selinux: prevent KMSAN warning in selinux_inet_conn_request()

KMSAN reports the following issue:
[   81.822503] =====================================================
[   81.823222] BUG: KMSAN: uninit-value in selinux_inet_conn_request+0x2c8/0x4b0
[   81.823891]  selinux_inet_conn_request+0x2c8/0x4b0
[   81.824385]  security_inet_conn_request+0xc0/0x160
[   81.824886]  tcp_v4_route_req+0x30e/0x490
[   81.825343]  tcp_conn_request+0xdc8/0x3400
[   81.825813]  tcp_v4_conn_request+0x134/0x190
[   81.826292]  tcp_rcv_state_process+0x1f4/0x3b40
[   81.826797]  tcp_v4_do_rcv+0x9ca/0xc30
[   81.827236]  tcp_v4_rcv+0x3bf5/0x4180
[   81.827670]  ip_protocol_deliver_rcu+0x822/0x1230
[   81.828174]  ip_local_deliver_finish+0x259/0x370
[   81.828667]  ip_local_deliver+0x1c0/0x450
[   81.829105]  ip_sublist_rcv+0xdc1/0xf50
[   81.829534]  ip_list_rcv+0x72e/0x790
[   81.829941]  __netif_receive_skb_list_core+0x10d5/0x1180
[   81.830499]  netif_receive_skb_list_internal+0xc41/0x1190
[   81.831064]  napi_complete_done+0x2c4/0x8b0
[   81.831532]  e1000_clean+0x12bf/0x4d90
[   81.831983]  __napi_poll+0xa6/0x760
[   81.832391]  net_rx_action+0x84c/0x1550
[   81.832831]  __do_softirq+0x272/0xa6c
[   81.833239]  __irq_exit_rcu+0xb7/0x1a0
[   81.833654]  irq_exit_rcu+0x17/0x40
[   81.834044]  common_interrupt+0x8d/0xa0
[   81.834494]  asm_common_interrupt+0x2b/0x40
[   81.834949]  default_idle+0x17/0x20
[   81.835356]  arch_cpu_idle+0xd/0x20
[   81.835766]  default_idle_call+0x43/0x70
[   81.836210]  do_idle+0x258/0x800
[   81.836581]  cpu_startup_entry+0x26/0x30
[   81.837002]  __pfx_ap_starting+0x0/0x10
[   81.837444]  secondary_startup_64_no_verify+0x17a/0x17b
[   81.837979]
[   81.838166] Local variable nlbl_type.i created at:
[   81.838596]  selinux_inet_conn_request+0xe3/0x4b0
[   81.839078]  security_inet_conn_request+0xc0/0x160

KMSAN warning is reproducible with:
* netlabel_mgmt_protocount is 0 (e.g. netlbl_enabled() returns 0)
* CONFIG_SECURITY_NETWORK_XFRM may be set or not
* CONFIG_KMSAN=y
* `ssh USER@HOSTNAME /bin/date`

selinux_skb_peerlbl_sid() will call selinux_xfrm_skb_sid(), then fall
to selinux_netlbl_skbuff_getsid() which will not initialize nlbl_type,
but it will be passed to:

    err = security_net_peersid_resolve(nlbl_sid,
                                       nlbl_type, xfrm_sid, sid);

and checked by KMSAN, although it will not be used inside
security_net_peersid_resolve() (at least now), since this function
will check either (xfrm_sid == SECSID_NULL) or (nlbl_sid ==
SECSID_NULL) first and return before using uninitialized nlbl_type.

Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
[PM: subject line tweak, removed 'fixes' tag as code is not broken]
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/netlabel.c

@@ -198,6 +198,7 @@ int selinux_netlbl_skbuff_getsid(struct sk_buff *skb,
 	struct netlbl_lsm_secattr secattr;
 
 	if (!netlbl_enabled()) {
+		*type = NETLBL_NLTYPE_NONE;
 		*sid = SECSID_NULL;
 		return 0;
 	}