Bonding: force user to add HWTSTAMP_FLAG_BONDED_PHC_INDEX when get/set HWTSTAMP

When there is a failover, the PHC index of bond active interface will be
changed. This may break the user space program if the author didn't aware.

By setting this flag, the user should aware that the PHC index get/set
by syscall is not stable. And the user space is able to deal with it.
Without this flag, the kernel will reject the request forwarding to
bonding.
Reported-by: Jakub Kicinski <kuba@kernel.org>
Fixes: 94dd016a ("bond: pass get_ts_info and SIOC[SG]HWTSTAMP ioctl to active device")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -4094,6 +4094,7 @@ static int bond_eth_ioctl(struct net_device *bond_dev, struct ifreq *ifr, int cm
 	struct mii_ioctl_data *mii = NULL;
 	const struct net_device_ops *ops;
 	struct net_device *real_dev;
+	struct hwtstamp_config cfg;
 	struct ifreq ifrr;
 	int res = 0;
 
@@ -4124,21 +4125,29 @@ static int bond_eth_ioctl(struct net_device *bond_dev, struct ifreq *ifr, int cm
 		break;
 	case SIOCSHWTSTAMP:
 	case SIOCGHWTSTAMP:
-		rcu_read_lock();
-		real_dev = bond_option_active_slave_get_rcu(bond);
-		rcu_read_unlock();
-		if (real_dev) {
-			strscpy_pad(ifrr.ifr_name, real_dev->name, IFNAMSIZ);
-			ifrr.ifr_ifru = ifr->ifr_ifru;
+		if (copy_from_user(&cfg, ifr->ifr_data, sizeof(cfg)))
+			return -EFAULT;
+
+		if (cfg.flags & HWTSTAMP_FLAG_BONDED_PHC_INDEX) {
+			rcu_read_lock();
+			real_dev = bond_option_active_slave_get_rcu(bond);
+			rcu_read_unlock();
+			if (real_dev) {
+				strscpy_pad(ifrr.ifr_name, real_dev->name, IFNAMSIZ);
+				ifrr.ifr_ifru = ifr->ifr_ifru;
+
+				ops = real_dev->netdev_ops;
+				if (netif_device_present(real_dev) && ops->ndo_eth_ioctl) {
+					res = ops->ndo_eth_ioctl(real_dev, &ifrr, cmd);
 
-			ops = real_dev->netdev_ops;
-			if (netif_device_present(real_dev) && ops->ndo_eth_ioctl)
-				res = ops->ndo_eth_ioctl(real_dev, &ifrr, cmd);
+					if (!res)
+						ifr->ifr_ifru = ifrr.ifr_ifru;
 
-			if (!res)
-				ifr->ifr_ifru = ifrr.ifr_ifru;
+					return res;
+				}
+			}
 		}
-		break;
+		fallthrough;
 	default:
 		res = -EOPNOTSUPP;
 	}