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: 925d046e7e52 ("RDMA/core: Add a netevent notifier to cma") 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 --- drivers/infiniband/core/cma.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c index 91db10515d74..176d0b3e4488 100644 --- a/drivers/infiniband/core/cma.c +++ b/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); }