no longer necessary to overload these,
and the driver can use either one for a given command.

Cc: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/netdevices.rst

@@ -222,6 +222,13 @@ ndo_do_ioctl:
 	Synchronization: rtnl_lock() semaphore.
 	Context: process
 
+ndo_siocdevprivate:
+	Synchronization: rtnl_lock() semaphore.
+	Context: process
+
+	This is used to implement SIOCDEVPRIVATE ioctl helpers.
+	These should not be added to new drivers, so don't use.
+
 ndo_get_stats:
 	Synchronization: rtnl_lock() semaphore, dev_base_lock rwlock, or RCU.
 	Context: atomic (can't sleep under rwlock or RCU)

include/linux/netdevice.h

@@ -1361,6 +1361,9 @@ struct net_device_ops {
 	int			(*ndo_validate_addr)(struct net_device *dev);
 	int			(*ndo_do_ioctl)(struct net_device *dev,
 					        struct ifreq *ifr, int cmd);
+	int			(*ndo_siocdevprivate)(struct net_device *dev,
+						      struct ifreq *ifr,
+						      void __user *data, int cmd);
 	int			(*ndo_set_config)(struct net_device *dev,
 					          struct ifmap *map);
 	int			(*ndo_change_mtu)(struct net_device *dev,

net/core/dev_ioctl.c

@@ -259,6 +259,23 @@ static int dev_do_ioctl(struct net_device *dev,
 	return err;
 }
 
+static int dev_siocdevprivate(struct net_device *dev,
+			      struct ifreq *ifr, unsigned int cmd)
+{
+	const struct net_device_ops *ops = dev->netdev_ops;
+	void __user *data = ifr->ifr_data;
+
+	if (ops->ndo_siocdevprivate) {
+		if (netif_device_present(dev))
+			return ops->ndo_siocdevprivate(dev, ifr, data, cmd);
+		else
+			return -ENODEV;
+	}
+
+	/* fall back to do_ioctl for drivers not yet converted */
+	return dev_do_ioctl(dev, ifr, cmd);
+}
+
 /*
  *	Perform the SIOCxIFxxx calls, inside rtnl_lock()
  */
@@ -336,9 +353,11 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
 	 *	Unknown or private ioctl
 	 */
 	default:
-		if ((cmd >= SIOCDEVPRIVATE &&
-		    cmd <= SIOCDEVPRIVATE + 15) ||
-		    cmd == SIOCBONDENSLAVE ||
+		if (cmd >= SIOCDEVPRIVATE &&
+		    cmd <= SIOCDEVPRIVATE + 15)
+			return dev_siocdevprivate(dev, ifr, cmd);
+
+		if (cmd == SIOCBONDENSLAVE ||
 		    cmd == SIOCBONDRELEASE ||
 		    cmd == SIOCBONDSETHWADDR ||
 		    cmd == SIOCBONDSLAVEINFOQUERY ||