net, compat_ioctl: handle socket ioctl abuses in tty drivers

Slip and a few other drivers use the same ioctl numbers on
tty devices that are normally meant for sockets. This causes
problems with our compat_ioctl handling that tries to convert
the data structures in a different format.

Fortunately, these five drivers all use 32 bit compatible
data structures in the ioctl numbers, so we can just add
a trivial compat_ioctl conversion function to each of them.

SIOCSIFENCAP and SIOCGIFENCAP do not need to live in
fs/compat_ioctl.c after this any more, and they are not
used on any sockets.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/mkiss.c

@@ -36,6 +36,7 @@
 #include <linux/skbuff.h>
 #include <linux/if_arp.h>
 #include <linux/jiffies.h>
+#include <linux/compat.h>
 
 #include <net/ax25.h>
 
@@ -898,6 +899,23 @@ static int mkiss_ioctl(struct tty_struct *tty, struct file *file,
 	return err;
 }
 
+#ifdef CONFIG_COMPAT
+static long mkiss_compat_ioctl(struct tty_struct *tty, struct file *file,
+	unsigned int cmd, unsigned long arg)
+{
+	switch (arg) {
+	case SIOCGIFNAME:
+	case SIOCGIFENCAP:
+	case SIOCSIFENCAP:
+	case SIOCSIFHWADDR:
+		return mkiss_ioctl(tty, file, cmd,
+				   (unsigned long)compat_ptr(arg));
+	}
+
+	return -ENOIOCTLCMD;
+}
+#endif
+
 /*
  * Handle the 'receiver data ready' interrupt.
  * This function is called by the 'tty_io' module in the kernel when
@@ -972,6 +990,9 @@ static struct tty_ldisc_ops ax_ldisc = {
 	.open		= mkiss_open,
 	.close		= mkiss_close,
 	.ioctl		= mkiss_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= mkiss_compat_ioctl,
+#endif
 	.receive_buf	= mkiss_receive_buf,
 	.write_wakeup	= mkiss_write_wakeup
 };