IB/core: Avoid crash on pkey enforcement failed in received MADs

Below kernel crash is observed when Pkey security enforcement fails on
received MADs. This issue is reported in [1].

ib_free_recv_mad() accesses the rmpp_list, whose initialization is
needed before accessing it.
When security enformcent fails on received MADs, MAD processing avoided
due to security checks failed.

OpenSM[3770]: SM port is down
kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
kernel: IP: ib_free_recv_mad+0x44/0xa0 [ib_core]
kernel: PGD 0
kernel: P4D 0
kernel:
kernel: Oops: 0002 [#1] SMP
kernel: CPU: 0 PID: 2833 Comm: kworker/0:1H Tainted: P          IO    4.13.4-1-pve #1
kernel: Hardware name: Dell       XS23-TY3        /9CMP63, BIOS 1.71 09/17/2013
kernel: Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
kernel: task: ffffa069c6541600 task.stack: ffffb9a729054000
kernel: RIP: 0010:ib_free_recv_mad+0x44/0xa0 [ib_core]
kernel: RSP: 0018:ffffb9a729057d38 EFLAGS: 00010286
kernel: RAX: ffffa069cb138a48 RBX: ffffa069cb138a10 RCX: 0000000000000000
kernel: RDX: ffffb9a729057d38 RSI: 0000000000000000 RDI: ffffa069cb138a20
kernel: RBP: ffffb9a729057d60 R08: ffffa072d2d49800 R09: ffffa069cb138ae0
kernel: R10: ffffa069cb138ae0 R11: ffffa072b3994e00 R12: ffffb9a729057d38
kernel: R13: ffffa069d1c90000 R14: 0000000000000000 R15: ffffa069d1c90880
kernel: FS:  0000000000000000(0000) GS:ffffa069dba00000(0000) knlGS:0000000000000000
kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kernel: CR2: 0000000000000008 CR3: 00000011f51f2000 CR4: 00000000000006f0
kernel: Call Trace:
kernel:  ib_mad_recv_done+0x5cc/0xb50 [ib_core]
kernel:  __ib_process_cq+0x5c/0xb0 [ib_core]
kernel:  ib_cq_poll_work+0x20/0x60 [ib_core]
kernel:  process_one_work+0x1e9/0x410
kernel:  worker_thread+0x4b/0x410
kernel:  kthread+0x109/0x140
kernel:  ? process_one_work+0x410/0x410
kernel:  ? kthread_create_on_node+0x70/0x70
kernel:  ? SyS_exit_group+0x14/0x20
kernel:  ret_from_fork+0x25/0x30
kernel: RIP: ib_free_recv_mad+0x44/0xa0 [ib_core] RSP: ffffb9a729057d38
kernel: CR2: 0000000000000008

[1] : https://www.spinics.net/lists/linux-rdma/msg56190.html

Fixes: 47a2b338 ("IB/core: Enforce security on management datagrams")
Cc: stable@vger.kernel.org # 4.13+
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reported-by: Chris Blake <chrisrblake93@gmail.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Reviewed-by: Hal Rosenstock <hal@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/mad.c

@@ -1974,14 +1974,15 @@ static void ib_mad_complete_recv(struct ib_mad_agent_private *mad_agent_priv,
 	unsigned long flags;
 	int ret;
 
+	INIT_LIST_HEAD(&mad_recv_wc->rmpp_list);
 	ret = ib_mad_enforce_security(mad_agent_priv,
 				      mad_recv_wc->wc->pkey_index);
 	if (ret) {
 		ib_free_recv_mad(mad_recv_wc);
 		deref_mad_agent(mad_agent_priv);
+		return;
 	}
 
-	INIT_LIST_HEAD(&mad_recv_wc->rmpp_list);
 	list_add(&mad_recv_wc->recv_buf.list, &mad_recv_wc->rmpp_list);
 	if (ib_mad_kernel_rmpp_agent(&mad_agent_priv->agent)) {
 		mad_recv_wc = ib_process_rmpp_recv_wc(mad_agent_priv,