RDMA/cma: Fix workqueue crash in cma_netevent_work_handler

JIRA: https://issues.redhat.com/browse/RHEL-75591

commit 45f5dcd
Author: Sharath Srinivasan <[email protected]>
Date:   Wed Mar 26 14:05:32 2025 -0700

    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: [email protected]
    Co-developed-by: Håkon Bugge <[email protected]>
    Signed-off-by: Håkon Bugge <[email protected]>
    Signed-off-by: Sharath Srinivasan <[email protected]>
    Reviewed-by: Patrisious Haddad <[email protected]>
    Link: https://patch.msgid.link/[email protected]
    Signed-off-by: Leon Romanovsky <[email protected]>

Signed-off-by: Kamal Heib <[email protected]>

Author: Kamalheib

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;
@@ -1033,6 +1035,7 @@ __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)
@@ -5227,7 +5230,6 @@ 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);
 	}