net: vlan: Avoid using strncpy()

Use strscpy_pad() instead of strncpy() which is considered deprecated:
https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan.c

@@ -638,7 +638,8 @@ static int vlan_ioctl_handler(struct net *net, void __user *arg)
 
 	case GET_VLAN_REALDEV_NAME_CMD:
 		err = 0;
-		vlan_dev_get_realdev_name(dev, args.u.device2);
+		vlan_dev_get_realdev_name(dev, args.u.device2,
+					  sizeof(args.u.device2));
 		if (copy_to_user(arg, &args,
 				 sizeof(struct vlan_ioctl_args)))
 			err = -EFAULT;

net/8021q/vlan.h

@@ -129,7 +129,8 @@ void vlan_dev_set_ingress_priority(const struct net_device *dev,
 int vlan_dev_set_egress_priority(const struct net_device *dev,
 				 u32 skb_prio, u16 vlan_prio);
 int vlan_dev_change_flags(const struct net_device *dev, u32 flag, u32 mask);
-void vlan_dev_get_realdev_name(const struct net_device *dev, char *result);
+void vlan_dev_get_realdev_name(const struct net_device *dev, char *result,
+			       size_t size);
 
 int vlan_check_real_dev(struct net_device *real_dev,
 			__be16 protocol, u16 vlan_id,

net/8021q/vlan_dev.c

@@ -239,9 +239,9 @@ int vlan_dev_change_flags(const struct net_device *dev, u32 flags, u32 mask)
 	return 0;
 }
 
-void vlan_dev_get_realdev_name(const struct net_device *dev, char *result)
+void vlan_dev_get_realdev_name(const struct net_device *dev, char *result, size_t size)
 {
-	strncpy(result, vlan_dev_priv(dev)->real_dev->name, 23);
+	strscpy_pad(result, vlan_dev_priv(dev)->real_dev->name, size);
 }
 
 bool vlan_dev_inherit_address(struct net_device *dev,
@@ -360,7 +360,7 @@ static int vlan_dev_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	struct ifreq ifrr;
 	int err = -EOPNOTSUPP;
 
-	strncpy(ifrr.ifr_name, real_dev->name, IFNAMSIZ);
+	strscpy_pad(ifrr.ifr_name, real_dev->name, IFNAMSIZ);
 	ifrr.ifr_ifru = ifr->ifr_ifru;
 
 	switch (cmd) {