RDMA/cma: Fix workqueue crash in cma_netevent_work_handler

struct rdma_cm_id has member "struct work_struct net_work"
that is reused for enqueuing cma_netevent_work_handler()s
onto cma_wq.

Below crash[1] can occur if more than one call to
cma_netevent_callback() occurs in quick succession,
which further enqueues cma_netevent_work_handler()s for the
same rdma_cm_id, overwriting any previously queued work-item(s)
that was just scheduled to run i.e. there is no guarantee
the queued work item may run between two successive calls
to cma_netevent_callback() and the 2nd INIT_WORK would overwrite
the 1st work item (for the same rdma_cm_id), despite grabbing
id_table_lock during enqueue.

Also drgn analysis [2] indicates the work item was likely overwritten.

Fix this by moving the INIT_WORK() to __rdma_create_id(),
so that it doesn't race with any existing queue_work() or
its worker thread.

[1] Trimmed crash stack:
=============================================
BUG: kernel NULL pointer dereference, address: 0000000000000008
kworker/u256:6 ... 6.12.0-0...
Workqueue:  cma_netevent_work_handler [rdma_cm] (rdma_cm)
RIP: 0010:process_one_work+0xba/0x31a
Call Trace:
 worker_thread+0x266/0x3a0
 kthread+0xcf/0x100
 ret_from_fork+0x31/0x50
 ret_from_fork_asm+0x1a/0x30
=============================================

[2] drgn crash analysis:

>>> trace = prog.crashed_thread().stack_trace()
>>> trace
(0)  crash_setup_regs (./arch/x86/include/asm/kexec.h:111:15)
(1)  __crash_kexec (kernel/crash_core.c:122:4)
(2)  panic (kernel/panic.c:399:3)
(3)  oops_end (arch/x86/kernel/dumpstack.c:382:3)
...
(8)  process_one_work (kernel/workqueue.c:3168:2)
(9)  process_scheduled_works (kernel/workqueue.c:3310:3)
(10) worker_thread (kernel/workqueue.c:3391:4)
(11) kthread (kernel/kthread.c:389:9)

Line workqueue.c:3168 for this kernel version is in process_one_work():
3168	strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);

>>> trace[8]["work"]
*(struct work_struct *)0xffff92577d0a21d8 = {
	.data = (atomic_long_t){
		.counter = (s64)536870912,    <=== Note
	},
	.entry = (struct list_head){
		.next = (struct list_head *)0xffff924d075924c0,
		.prev = (struct list_head *)0xffff924d075924c0,
	},
	.func = (work_func_t)cma_netevent_work_handler+0x0 = 0xffffffffc2cec280,
}

Suspicion is that pwq is NULL:
>>> trace[8]["pwq"]
(struct pool_workqueue *)<absent>

In process_one_work(), pwq is assigned from:
struct pool_workqueue *pwq = get_work_pwq(work);

and get_work_pwq() is:
static struct pool_workqueue *get_work_pwq(struct work_struct *work)
{
 	unsigned long data = atomic_long_read(&work->data);

 	if (data & WORK_STRUCT_PWQ)
 		return work_struct_pwq(data);
 	else
 		return NULL;
}

WORK_STRUCT_PWQ is 0x4:
>>> print(repr(prog['WORK_STRUCT_PWQ']))
Object(prog, 'enum work_flags', value=4)

But work->data is 536870912 which is 0x20000000.
So, get_work_pwq() returns NULL and we crash in process_one_work():
3168	strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);
=============================================

Fixes: 925d046 ("RDMA/core: Add a netevent notifier to cma")
Cc: stable@vger.kernel.org
Co-developed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Sharath Srinivasan <sharath.srinivasan@oracle.com>
Reviewed-by: Patrisious Haddad <phaddad@nvidia.com>
Link: https://patch.msgid.link/bf0082f9-5b25-4593-92c6-d130aa8ba439@oracle.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/core/cma.c

@@ -72,6 +72,8 @@ static const char * const cma_events[] = {
 static void cma_iboe_set_mgid(struct sockaddr *addr, union ib_gid *mgid,
 			      enum ib_gid_type gid_type);
 
+static void cma_netevent_work_handler(struct work_struct *_work);
+
 const char *__attribute_const__ rdma_event_msg(enum rdma_cm_event_type event)
 {
 	size_t index = event;
@@ -1047,6 +1049,7 @@ __rdma_create_id(struct net *net, rdma_cm_event_handler event_handler,
 	get_random_bytes(&id_priv->seq_num, sizeof id_priv->seq_num);
 	id_priv->id.route.addr.dev_addr.net = get_net(net);
 	id_priv->seq_num &= 0x00ffffff;
+	INIT_WORK(&id_priv->id.net_work, cma_netevent_work_handler);
 
 	rdma_restrack_new(&id_priv->res, RDMA_RESTRACK_CM_ID);
 	if (parent)
@@ -5241,7 +5244,6 @@ static int cma_netevent_callback(struct notifier_block *self,
 		if (!memcmp(current_id->id.route.addr.dev_addr.dst_dev_addr,
 			   neigh->ha, ETH_ALEN))
 			continue;
-		INIT_WORK(&current_id->id.net_work, cma_netevent_work_handler);
 		cma_id_get(current_id);
 		queue_work(cma_wq, &current_id->id.net_work);
 	}