genetlink: start to validate reserved header bytes

We had historically not checked that genlmsghdr.reserved
is 0 on input which prevents us from using those precious
bytes in the future.

One use case would be to extend the cmd field, which is
currently just 8 bits wide and 256 is not a lot of commands
for some core families.

To make sure that new families do the right thing by default
put the onus of opting out of validation on existing families.

Signed-off-by: Jakub Kicinski <[e-mail]>
Acked-by: Paul Moore <[e-mail]> (NetLabel)
Signed-off-by: David S. Miller <[e-mail]>

drivers/block/nbd.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= nbd_connect_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
+	.resv_start_op	= NBD_CMD_STATUS + 1,
 	.maxattr	= NBD_ATTR_MAX,
 	.policy = nbd_attr_policy,
 	.mcgrps		= nbd_mcast_grps,

drivers/net/gtp.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= gtp_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(gtp_genl_ops),
+	.resv_start_op	= GTP_CMD_ECHOREQ + 1,
 	.mcgrps		= gtp_genl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(gtp_genl_mcgrps),
 };

drivers/net/ieee802154/mac802154_hwsim.c

···
 	.module = THIS_MODULE,
 	.small_ops = hwsim_nl_ops,
 	.n_small_ops = ARRAY_SIZE(hwsim_nl_ops),
+	.resv_start_op = MAC802154_HWSIM_CMD_NEW_EDGE + 1,
 	.mcgrps = hwsim_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(hwsim_mcgrps),
 };

drivers/net/macsec.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= macsec_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(macsec_genl_ops),
+	.resv_start_op	= MACSEC_CMD_UPD_OFFLOAD + 1,
 };
 
 static netdev_tx_t macsec_start_xmit(struct sk_buff *skb,

drivers/net/team/team.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= team_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(team_nl_ops),
+	.resv_start_op	= TEAM_CMD_PORT_LIST_GET + 1,
 	.mcgrps		= team_nl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(team_nl_mcgrps),
 };

drivers/net/wireguard/netlink.c

···
 static struct genl_family genl_family __ro_after_init = {
 	.ops = genl_ops,
 	.n_ops = ARRAY_SIZE(genl_ops),
+	.resv_start_op = WG_CMD_SET_DEVICE + 1,
 	.name = WG_GENL_NAME,
 	.version = WG_GENL_VERSION,
 	.maxattr = WGDEVICE_A_MAX,

drivers/net/wireless/mac80211_hwsim.c

···
 	.module = THIS_MODULE,
 	.small_ops = hwsim_ops,
 	.n_small_ops = ARRAY_SIZE(hwsim_ops),
+	.resv_start_op = HWSIM_CMD_DEL_MAC_ADDR + 1,
 	.mcgrps = hwsim_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(hwsim_mcgrps),
 };

drivers/target/target_core_user.c

···
 	.netnsok = true,
 	.small_ops = tcmu_genl_ops,
 	.n_small_ops = ARRAY_SIZE(tcmu_genl_ops),
+	.resv_start_op = TCMU_CMD_SET_FEATURES + 1,
 };
 
 #define tcmu_cmd_set_dbi_cur(cmd, index) ((cmd)->dbi_cur = (index))

drivers/thermal/thermal_netlink.c

···
 	.policy		= thermal_genl_policy,
 	.small_ops	= thermal_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(thermal_genl_ops),
+	.resv_start_op	= THERMAL_GENL_CMD_CDEV_GET + 1,
 	.mcgrps		= thermal_genl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(thermal_genl_mcgrps),
 };

drivers/vdpa/vdpa.c

···
 	.module = THIS_MODULE,
 	.ops = vdpa_nl_ops,
 	.n_ops = ARRAY_SIZE(vdpa_nl_ops),
+	.resv_start_op = VDPA_CMD_DEV_VSTATS_GET + 1,
 };
 
 static int vdpa_init(void)

fs/cifs/netlink.c

···
 	.policy		= cifs_genl_policy,
 	.ops		= cifs_genl_ops,
 	.n_ops		= ARRAY_SIZE(cifs_genl_ops),
+	.resv_start_op	= CIFS_GENL_CMD_SWN_NOTIFY + 1,
 	.mcgrps		= cifs_genl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(cifs_genl_mcgrps),
 };

fs/dlm/netlink.c

···
 	.version	= DLM_GENL_VERSION,
 	.small_ops	= dlm_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(dlm_nl_ops),
+	.resv_start_op	= DLM_CMD_HELLO + 1,
 	.module		= THIS_MODULE,
 };
 

fs/ksmbd/transport_ipc.c

···
 	.module		= THIS_MODULE,
 	.ops		= ksmbd_genl_ops,
 	.n_ops		= ARRAY_SIZE(ksmbd_genl_ops),
+	.resv_start_op	= KSMBD_EVENT_SPNEGO_AUTHEN_RESPONSE + 1,
 };
 
 static void ksmbd_nl_init_fixup(void)

include/linux/genl_magic_func.h

···
 	.ops = ZZZ_genl_ops,
 	.n_ops = ARRAY_SIZE(ZZZ_genl_ops),
 	.mcgrps = ZZZ_genl_mcgrps,
+	.resv_start_op = 42, /* drbd is currently the only user */
 	.n_mcgrps = ARRAY_SIZE(ZZZ_genl_mcgrps),
 	.module = THIS_MODULE,
 };

include/net/genetlink.h

···
  *	undo operations done by pre_doit, for example release locks
  * @mcgrps: multicast groups used by this family
  * @n_mcgrps: number of multicast groups
+ * @resv_start_op: first operation for which reserved fields of the header
+ *	can be validated, new families should leave this field at zero
  * @mcgrp_offset: starting number of multicast group IDs in this family
  *	(private)
  * @ops: the operations supported by this family
···
 	u8			n_ops;
 	u8			n_small_ops;
 	u8			n_mcgrps;
+	u8			resv_start_op;
 	const struct nla_policy *policy;
 	int			(*pre_doit)(const struct genl_ops *ops,
 					    struct sk_buff *skb,

kernel/taskstats.c

···
 	.module		= THIS_MODULE,
 	.ops		= taskstats_ops,
 	.n_ops		= ARRAY_SIZE(taskstats_ops),
+	.resv_start_op	= CGROUPSTATS_CMD_GET + 1,
 	.netnsok	= true,
 };
 

net/batman-adv/netlink.c

···
 	.module = THIS_MODULE,
 	.small_ops = batadv_netlink_ops,
 	.n_small_ops = ARRAY_SIZE(batadv_netlink_ops),
+	.resv_start_op = BATADV_CMD_SET_VLAN + 1,
 	.mcgrps = batadv_netlink_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(batadv_netlink_mcgrps),
 };

net/core/devlink.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= devlink_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(devlink_nl_ops),
+	.resv_start_op	= DEVLINK_CMD_SELFTESTS_RUN + 1,
 	.mcgrps		= devlink_nl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(devlink_nl_mcgrps),
 };

net/core/drop_monitor.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= dropmon_ops,
 	.n_small_ops	= ARRAY_SIZE(dropmon_ops),
+	.resv_start_op	= NET_DM_CMD_STATS_GET + 1,
 	.mcgrps		= dropmon_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(dropmon_mcgrps),
 };

net/ethtool/netlink.c

···
 	.parallel_ops	= true,
 	.ops		= ethtool_genl_ops,
 	.n_ops		= ARRAY_SIZE(ethtool_genl_ops),
+	.resv_start_op	= ETHTOOL_MSG_MODULE_GET + 1,
 	.mcgrps		= ethtool_nl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(ethtool_nl_mcgrps),
 };

net/hsr/hsr_netlink.c

···
 	.module = THIS_MODULE,
 	.small_ops = hsr_ops,
 	.n_small_ops = ARRAY_SIZE(hsr_ops),
+	.resv_start_op = HSR_C_SET_NODE_LIST + 1,
 	.mcgrps = hsr_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(hsr_mcgrps),
 };

net/ieee802154/netlink.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= ieee802154_ops,
 	.n_small_ops	= ARRAY_SIZE(ieee802154_ops),
+	.resv_start_op	= IEEE802154_LLSEC_DEL_SECLEVEL + 1,
 	.mcgrps		= ieee802154_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(ieee802154_mcgrps),
 };

net/ieee802154/nl802154.c

···
 	.module = THIS_MODULE,
 	.ops = nl802154_ops,
 	.n_ops = ARRAY_SIZE(nl802154_ops),
+	.resv_start_op = NL802154_CMD_DEL_SEC_LEVEL + 1,
 	.mcgrps = nl802154_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(nl802154_mcgrps),
 };

net/ipv4/fou.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= fou_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(fou_nl_ops),
+	.resv_start_op	= FOU_CMD_GET + 1,
 };
 
 size_t fou_encap_hlen(struct ip_tunnel_encap *e)

net/ipv4/tcp_metrics.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= tcp_metrics_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(tcp_metrics_nl_ops),
+	.resv_start_op	= TCP_METRICS_CMD_DEL + 1,
 };
 
 static unsigned int tcpmhash_entries;

net/ipv6/ila/ila_main.c

···
 	.module		= THIS_MODULE,
 	.ops		= ila_nl_ops,
 	.n_ops		= ARRAY_SIZE(ila_nl_ops),
+	.resv_start_op	= ILA_CMD_FLUSH + 1,
 };
 
 static __net_init int ila_init_net(struct net *net)

net/ipv6/ioam6.c

···
 	.parallel_ops	= true,
 	.ops		= ioam6_genl_ops,
 	.n_ops		= ARRAY_SIZE(ioam6_genl_ops),
+	.resv_start_op	= IOAM6_CMD_NS_SET_SCHEMA + 1,
 	.module		= THIS_MODULE,
 };
 

net/ipv6/seg6.c

···
 	.parallel_ops	= true,
 	.ops		= seg6_genl_ops,
 	.n_ops		= ARRAY_SIZE(seg6_genl_ops),
+	.resv_start_op	= SEG6_CMD_GET_TUNSRC + 1,
 	.module		= THIS_MODULE,
 };
 

net/l2tp/l2tp_netlink.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= l2tp_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(l2tp_nl_ops),
+	.resv_start_op	= L2TP_CMD_SESSION_GET + 1,
 	.mcgrps		= l2tp_multicast_group,
 	.n_mcgrps	= ARRAY_SIZE(l2tp_multicast_group),
 };

net/mptcp/pm_netlink.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= mptcp_pm_ops,
 	.n_small_ops	= ARRAY_SIZE(mptcp_pm_ops),
+	.resv_start_op	= MPTCP_PM_CMD_SUBFLOW_DESTROY + 1,
 	.mcgrps		= mptcp_pm_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(mptcp_pm_mcgrps),
 };

net/ncsi/ncsi-netlink.c

···
 	.module = THIS_MODULE,
 	.small_ops = ncsi_ops,
 	.n_small_ops = ARRAY_SIZE(ncsi_ops),
+	.resv_start_op = NCSI_CMD_SET_CHANNEL_MASK + 1,
 };
 
 static int __init ncsi_init_netlink(void)

net/netfilter/ipvs/ip_vs_ctl.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= ip_vs_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(ip_vs_genl_ops),
+	.resv_start_op	= IPVS_CMD_FLUSH + 1,
 };
 
 static int __init ip_vs_genl_register(void)

net/netlabel/netlabel_calipso.c

···
 	.module = THIS_MODULE,
 	.small_ops = netlbl_calipso_ops,
 	.n_small_ops = ARRAY_SIZE(netlbl_calipso_ops),
+	.resv_start_op = NLBL_CALIPSO_C_LISTALL + 1,
 };
 
 /* NetLabel Generic NETLINK Protocol Functions

net/netlabel/netlabel_cipso_v4.c

···
 	.module = THIS_MODULE,
 	.small_ops = netlbl_cipsov4_ops,
 	.n_small_ops = ARRAY_SIZE(netlbl_cipsov4_ops),
+	.resv_start_op = NLBL_CIPSOV4_C_LISTALL + 1,
 };
 
 /*

net/netlabel/netlabel_mgmt.c

···
 	.module = THIS_MODULE,
 	.small_ops = netlbl_mgmt_genl_ops,
 	.n_small_ops = ARRAY_SIZE(netlbl_mgmt_genl_ops),
+	.resv_start_op = NLBL_MGMT_C_VERSION + 1,
 };
 
 /*

net/netlabel/netlabel_unlabeled.c

···
 	.module = THIS_MODULE,
 	.small_ops = netlbl_unlabel_genl_ops,
 	.n_small_ops = ARRAY_SIZE(netlbl_unlabel_genl_ops),
+	.resv_start_op = NLBL_UNLABEL_C_STATICLISTDEF + 1,
 };
 
 /*

net/netlink/genetlink.c

···
 	if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))
 		return -EINVAL;
 
+	if (hdr->cmd >= family->resv_start_op && hdr->reserved)
+		return -EINVAL;
+
 	if (genl_get_cmd(hdr->cmd, family, &op))
 		return -EOPNOTSUPP;
 
···
 	.module = THIS_MODULE,
 	.ops = genl_ctrl_ops,
 	.n_ops = ARRAY_SIZE(genl_ctrl_ops),
+	.resv_start_op = CTRL_CMD_GETPOLICY + 1,
 	.mcgrps = genl_ctrl_groups,
 	.n_mcgrps = ARRAY_SIZE(genl_ctrl_groups),
 	.id = GENL_ID_CTRL,

net/nfc/netlink.c

···
 	.module = THIS_MODULE,
 	.ops = nfc_genl_ops,
 	.n_ops = ARRAY_SIZE(nfc_genl_ops),
+	.resv_start_op = NFC_CMD_DEACTIVATE_TARGET + 1,
 	.mcgrps = nfc_genl_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(nfc_genl_mcgrps),
 };

net/openvswitch/conntrack.c

···
 	.parallel_ops = true,
 	.small_ops = ct_limit_genl_ops,
 	.n_small_ops = ARRAY_SIZE(ct_limit_genl_ops),
+	.resv_start_op = OVS_CT_LIMIT_CMD_GET + 1,
 	.mcgrps = &ovs_ct_limit_multicast_group,
 	.n_mcgrps = 1,
 	.module = THIS_MODULE,

net/openvswitch/datapath.c

···
 	.parallel_ops = true,
 	.small_ops = dp_packet_genl_ops,
 	.n_small_ops = ARRAY_SIZE(dp_packet_genl_ops),
+	.resv_start_op = OVS_PACKET_CMD_EXECUTE + 1,
 	.module = THIS_MODULE,
 };
 
···
 	.parallel_ops = true,
 	.small_ops = dp_flow_genl_ops,
 	.n_small_ops = ARRAY_SIZE(dp_flow_genl_ops),
+	.resv_start_op = OVS_FLOW_CMD_SET + 1,
 	.mcgrps = &ovs_dp_flow_multicast_group,
 	.n_mcgrps = 1,
 	.module = THIS_MODULE,
···
 	.parallel_ops = true,
 	.small_ops = dp_datapath_genl_ops,
 	.n_small_ops = ARRAY_SIZE(dp_datapath_genl_ops),
+	.resv_start_op = OVS_DP_CMD_SET + 1,
 	.mcgrps = &ovs_dp_datapath_multicast_group,
 	.n_mcgrps = 1,
 	.module = THIS_MODULE,

net/openvswitch/meter.c

···
 	.parallel_ops = true,
 	.small_ops = dp_meter_genl_ops,
 	.n_small_ops = ARRAY_SIZE(dp_meter_genl_ops),
+	.resv_start_op = OVS_METER_CMD_GET + 1,
 	.mcgrps = &ovs_meter_multicast_group,
 	.n_mcgrps = 1,
 	.module = THIS_MODULE,

net/psample/psample.c

···
 	.mcgrps		= psample_nl_mcgrps,
 	.small_ops	= psample_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(psample_nl_ops),
+	.resv_start_op	= PSAMPLE_CMD_GET_GROUP + 1,
 	.n_mcgrps	= ARRAY_SIZE(psample_nl_mcgrps),
 };
 

net/smc/smc_netlink.c

···
 	.netnsok =	true,
 	.module =	THIS_MODULE,
 	.ops =		smc_gen_nl_ops,
-	.n_ops =	ARRAY_SIZE(smc_gen_nl_ops)
+	.n_ops =	ARRAY_SIZE(smc_gen_nl_ops),
+	.resv_start_op = SMC_NETLINK_DISABLE_HS_LIMITATION + 1,
 };
 
 int __init smc_nl_init(void)

net/smc/smc_pnet.c

···
 	.netnsok = true,
 	.module = THIS_MODULE,
 	.ops = smc_pnet_ops,
-	.n_ops =  ARRAY_SIZE(smc_pnet_ops)
+	.n_ops =  ARRAY_SIZE(smc_pnet_ops),
+	.resv_start_op = SMC_PNETID_FLUSH + 1,
 };
 
 bool smc_pnet_is_ndev_pnetid(struct net *net, u8 *pnetid)

net/tipc/netlink.c

···
 	.module		= THIS_MODULE,
 	.ops		= tipc_genl_v2_ops,
 	.n_ops		= ARRAY_SIZE(tipc_genl_v2_ops),
+	.resv_start_op	= TIPC_NL_ADDR_LEGACY_GET + 1,
 };
 
 int __init tipc_netlink_start(void)

net/tipc/netlink_compat.c

···
 	.module		= THIS_MODULE,
 	.small_ops	= tipc_genl_compat_ops,
 	.n_small_ops	= ARRAY_SIZE(tipc_genl_compat_ops),
+	.resv_start_op	= TIPC_GENL_CMD + 1,
 };
 
 int __init tipc_netlink_compat_start(void)

net/wireless/nl80211.c

···
 	.n_ops = ARRAY_SIZE(nl80211_ops),
 	.small_ops = nl80211_small_ops,
 	.n_small_ops = ARRAY_SIZE(nl80211_small_ops),
+	.resv_start_op = NL80211_CMD_REMOVE_LINK_STA + 1,
 	.mcgrps = nl80211_mcgrps,
 	.n_mcgrps = ARRAY_SIZE(nl80211_mcgrps),
 	.parallel_ops = true,