net/compat: Fix minor information leak in siocdevprivate_ioctl()

We don't need to check that ifr_data itself is a valid user pointer,
but we should check &ifr_data is.  Thankfully the copy of ifr_name is
checked, so this can only leak a few bytes from immediately above the
user address limit.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

net/socket.c

@@ -3015,19 +3015,16 @@ static int siocdevprivate_ioctl(struct net *net, unsigned int cmd,
 	if (copy_from_user(&tmp_buf[0], &(u_ifreq32->ifr_ifrn.ifrn_name[0]),
 			   IFNAMSIZ))
 		return -EFAULT;
-	if (__get_user(data32, &u_ifreq32->ifr_ifru.ifru_data))
+	if (get_user(data32, &u_ifreq32->ifr_ifru.ifru_data))
 		return -EFAULT;
 	data64 = compat_ptr(data32);
 
 	u_ifreq64 = compat_alloc_user_space(sizeof(*u_ifreq64));
 
-	/* Don't check these user accesses, just let that get trapped
-	 * in the ioctl handler instead.
-	 */
 	if (copy_to_user(&u_ifreq64->ifr_ifrn.ifrn_name[0], &tmp_buf[0],
 			 IFNAMSIZ))
 		return -EFAULT;
-	if (__put_user(data64, &u_ifreq64->ifr_ifru.ifru_data))
+	if (put_user(data64, &u_ifreq64->ifr_ifru.ifru_data))
 		return -EFAULT;
 
 	return dev_ioctl(net, cmd, u_ifreq64);