tipc: fix unitilized skb list crash

Our test suite somtimes provokes the following crash:

Description of problem:
[ 1092.597234] BUG: unable to handle kernel NULL pointer dereference at 00000000000000e8
[ 1092.605072] PGD 0 P4D 0
[ 1092.607620] Oops: 0000 [#1] SMP PTI
[ 1092.611118] CPU: 37 PID: 0 Comm: swapper/37 Kdump: loaded Not tainted 4.18.0-122.el8.x86_64 #1
[ 1092.619724] Hardware name: Dell Inc. PowerEdge R740/08D89F, BIOS 1.3.7 02/08/2018
[ 1092.627215] RIP: 0010:tipc_mcast_filter_msg+0x93/0x2d0 [tipc]
[ 1092.632955] Code: 0f 84 aa 01 00 00 89 cf 4d 01 ca 4c 8b 26 c1 ef 19 83 e7 0f 83 ff 0c 4d 0f 45 d1 41 8b 6a 10 0f cd 4c 39 e6 0f 84 81 01 00 00 <4d> 8b 9c 24 e8 00 00 00 45 8b 13 41 0f ca 44 89 d7 c1 ef 13 83 e7
[ 1092.651703] RSP: 0018:ffff929e5fa83a18 EFLAGS: 00010282
[ 1092.656927] RAX: ffff929e3fb38100 RBX: 00000000069f29ee RCX: 00000000416c0045
[ 1092.664058] RDX: ffff929e5fa83a88 RSI: ffff929e31a28420 RDI: 0000000000000000
[ 1092.671209] RBP: 0000000029b11821 R08: 0000000000000000 R09: ffff929e39b4407a
[ 1092.678343] R10: ffff929e39b4407a R11: 0000000000000007 R12: 0000000000000000
[ 1092.685475] R13: 0000000000000001 R14: ffff929e3fb38100 R15: ffff929e39b4407a
[ 1092.692614] FS:  0000000000000000(0000) GS:ffff929e5fa80000(0000) knlGS:0000000000000000
[ 1092.700702] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1092.706447] CR2: 00000000000000e8 CR3: 000000031300a004 CR4: 00000000007606e0
[ 1092.713579] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1092.720712] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1092.727843] PKRU: 55555554
[ 1092.730556] Call Trace:
[ 1092.733010]  <IRQ>
[ 1092.735034]  tipc_sk_filter_rcv+0x7ca/0xb80 [tipc]
[ 1092.739828]  ? __kmalloc_node_track_caller+0x1cb/0x290
[ 1092.744974]  ? dev_hard_start_xmit+0xa5/0x210
[ 1092.749332]  tipc_sk_rcv+0x389/0x640 [tipc]
[ 1092.753519]  tipc_sk_mcast_rcv+0x23c/0x3a0 [tipc]
[ 1092.758224]  tipc_rcv+0x57a/0xf20 [tipc]
[ 1092.762154]  ? ktime_get_real_ts64+0x40/0xe0
[ 1092.766432]  ? tpacket_rcv+0x50/0x9f0
[ 1092.770098]  tipc_l2_rcv_msg+0x4a/0x70 [tipc]
[ 1092.774452]  __netif_receive_skb_core+0xb62/0xbd0
[ 1092.779164]  ? enqueue_entity+0xf6/0x630
[ 1092.783084]  ? kmem_cache_alloc+0x158/0x1c0
[ 1092.787272]  ? __build_skb+0x25/0xd0
[ 1092.790849]  netif_receive_skb_internal+0x42/0xf0
[ 1092.795557]  napi_gro_receive+0xba/0xe0
[ 1092.799417]  mlx5e_handle_rx_cqe+0x83/0xd0 [mlx5_core]
[ 1092.804564]  mlx5e_poll_rx_cq+0xd5/0x920 [mlx5_core]
[ 1092.809536]  mlx5e_napi_poll+0xb2/0xce0 [mlx5_core]
[ 1092.814415]  ? __wake_up_common_lock+0x89/0xc0
[ 1092.818861]  net_rx_action+0x149/0x3b0
[ 1092.822616]  __do_softirq+0xe3/0x30a
[ 1092.826193]  irq_exit+0x100/0x110
[ 1092.829512]  do_IRQ+0x85/0xd0
[ 1092.832483]  common_interrupt+0xf/0xf
[ 1092.836147]  </IRQ>
[ 1092.838255] RIP: 0010:cpuidle_enter_state+0xb7/0x2a0
[ 1092.843221] Code: e8 3e 79 a5 ff 80 7c 24 03 00 74 17 9c 58 0f 1f 44 00 00 f6 c4 02 0f 85 d7 01 00 00 31 ff e8 a0 6b ab ff fb 66 0f 1f 44 00 00 <48> b8 ff ff ff ff f3 01 00 00 4c 29 f3 ba ff ff ff 7f 48 39 c3 7f
[ 1092.861967] RSP: 0018:ffffaa5ec6533e98 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffdd
[ 1092.869530] RAX: ffff929e5faa3100 RBX: 000000fe63dd2092 RCX: 000000000000001f
[ 1092.876665] RDX: 000000fe63dd2092 RSI: 000000003a518aaa RDI: 0000000000000000
[ 1092.883795] RBP: 0000000000000003 R08: 0000000000000004 R09: 0000000000022940
[ 1092.890929] R10: 0000040cb0666b56 R11: ffff929e5faa20a8 R12: ffff929e5faade78
[ 1092.898060] R13: ffffffffb59258f8 R14: 000000fe60f3228d R15: 0000000000000000
[ 1092.905196]  ? cpuidle_enter_state+0x92/0x2a0
[ 1092.909555]  do_idle+0x236/0x280
[ 1092.912785]  cpu_startup_entry+0x6f/0x80
[ 1092.916715]  start_secondary+0x1a7/0x200
[ 1092.920642]  secondary_startup_64+0xb7/0xc0
[...]

The reason is that the skb list tipc_socket::mc_method.deferredq only
is initialized for connectionless sockets, while nothing stops arriving
multicast messages from being filtered by connection oriented sockets,
with subsequent access to the said list.

We fix this by initializing the list unconditionally at socket creation.
This eliminates the crash, while the message still is dropped further
down in tipc_sk_filter_rcv() as it should be.
Reported-by: Li Shuang <shuali@redhat.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -485,9 +485,8 @@ static int tipc_sk_create(struct net *net, struct socket *sock,
 		tsk_set_unreturnable(tsk, true);
 		if (sock->type == SOCK_DGRAM)
 			tsk_set_unreliable(tsk, true);
-		__skb_queue_head_init(&tsk->mc_method.deferredq);
 	}
-
+	__skb_queue_head_init(&tsk->mc_method.deferredq);
 	trace_tipc_sk_create(sk, NULL, TIPC_DUMP_NONE, " ");
 	return 0;
 }